http://soft-matter.seas.harvard.edu/api.php?action=feedcontributions&user=Kmiller&feedformat=atomSoft-Matter - User contributions [en]2020-12-04T17:54:29ZUser contributionsMediaWiki 1.24.2http://soft-matter.seas.harvard.edu/index.php?title=Contact_Angle_Hysteresis_and_Interacting_Surface_Defects&diff=24344Contact Angle Hysteresis and Interacting Surface Defects2012-04-26T02:00:05Z<p>Kmiller: </p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Contact Angle Hysteresis and Interacting Surface Defects<br />
<br />
Author: J.M. di Meglio<br />
<br />
Journal: "Europhysics Letters" 17 (7), (1992); 607-612<br />
<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is contact angle hysteresis, a process that sometimes occurs for non-wetting liquids. Contact angle hysteresis is when a liquid drop is moved on a solid and the contact angle ahead of the drop is larger than the contact angle at the rear and it is not a dynamical effect, i.e. it only occurs at very small velocities. Contact angle hysteresis is commonly attributed to surface defects in the solid (chemical heterogeneities or roughness). The paper focusses on the pinning of an advancing triple line on nondiluted defects (that have a long range of capillary interactions). The contact line has a long-range tail on each side of the defect and when the solid plane is vertical, the tail length is controlled by the capillary length. The capillary length is the length scale for a fluid that is under the competing forces of gravity and surface tension. This paper describes experiments to show the connection between defects and contact angle hysteresis. <br />
<br />
<br />
== Experiments ==<br />
<br />
The experiments involved overhead projector transparencies with defects represented as circular spots drawn using a plotter. Two sets of samples were made: one set with 1.5mm circular spots (type 1) patched randomly and with variable concentrations (Fig 2a below), the other with 0.5mm defects more uniformly distributed over the transparency (type 2) (Fig 2b below). The strength of the defects are changed by using different types of ink. <br />
<br />
The large defect samples were wetted with hexadecane and the small-defect samples were wetted with heptane.<br />
The defects had a size comparable to the capillary length and both liquids exhibited contact angle hysteresis on the defects. <br />
<br />
[[Image:Fig 1 wiki.png]]<br />
<br />
The samples were hung up to a force sensor which was connected to an amplifier and this was used to measure both the advancing and receding force exerted by the liquid. The liquids were displaced across the sample with velocities between 40 and 600 microns/second. The sample was dipped into the liquid at constant velocity to measure the advancing liquid force. The sample was then removed out of the liquid (at the same velocity) and the receding force was measured. The hysteresis was calculated as the difference between these two forces.<br />
<br />
== Results ==<br />
<br />
Figure 3 depicts the relative hysteresis (hysteresis on a patched area divided by the hysteresis on the defect-free area) along the sample as a function of the density of defects for type 1 samples. When the concentration of defects is really low (as in the lowest case with only four bumps), each bump corresponds to a peak on the hysteresis axis. When the concentration of defects is increased, there are 'avalanches' in the contact line - corresponding to pinning-depinning of the contact line on islands of defects. As the concentration of defects increases, so too do the 'large-scale events' on the hysteresis axis. <br />
<br />
<br />
[[Image:Screen shot 2012-04-25 at 7.24.19 PM.png]]<br />
<br />
<br />
Figure 4 shows a plot of the increase in the mean hysteresis versus the density of defects (plotted on a log-log scale). On this plot, d* represents the critical density at which defects appear to interact with one another (i.e. above this density, the hysteresis is no longer increasing linearly). This critical density is around the square of the capillary length. The adjacent figure shows the root mean square amplitude of the noise (which increases with hysteresis). To gain a better understanding of the noise, the experimenters took another set of measurements with the type 2 samples which had a longer length of patched areas. <br />
<br />
[[Image:Km wiki.png]]<br />
<br />
<br />
Six different velocities were measured and it was found that the hysteresis increases a little with velocity (shown in the figure below). Figure 6 shows the increase of the mean hysteresis (averaged over the six velocities) plotted against the density of defects. A nonlinear behavior is noticed here but - not the same nonlinear relationship as the one shown in the plot above. The author had no explanation for this difference. <br />
<br />
The square of the spatial Fourier transform of the noise of the force in the region where defects were present was computed and plotted for the averaged hysteresis. This confirmed that the amplitude of the noise is important above the critical density (d*) and the noise follows a <math>1/f^2</math> behavior in the defect zone where the amplitude is most emphasized. This suggests that the pinning that occurred in this fall into a class of experiments of "avalanches of sandpiles or stick-and-slip related to self-organized criticality". (pg 610)<br />
<br />
[[Image:wiki_fig4_km.png]]<br />
<br />
== Conclusion ==<br />
<br />
The author admits that the noise level without a sample was only 1 order of magnitude smaller than the hysteresis noise and therefore, it was hard to draw definitive conclusions from these experiments. The high level of noise prevalent in these experiments made it difficult to investigate the relationship between the velocity of the fluid and the hysteresis. Regardless of this fact, the experiments described in this paper provide a very interesting (and simple) way of changing the strength of the defects (concentration of pinning points) and to study the length (and velocity) scales over which contact angle hysteresis exists.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Screen_shot_2012-04-25_at_7.24.19_PM.png&diff=24343File:Screen shot 2012-04-25 at 7.24.19 PM.png2012-04-26T01:59:32Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Contact_Angle_Hysteresis_and_Interacting_Surface_Defects&diff=24342Contact Angle Hysteresis and Interacting Surface Defects2012-04-26T01:58:43Z<p>Kmiller: /* Experiments */</p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Contact Angle Hysteresis and Interacting Surface Defects<br />
<br />
Author: J.M. di Meglio<br />
<br />
Journal: "Europhysics Letters" 17 (7), (1992); 607-612<br />
<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is contact angle hysteresis, a process that sometimes occurs for non-wetting liquids. Contact angle hysteresis is when a liquid drop is moved on a solid and the contact angle ahead of the drop is larger than the contact angle at the rear and it is not a dynamical effect, i.e. it only occurs at very small velocities. Contact angle hysteresis is commonly attributed to surface defects in the solid (chemical heterogeneities or roughness). The paper focusses on the pinning of an advancing triple line on nondiluted defects (that have a long range of capillary interactions). The contact line has a long-range tail on each side of the defect and when the solid plane is vertical, the tail length is controlled by the capillary length. The capillary length is the length scale for a fluid that is under the competing forces of gravity and surface tension. This paper describes experiments to show the connection between defects and contact angle hysteresis. <br />
<br />
<br />
== Experiments ==<br />
<br />
The experiments involved overhead projector transparencies with defects represented as circular spots drawn using a plotter. Two sets of samples were made: one set with 1.5mm circular spots (type 1) patched randomly and with variable concentrations (Fig 2a below), the other with 0.5mm defects more uniformly distributed over the transparency (type 2) (Fig 2b below). The strength of the defects are changed by using different types of ink. <br />
<br />
The large defect samples were wetted with hexadecane and the small-defect samples were wetted with heptane.<br />
The defects had a size comparable to the capillary length and both liquids exhibited contact angle hysteresis on the defects. <br />
<br />
[[Image:Fig 1 wiki.png]]<br />
<br />
The samples were hung up to a force sensor which was connected to an amplifier and this was used to measure both the advancing and receding force exerted by the liquid. The liquids were displaced across the sample with velocities between 40 and 600 microns/second. The sample was dipped into the liquid at constant velocity to measure the advancing liquid force. The sample was then removed out of the liquid (at the same velocity) and the receding force was measured. The hysteresis was calculated as the difference between these two forces.<br />
<br />
== Results ==<br />
<br />
Figure 3 depicts the relative hysteresis (hysteresis on a patched area divided by the hysteresis on the defect-free area) along the sample as a function of the density of defects for type 1 samples. When the concentration of defects is really low (as in the lowest case with only four bumps), each bump corresponds to a peak on the hysteresis axis. When the concentration of defects is increased, there are 'avalanches' in the contact line - corresponding to pinning-depinning of the contact line on islands of defects. As the concentration of defects increases, so too do the 'large-scale events' on the hysteresis axis. <br />
<br />
<br />
[[Image:Km_wiki.png]]<br />
<br />
Figure 4 shows a plot of the increase in the mean hysteresis versus the density of defects (plotted on a log-log scale). On this plot, d* represents the critical density at which defects appear to interact with one another (i.e. above this density, the hysteresis is no longer increasing linearly). This critical density is around the square of the capillary length. The adjacent figure shows the root mean square amplitude of the noise (which increases with hysteresis). To gain a better understanding of the noise, the experimenters took another set of measurements with the type 2 samples which had a longer length of patched areas. <br />
<br />
[[Image:Km wiki.png]]<br />
<br />
<br />
Six different velocities were measured and it was found that the hysteresis increases a little with velocity (shown in the figure below). Figure 6 shows the increase of the mean hysteresis (averaged over the six velocities) plotted against the density of defects. A nonlinear behavior is noticed here but - not the same nonlinear relationship as the one shown in the plot above. The author had no explanation for this difference. <br />
<br />
The square of the spatial Fourier transform of the noise of the force in the region where defects were present was computed and plotted for the averaged hysteresis. This confirmed that the amplitude of the noise is important above the critical density (d*) and the noise follows a <math>1/f^2</math> behavior in the defect zone where the amplitude is most emphasized. This suggests that the pinning that occurred in this fall into a class of experiments of "avalanches of sandpiles or stick-and-slip related to self-organized criticality". (pg 610)<br />
<br />
[[Image:wiki_fig4_km.png]]<br />
<br />
== Conclusion ==<br />
<br />
The author admits that the noise level without a sample was only 1 order of magnitude smaller than the hysteresis noise and therefore, it was hard to draw definitive conclusions from these experiments. The high level of noise prevalent in these experiments made it difficult to investigate the relationship between the velocity of the fluid and the hysteresis. Regardless of this fact, the experiments described in this paper provide a very interesting (and simple) way of changing the strength of the defects (concentration of pinning points) and to study the length (and velocity) scales over which contact angle hysteresis exists.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Contact_Angle_Hysteresis_and_Interacting_Surface_Defects&diff=24341Contact Angle Hysteresis and Interacting Surface Defects2012-04-26T01:58:12Z<p>Kmiller: /* Results */</p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Contact Angle Hysteresis and Interacting Surface Defects<br />
<br />
Author: J.M. di Meglio<br />
<br />
Journal: "Europhysics Letters" 17 (7), (1992); 607-612<br />
<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is contact angle hysteresis, a process that sometimes occurs for non-wetting liquids. Contact angle hysteresis is when a liquid drop is moved on a solid and the contact angle ahead of the drop is larger than the contact angle at the rear and it is not a dynamical effect, i.e. it only occurs at very small velocities. Contact angle hysteresis is commonly attributed to surface defects in the solid (chemical heterogeneities or roughness). The paper focusses on the pinning of an advancing triple line on nondiluted defects (that have a long range of capillary interactions). The contact line has a long-range tail on each side of the defect and when the solid plane is vertical, the tail length is controlled by the capillary length. The capillary length is the length scale for a fluid that is under the competing forces of gravity and surface tension. This paper describes experiments to show the connection between defects and contact angle hysteresis. <br />
<br />
<br />
== Experiments ==<br />
<br />
The experiments involved overhead projector transparencies with defects represented as circular spots drawn using a plotter. Two sets of samples were made: one set with 1.5mm circular spots (type 1) patched randomly and with variable concentrations (Fig 2a below), the other with 0.5mm defects more uniformly distributed over the transparency (type 2) (Fig 2b below). The strength of the defects are changed by using different types of ink. <br />
<br />
The large defect samples were wetted with hexadecane and the small-defect samples were wetted with heptane.<br />
The defects had a size comparable to the capillary length and both liquids exhibited contact angle hysteresis on the defects. <br />
<br />
[[Image:Fig 1 wiki.png]]<br />
<br />
The samples were hung up to a force sensor which was connected to an amplifier and this was used to measure both the advancing and receding force exerted by the liquid. The liquids were displaced across the sample with velocities between 40 and 600 microns/second. The sample was dipped into the liquid at constant velocity to measure the advancing liquid force. The sample was then removed out of the liquid (at the same velocity) and the receding force was measured. The hysteresis was calculated as the difference between these two forces. <br />
<br />
<br />
== Results ==<br />
<br />
Figure 3 depicts the relative hysteresis (hysteresis on a patched area divided by the hysteresis on the defect-free area) along the sample as a function of the density of defects for type 1 samples. When the concentration of defects is really low (as in the lowest case with only four bumps), each bump corresponds to a peak on the hysteresis axis. When the concentration of defects is increased, there are 'avalanches' in the contact line - corresponding to pinning-depinning of the contact line on islands of defects. As the concentration of defects increases, so too do the 'large-scale events' on the hysteresis axis. <br />
<br />
<br />
[[Image:Km_wiki.png]]<br />
<br />
Figure 4 shows a plot of the increase in the mean hysteresis versus the density of defects (plotted on a log-log scale). On this plot, d* represents the critical density at which defects appear to interact with one another (i.e. above this density, the hysteresis is no longer increasing linearly). This critical density is around the square of the capillary length. The adjacent figure shows the root mean square amplitude of the noise (which increases with hysteresis). To gain a better understanding of the noise, the experimenters took another set of measurements with the type 2 samples which had a longer length of patched areas. <br />
<br />
[[Image:Km wiki.png]]<br />
<br />
<br />
Six different velocities were measured and it was found that the hysteresis increases a little with velocity (shown in the figure below). Figure 6 shows the increase of the mean hysteresis (averaged over the six velocities) plotted against the density of defects. A nonlinear behavior is noticed here but - not the same nonlinear relationship as the one shown in the plot above. The author had no explanation for this difference. <br />
<br />
The square of the spatial Fourier transform of the noise of the force in the region where defects were present was computed and plotted for the averaged hysteresis. This confirmed that the amplitude of the noise is important above the critical density (d*) and the noise follows a <math>1/f^2</math> behavior in the defect zone where the amplitude is most emphasized. This suggests that the pinning that occurred in this fall into a class of experiments of "avalanches of sandpiles or stick-and-slip related to self-organized criticality". (pg 610)<br />
<br />
[[Image:wiki_fig4_km.png]]<br />
<br />
== Conclusion ==<br />
<br />
The author admits that the noise level without a sample was only 1 order of magnitude smaller than the hysteresis noise and therefore, it was hard to draw definitive conclusions from these experiments. The high level of noise prevalent in these experiments made it difficult to investigate the relationship between the velocity of the fluid and the hysteresis. Regardless of this fact, the experiments described in this paper provide a very interesting (and simple) way of changing the strength of the defects (concentration of pinning points) and to study the length (and velocity) scales over which contact angle hysteresis exists.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Km_wiki.png&diff=24340File:Km wiki.png2012-04-26T01:57:40Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Contact_Angle_Hysteresis_and_Interacting_Surface_Defects&diff=24339Contact Angle Hysteresis and Interacting Surface Defects2012-04-26T01:56:52Z<p>Kmiller: </p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Contact Angle Hysteresis and Interacting Surface Defects<br />
<br />
Author: J.M. di Meglio<br />
<br />
Journal: "Europhysics Letters" 17 (7), (1992); 607-612<br />
<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is contact angle hysteresis, a process that sometimes occurs for non-wetting liquids. Contact angle hysteresis is when a liquid drop is moved on a solid and the contact angle ahead of the drop is larger than the contact angle at the rear and it is not a dynamical effect, i.e. it only occurs at very small velocities. Contact angle hysteresis is commonly attributed to surface defects in the solid (chemical heterogeneities or roughness). The paper focusses on the pinning of an advancing triple line on nondiluted defects (that have a long range of capillary interactions). The contact line has a long-range tail on each side of the defect and when the solid plane is vertical, the tail length is controlled by the capillary length. The capillary length is the length scale for a fluid that is under the competing forces of gravity and surface tension. This paper describes experiments to show the connection between defects and contact angle hysteresis. <br />
<br />
<br />
== Experiments ==<br />
<br />
The experiments involved overhead projector transparencies with defects represented as circular spots drawn using a plotter. Two sets of samples were made: one set with 1.5mm circular spots (type 1) patched randomly and with variable concentrations (Fig 2a below), the other with 0.5mm defects more uniformly distributed over the transparency (type 2) (Fig 2b below). The strength of the defects are changed by using different types of ink. <br />
<br />
The large defect samples were wetted with hexadecane and the small-defect samples were wetted with heptane.<br />
The defects had a size comparable to the capillary length and both liquids exhibited contact angle hysteresis on the defects. <br />
<br />
[[Image:Fig 1 wiki.png]]<br />
<br />
The samples were hung up to a force sensor which was connected to an amplifier and this was used to measure both the advancing and receding force exerted by the liquid. The liquids were displaced across the sample with velocities between 40 and 600 microns/second. The sample was dipped into the liquid at constant velocity to measure the advancing liquid force. The sample was then removed out of the liquid (at the same velocity) and the receding force was measured. The hysteresis was calculated as the difference between these two forces. <br />
<br />
<br />
== Results ==<br />
<br />
Figure 3 depicts the relative hysteresis (hysteresis on a patched area divided by the hysteresis on the defect-free area) along the sample as a function of the density of defects for type 1 samples. When the concentration of defects is really low (as in the lowest case with only four bumps), each bump corresponds to a peak on the hysteresis axis. When the concentration of defects is increased, there are 'avalanches' in the contact line - corresponding to pinning-depinning of the contact line on islands of defects. As the concentration of defects increases, so too do the 'large-scale events' on the hysteresis axis. <br />
<br />
<br />
[[Image:Km_wiki.png]]<br />
<br />
Figure 4 shows a plot of the increase in the mean hysteresis versus the density of defects (plotted on a log-log scale). On this plot, d* represents the critical density at which defects appear to interact with one another (i.e. above this density, the hysteresis is no longer increasing linearly). This critical density is around the square of the capillary length. The adjacent figure shows the root mean square amplitude of the noise (which increases with hysteresis). To gain a better understanding of the noise, the experimenters took another set of measurements with the type 2 samples which had a longer length of patched areas. <br />
<br />
[[Image:fig3_KM.png]]<br />
<br />
<br />
Six different velocities were measured and it was found that the hysteresis increases a little with velocity (shown in the figure below). Figure 6 shows the increase of the mean hysteresis (averaged over the six velocities) plotted against the density of defects. A nonlinear behavior is noticed here but - not the same nonlinear relationship as the one shown in the plot above. The author had no explanation for this difference. <br />
<br />
The square of the spatial Fourier transform of the noise of the force in the region where defects were present was computed and plotted for the averaged hysteresis. This confirmed that the amplitude of the noise is important above the critical density (d*) and the noise follows a <math>1/f^2</math> behavior in the defect zone where the amplitude is most emphasized. This suggests that the pinning that occurred in this fall into a class of experiments of "avalanches of sandpiles or stick-and-slip related to self-organized criticality". (pg 610)<br />
<br />
[[Image:wiki_fig4_km.png]]<br />
<br />
<br />
== Conclusion ==<br />
<br />
The author admits that the noise level without a sample was only 1 order of magnitude smaller than the hysteresis noise and therefore, it was hard to draw definitive conclusions from these experiments. The high level of noise prevalent in these experiments made it difficult to investigate the relationship between the velocity of the fluid and the hysteresis. Regardless of this fact, the experiments described in this paper provide a very interesting (and simple) way of changing the strength of the defects (concentration of pinning points) and to study the length (and velocity) scales over which contact angle hysteresis exists.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Contact_Angle_Hysteresis_and_Interacting_Surface_Defects&diff=24338Contact Angle Hysteresis and Interacting Surface Defects2012-04-26T01:56:08Z<p>Kmiller: New page: == Paper Details == Title: Contact Angle Hysteresis and Interacting Surface Defects Author: J.M. di Meglio Journal: "Europhysics Letters" 17 (7), (1992); 607-612 == Introduction ==...</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Contact Angle Hysteresis and Interacting Surface Defects<br />
<br />
Author: J.M. di Meglio<br />
<br />
Journal: "Europhysics Letters" 17 (7), (1992); 607-612<br />
<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is contact angle hysteresis, a process that sometimes occurs for non-wetting liquids. Contact angle hysteresis is when a liquid drop is moved on a solid and the contact angle ahead of the drop is larger than the contact angle at the rear and it is not a dynamical effect, i.e. it only occurs at very small velocities. Contact angle hysteresis is commonly attributed to surface defects in the solid (chemical heterogeneities or roughness). The paper focusses on the pinning of an advancing triple line on nondiluted defects (that have a long range of capillary interactions). The contact line has a long-range tail on each side of the defect and when the solid plane is vertical, the tail length is controlled by the capillary length. The capillary length is the length scale for a fluid that is under the competing forces of gravity and surface tension. This paper describes experiments to show the connection between defects and contact angle hysteresis. <br />
<br />
<br />
== Experiments ==<br />
<br />
The experiments involved overhead projector transparencies with defects represented as circular spots drawn using a plotter. Two sets of samples were made: one set with 1.5mm circular spots (type 1) patched randomly and with variable concentrations (Fig 2a below), the other with 0.5mm defects more uniformly distributed over the transparency (type 2) (Fig 2b below). The strength of the defects are changed by using different types of ink. <br />
<br />
The large defect samples were wetted with hexadecane and the small-defect samples were wetted with heptane.<br />
The defects had a size comparable to the capillary length and both liquids exhibited contact angle hysteresis on the defects. <br />
<br />
[[Image:Fig 1 wiki.png]]<br />
<br />
The samples were hung up to a force sensor which was connected to an amplifier and this was used to measure both the advancing and receding force exerted by the liquid. The liquids were displaced across the sample with velocities between 40 and 600 microns/second. The sample was dipped into the liquid at constant velocity to measure the advancing liquid force. The sample was then removed out of the liquid (at the same velocity) and the receding force was measured. The hysteresis was calculated as the difference between these two forces. <br />
<br />
<br />
== Results ==<br />
<br />
Figure 3 depicts the relative hysteresis (hysteresis on a patched area divided by the hysteresis on the defect-free area) along the sample as a function of the density of defects for type 1 samples. When the concentration of defects is really low (as in the lowest case with only four bumps), each bump corresponds to a peak on the hysteresis axis. When the concentration of defects is increased, there are 'avalanches' in the contact line - corresponding to pinning-depinning of the contact line on islands of defects. As the concentration of defects increases, so too do the 'large-scale events' on the hysteresis axis. <br />
<br />
<br />
[[Image:Km_wiki.png]]<br />
<br />
Figure 4 shows a plot of the increase in the mean hysteresis versus the density of defects (plotted on a log-log scale). On this plot, d* represents the critical density at which defects appear to interact with one another (i.e. above this density, the hysteresis is no longer increasing linearly). This critical density is around the square of the capillary length. The adjacent figure shows the root mean square amplitude of the noise (which increases with hysteresis). To gain a better understanding of the noise, the experimenters took another set of measurements with the type 2 samples which had a longer length of patched areas. <br />
<br />
[[Image:fig3_KM.png]]<br />
<br />
<br />
Six different velocities were measured and it was found that the hysteresis increases a little with velocity (shown in the figure below). Figure 6 shows the increase of the mean hysteresis (averaged over the six velocities) plotted against the density of defects. A nonlinear behavior is noticed here but - not the same nonlinear relationship as the one shown in the plot above. The author had no explanation for this difference. <br />
<br />
The square of the spatial Fourier transform of the noise of the force in the region where defects were present was computed and plotted for the averaged hysteresis. This confirmed that the amplitude of the noise is important above the critical density (d*) and the noise follows a <math>1/f^2</math> behavior in the defect zone where the amplitude is most emphasized. This suggests that the pinning that occurred in this fall into a class of experiments of "avalanches of sandpiles or stick-and-slip related to self-organized criticality". (pg 610)<br />
<br />
[[Image:wiki_fig4_km.png]]<br />
<br />
<br />
== Conclusion ==<br />
<br />
The author admits that the noise level without a sample was only 1 order of magnitude smaller than the hysteresis noise and therefore, it was hard to draw definitive conclusions from these experiments. The high level of noise prevalent in these experiments made it difficult to investigate the relationship between the velocity of the fluid and the hysteresis. Regardless of this fact, the experiments described in this paper provide a very interesting (and simple) way of changing the strength of the defects (concentration of pinning points) and to study the length (and velocity) scales over which contact angle hysteresis exists.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Wiki_fig4_km.png&diff=24337File:Wiki fig4 km.png2012-04-26T00:29:17Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Fig3_KM.png&diff=24336File:Fig3 KM.png2012-04-26T00:28:12Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Fig_1_wiki.png&diff=24335File:Fig 1 wiki.png2012-04-25T23:25:28Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Kelly_Miller&diff=24334Kelly Miller2012-04-25T23:21:20Z<p>Kmiller: </p>
<hr />
<div>Wiki entries for AP226 Capillarity and Wetting (Spring 2012)<br />
<br />
1. Deformable Interfaces<br />
<br />
[[Dynamic Forces Between Two Deformable Oil Droplets in Water]]<br />
<br />
[R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser, "Science"313 (2006): 210-213]<br />
<br />
<br />
2. Capillarity and Gravity<br />
<br />
[[Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer]]<br />
<br />
[C.B. Gorman, H.A. Biebuyck, G.M. Whitesides, "Langmuir" 11 (1995): 2242-2246]<br />
<br />
<br />
3. Long Range Forces<br />
<br />
[[Spreading of Nonvolatile Liquids in a Continuum Picture]]<br />
<br />
[ J.M. di Meglio, D. Quere, P.G. de Gennes, "Langmuir" 7 (1991); 335-338]<br />
<br />
<br />
4. Hysteresis and elasticity of the triple line<br />
<br />
[[Contact Angle Hysteresis and Interacting Surface Defects]]<br />
<br />
[J.M. di Meglio, "Europhysics Letters" 17 (7), (1992); 607-612]<br />
<br />
<br />
<br />
<br />
----<br />
----<br />
<br />
<br />
<br />
Wiki entries for AP225 Introduction to Soft Matter (Fall 2011)<br />
<br />
1. Introduction (Week 1):<br />
<br />
[[On The Movement of Small Particles Suspended in Stationary Liquids Required By The Molecular-Kinetic Theory of Heat]]<br />
<br />
[A. Einstein, ''Annalen der Physik'' 17 (1905): 549-560]<br />
<br />
<br />
2. Surface Forces and Disjoining Pressure (Week 2):<br />
<br />
[[Direct Measurement of Molecular Forces]]<br />
<br />
[B.V. Berjaguin, Y.I. Rabinovich, ''Nature'' 272 (1978): 313-318]<br />
<br />
<br />
3. Capillary and Wetting (Weeks 3 & 4)<br />
<br />
[[Thermodynamic deviations of the mechanical equilibrium conditions for fluid surfaces: Young's and Laplace's equations]]<br />
<br />
[P. Roura, "American Journal of Physics" 73 (12), (2005): 1139-1147<br />
<br />
<br />
4. Polymers (Weeks 5 &6)<br />
<br />
[[A Blind Spot in Confocal Reflection Microscopy: The Dependence of Fiber Brightness on Fiber Orientation in Imaging Biopolymer Networks]]<br />
<br />
[Jawerth, L.M., "Biophysical Journal" 98, (2009): L01-L03]<br />
<br />
<br />
5. Surfactants (Week 7)<br />
<br />
[[Krafft Points, Critical Micelle Concentrations, Surface Tension, and Solubilizing Power of Aqueous Solutions of Fluorinated Surfactants]]<br />
<br />
[Kunleda, Shinoda; The Journal of Physical Chemistry, Vol. 80, No. 22, 1976]<br />
<br />
<br />
6. Phases and phase diagrams (Week 8)<br />
<br />
[[Understanding Foods as Soft Materials]]<br />
<br />
[Mezzenga, R., Schurtenberger, A., Burbidge, A., Michel, M.; Nature Materials, Vol. 4, 2005]<br />
<br />
<br />
<br />
7. Charged Interfaces<br />
<br />
[[Hydrodynamics within the Electric Double Layer on Slipping Surfaces]]<br />
<br />
[Laurent J., Ybert, C., Trizac, E., Bocquet, L., Physical Review Letters, 93 (25), 2004]<br />
<br />
<br />
<br />
8. Thin "Soft" Films and Colloidal Stability<br />
<br />
[[A public study of the lifetime distribution of soap films]]<br />
<br />
[Tobin, S.T., Meagher, A.J., Bulfin, B., Mobius, M., Hutzler, S., American Journal of Physics, 79(8) 2011, pp. 819]</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24084Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:29:58Z<p>Kmiller: /* Conclusion */</p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: eqn_1.png]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn_2.png]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Spread3.png]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
In this case - both A and S are positive and the disjoining pressure (which is the slope of the P(e) versus e function) is monotonically decreasing). <br />
<br />
<br />
[[Image:eqn_4.png]]<br />
<br />
<br />
<br />
A small droplet in contact with a flat, solid surface spreads out and becomes a pancake (depicted below). How thick the film is is determined by the competition long-range forces, which tend to thicken the film, and S, which favors a large wet region. The equilibrium thickness corresponds to the minimum free energy.<br />
<br />
== Pseudo Partial Wetting ==<br />
<br />
When S>0 and A<0 we call this "pseudo" partial wetting<br />
<br />
In this case, the free energy must have a minimum at a certain value of film thickness. Depending on the volume of the drop, two regimes may arise:<br />
<br />
a) microscopic droplet with two possible modes of spreading: <br />
<br />
i) a "pancake" of finite thickness (see figure 3a)<br />
ii) a very dilute gas of molecules expanding indefinitely on the solid (thickness of film =0) (see figure 3b)<br />
<br />
<br />
[[Image:eqn_7.png]]<br />
<br />
<br />
<br />
[[Image:eqn_8.png]]<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
The situation in which S<0 and A>0 is referred to as partial wetting. In this case, the liquid droplet makes a non-zero finite contact angle (defined by the Young equation) on a dry surface. <br />
<br />
Young Equation<br />
<br />
<br />
[[Image:Eqn_9.png]]<br />
<br />
<br />
<br />
<br />
[[Image:Eqn_10.png]]<br />
<br />
== Conclusion ==<br />
<br />
<br />
This paper emphasized that the condition for complete wetting is not only when the spreading coefficient is positive, the sign of A has to be specified as well. The pseudo partial wetting regime is one in which the free energy has an absolute minimum at finite thickness.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24083Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:28:04Z<p>Kmiller: /* Partial Wetting */</p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: eqn_1.png]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn_2.png]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Spread3.png]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
In this case - both A and S are positive and the disjoining pressure (which is the slope of the P(e) versus e function) is monotonically decreasing). <br />
<br />
<br />
[[Image:eqn_4.png]]<br />
<br />
<br />
<br />
A small droplet in contact with a flat, solid surface spreads out and becomes a pancake (depicted below). How thick the film is is determined by the competition long-range forces, which tend to thicken the film, and S, which favors a large wet region. The equilibrium thickness corresponds to the minimum free energy.<br />
<br />
== Pseudo Partial Wetting ==<br />
<br />
When S>0 and A<0 we call this "pseudo" partial wetting<br />
<br />
In this case, the free energy must have a minimum at a certain value of film thickness. Depending on the volume of the drop, two regimes may arise:<br />
<br />
a) microscopic droplet with two possible modes of spreading: <br />
<br />
i) a "pancake" of finite thickness (see figure 3a)<br />
ii) a very dilute gas of molecules expanding indefinitely on the solid (thickness of film =0) (see figure 3b)<br />
<br />
<br />
[[Image:eqn_7.png]]<br />
<br />
<br />
<br />
[[Image:eqn_8.png]]<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
The situation in which S<0 and A>0 is referred to as partial wetting. In this case, the liquid droplet makes a non-zero finite contact angle (defined by the Young equation) on a dry surface. <br />
<br />
Young Equation<br />
<br />
<br />
[[Image:Eqn_9.png]]<br />
<br />
<br />
<br />
<br />
[[Image:Eqn_10.png]]<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_10.png&diff=24082File:Eqn 10.png2012-03-26T13:27:00Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_9.png&diff=24081File:Eqn 9.png2012-03-26T13:26:37Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24080Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:22:54Z<p>Kmiller: </p>
<hr />
<div>== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: eqn_1.png]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn_2.png]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Spread3.png]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
In this case - both A and S are positive and the disjoining pressure (which is the slope of the P(e) versus e function) is monotonically decreasing). <br />
<br />
<br />
[[Image:eqn_4.png]]<br />
<br />
<br />
<br />
A small droplet in contact with a flat, solid surface spreads out and becomes a pancake (depicted below). How thick the film is is determined by the competition long-range forces, which tend to thicken the film, and S, which favors a large wet region. The equilibrium thickness corresponds to the minimum free energy.<br />
<br />
== Pseudo Partial Wetting ==<br />
<br />
When S>0 and A<0 we call this "pseudo" partial wetting<br />
<br />
In this case, the free energy must have a minimum at a certain value of film thickness. Depending on the volume of the drop, two regimes may arise:<br />
<br />
a) microscopic droplet with two possible modes of spreading: <br />
<br />
i) a "pancake" of finite thickness (see figure 3a)<br />
ii) a very dilute gas of molecules expanding indefinitely on the solid (thickness of film =0) (see figure 3b)<br />
<br />
<br />
[[Image:eqn_7.png]]<br />
<br />
<br />
<br />
[[Image:eqn_8.png]]<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_8.png&diff=24079File:Eqn 8.png2012-03-26T13:21:25Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_7.png&diff=24078File:Eqn 7.png2012-03-26T13:20:41Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24077Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:14:26Z<p>Kmiller: /* Complete Wetting */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: eqn_1.png]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn_2.png]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Spread3.png]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
In this case - both A and S are positive and the disjoining pressure (which is the slope of the P(e) versus e function) is monotonically decreasing). <br />
<br />
<br />
[[Image:eqn_4.png]]<br />
<br />
<br />
<br />
A small droplet in contact with a flat, solid surface spreads out and becomes a pancake (depicted below). How thick the film is is determined by the competition long-range forces, which tend to thicken the film, and S, which favors a large wet region. The equilibrium thickness corresponds to the minimum free energy.<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_5.png&diff=24076File:Eqn 5.png2012-03-26T13:08:13Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_4.png&diff=24075File:Eqn 4.png2012-03-26T13:05:51Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24074Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:01:49Z<p>Kmiller: /* Introduction and Fundamental Parameters */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: eqn_1.png]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn_2.png]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Spread3.png]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Spread3.png&diff=24073File:Spread3.png2012-03-26T13:01:09Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24072Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:00:36Z<p>Kmiller: /* Introduction and Fundamental Parameters */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: eqn 1]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn 2]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Eqn 3]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24071Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T13:00:20Z<p>Kmiller: /* Introduction and Fundamental Parameters */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: Eqn 1]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn 2]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Eqn 3]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24070Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T12:58:33Z<p>Kmiller: /* Introduction and Fundamental Parameters */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image: Eqn_1]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image: Eqn_2]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image: Eqn_3]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24069Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T12:58:03Z<p>Kmiller: /* Introduction and Fundamental Parameters */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
Spreading of liquids on ideal smooth solid surfaces can be expressed in terms of free energy per unit area of a film of thickness e: <br />
<br />
[[Image:eqn_1]]<br />
<br />
<br />
<math>\gamma</math> sl and <math>\gamma</math> are the solid/liquid and liquid/air interfacial tensions respectively<br />
<br />
When e is larger than the molecular size, P(e) is controlled by long range van der Waals forces <br />
<br />
When thickness is very large, P(e) goes to zero because the van der Waals forces only act over a certain distance. <br />
<br />
[[Image:eqn_2]]<br />
<br />
A is the difference of the Hamaker constants i.e. A(sl) - A(ll)<br />
<br />
The Hamaker constant is the measure of the strength of a Van der Waals particle-particle interaction. <br />
<br />
For small thicknesses: <br />
<br />
[[Image:eqn_3]]<br />
<br />
<br />
S is the spreading coefficient on a dry solid surface and <math>\gamma</math> so is the surface energy of the dry solid. <br />
<br />
P(e) is not just a function of van der Waals forces - other interactions (dipole-dipole and H bonds for example) may also be important at small thicknesses<br />
<br />
A and S are independent of each other and can be any sign - therefore - there are 4 cases to consider.<br />
<br />
It is important to keep in mind the fact that the energy function P(e) must be convex for the film to be thermodynamically stable.<br />
<br />
== Complete Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_3.png&diff=24068File:Eqn 3.png2012-03-26T12:47:07Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_2.png&diff=24067File:Eqn 2.png2012-03-26T12:46:37Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Eqn_1.png&diff=24066File:Eqn 1.png2012-03-26T12:46:13Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Spreading_of_Nonvolatile_Liquids_in_a_Continuum_Picture&diff=24065Spreading of Nonvolatile Liquids in a Continuum Picture2012-03-26T02:45:07Z<p>Kmiller: New page: == Paper Details == Title: Spreading of Nonvolatile Liquids in a Continuum Picture Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes Journal: Langmuir, 7 (1991), pgs...</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Spreading of Nonvolatile Liquids in a Continuum Picture<br />
<br />
Authors: F. Brochard-Wyart, J.M. di Meglio, D. Quere, P.G. de Gennes<br />
<br />
Journal: Langmuir, 7 (1991), pgs. 335-338<br />
<br />
== Introduction and Fundamental Parameters ==<br />
<br />
This paper focuses on the wetting criteria for solid-liquid interfaces where the long-range interaction is not oscillating and is described by a Hamaker constant (A). The two key parameters are the Hamaker constant and the spreading coefficient (S) which contains contributions from short range interactions. Three fundamental regimes are considered: <br />
<br />
1) Complete wetting - a small droplet spreads to become a flat "pancake" surrounded by a dry solid<br />
<br />
2) Pseudo-partial wetting - a droplet forms a spherical cap with a finite contact angle but - the surrounding solid is "wet" - i.e. the drop is in equilibrium with a molecular film<br />
<br />
3) Partial wetting - the contact angle is nonzero and the solid around the drop is "dry"<br />
<br />
<br />
<br />
<br />
<br />
== Complete Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
== Partial Wetting ==<br />
<br />
<br />
<br />
<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Kelly_Miller&diff=24064Kelly Miller2012-03-26T01:58:09Z<p>Kmiller: </p>
<hr />
<div>Wiki entries for AP226 Capillarity and Wetting (Spring 2012)<br />
<br />
1. Deformable Interfaces<br />
<br />
[[Dynamic Forces Between Two Deformable Oil Droplets in Water]]<br />
<br />
[R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser, "Science"313 (2006): 210-213]<br />
<br />
<br />
2. Capillarity and Gravity<br />
<br />
[[Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer]]<br />
<br />
[C.B. Gorman, H.A. Biebuyck, G.M. Whitesides, "Langmuir" 11 (1995): 2242-2246]<br />
<br />
<br />
3. Long Range Forces<br />
<br />
[[Spreading of Nonvolatile Liquids in a Continuum Picture]]<br />
<br />
[ J.M. di Meglio, D. Quere, P.G. de Gennes, "Langmuir" 7 (1991); 335-338]<br />
<br />
<br />
<br />
<br />
----<br />
----<br />
<br />
<br />
<br />
Wiki entries for AP225 Introduction to Soft Matter (Fall 2011)<br />
<br />
1. Introduction (Week 1):<br />
<br />
[[On The Movement of Small Particles Suspended in Stationary Liquids Required By The Molecular-Kinetic Theory of Heat]]<br />
<br />
[A. Einstein, ''Annalen der Physik'' 17 (1905): 549-560]<br />
<br />
<br />
2. Surface Forces and Disjoining Pressure (Week 2):<br />
<br />
[[Direct Measurement of Molecular Forces]]<br />
<br />
[B.V. Berjaguin, Y.I. Rabinovich, ''Nature'' 272 (1978): 313-318]<br />
<br />
<br />
3. Capillary and Wetting (Weeks 3 & 4)<br />
<br />
[[Thermodynamic deviations of the mechanical equilibrium conditions for fluid surfaces: Young's and Laplace's equations]]<br />
<br />
[P. Roura, "American Journal of Physics" 73 (12), (2005): 1139-1147<br />
<br />
<br />
4. Polymers (Weeks 5 &6)<br />
<br />
[[A Blind Spot in Confocal Reflection Microscopy: The Dependence of Fiber Brightness on Fiber Orientation in Imaging Biopolymer Networks]]<br />
<br />
[Jawerth, L.M., "Biophysical Journal" 98, (2009): L01-L03]<br />
<br />
<br />
5. Surfactants (Week 7)<br />
<br />
[[Krafft Points, Critical Micelle Concentrations, Surface Tension, and Solubilizing Power of Aqueous Solutions of Fluorinated Surfactants]]<br />
<br />
[Kunleda, Shinoda; The Journal of Physical Chemistry, Vol. 80, No. 22, 1976]<br />
<br />
<br />
6. Phases and phase diagrams (Week 8)<br />
<br />
[[Understanding Foods as Soft Materials]]<br />
<br />
[Mezzenga, R., Schurtenberger, A., Burbidge, A., Michel, M.; Nature Materials, Vol. 4, 2005]<br />
<br />
<br />
<br />
7. Charged Interfaces<br />
<br />
[[Hydrodynamics within the Electric Double Layer on Slipping Surfaces]]<br />
<br />
[Laurent J., Ybert, C., Trizac, E., Bocquet, L., Physical Review Letters, 93 (25), 2004]<br />
<br />
<br />
<br />
8. Thin "Soft" Films and Colloidal Stability<br />
<br />
[[A public study of the lifetime distribution of soap films]]<br />
<br />
[Tobin, S.T., Meagher, A.J., Bulfin, B., Mobius, M., Hutzler, S., American Journal of Physics, 79(8) 2011, pp. 819]</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Kelly_Miller&diff=24063Kelly Miller2012-03-26T01:57:25Z<p>Kmiller: </p>
<hr />
<div>Wiki entries for AP226 Capillarity and Wetting (Spring 2012)<br />
<br />
1. Deformable Interfaces<br />
<br />
[[Dynamic Forces Between Two Deformable Oil Droplets in Water]]<br />
<br />
[R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser, "Science"313 (2006): 210-213]<br />
<br />
<br />
2. Capillarity and Gravity<br />
<br />
[[Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer]]<br />
<br />
[C.B. Gorman, H.A. Biebuyck, G.M. Whitesides, "Langmuir" 11 (1995): 2242-2246]<br />
<br />
<br />
3. Long Range Forces<br />
<br />
[[Spreading of Nonvolatile Liquids in a Continuum Picture]]<br />
<br />
[ J.M. di Meglio, D. Quere, P.G. de Gennes, "Langmuir" 7 (1991); 335-338]<br />
<br />
<br />
Wiki entries for AP225 Introduction to Soft Matter (Fall 2011)<br />
<br />
1. Introduction (Week 1):<br />
<br />
[[On The Movement of Small Particles Suspended in Stationary Liquids Required By The Molecular-Kinetic Theory of Heat]]<br />
<br />
[A. Einstein, ''Annalen der Physik'' 17 (1905): 549-560]<br />
<br />
<br />
2. Surface Forces and Disjoining Pressure (Week 2):<br />
<br />
[[Direct Measurement of Molecular Forces]]<br />
<br />
[B.V. Berjaguin, Y.I. Rabinovich, ''Nature'' 272 (1978): 313-318]<br />
<br />
<br />
3. Capillary and Wetting (Weeks 3 & 4)<br />
<br />
[[Thermodynamic deviations of the mechanical equilibrium conditions for fluid surfaces: Young's and Laplace's equations]]<br />
<br />
[P. Roura, "American Journal of Physics" 73 (12), (2005): 1139-1147<br />
<br />
<br />
4. Polymers (Weeks 5 &6)<br />
<br />
[[A Blind Spot in Confocal Reflection Microscopy: The Dependence of Fiber Brightness on Fiber Orientation in Imaging Biopolymer Networks]]<br />
<br />
[Jawerth, L.M., "Biophysical Journal" 98, (2009): L01-L03]<br />
<br />
<br />
5. Surfactants (Week 7)<br />
<br />
[[Krafft Points, Critical Micelle Concentrations, Surface Tension, and Solubilizing Power of Aqueous Solutions of Fluorinated Surfactants]]<br />
<br />
[Kunleda, Shinoda; The Journal of Physical Chemistry, Vol. 80, No. 22, 1976]<br />
<br />
<br />
6. Phases and phase diagrams (Week 8)<br />
<br />
[[Understanding Foods as Soft Materials]]<br />
<br />
[Mezzenga, R., Schurtenberger, A., Burbidge, A., Michel, M.; Nature Materials, Vol. 4, 2005]<br />
<br />
<br />
<br />
7. Charged Interfaces<br />
<br />
[[Hydrodynamics within the Electric Double Layer on Slipping Surfaces]]<br />
<br />
[Laurent J., Ybert, C., Trizac, E., Bocquet, L., Physical Review Letters, 93 (25), 2004]<br />
<br />
<br />
<br />
8. Thin "Soft" Films and Colloidal Stability<br />
<br />
[[A public study of the lifetime distribution of soap films]]<br />
<br />
[Tobin, S.T., Meagher, A.J., Bulfin, B., Mobius, M., Hutzler, S., American Journal of Physics, 79(8) 2011, pp. 819]</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24062Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T01:51:38Z<p>Kmiller: /* Conclusion */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution (see figure below). <br />
<br />
<br />
[[Image:setup.png]]<br />
<br />
<br />
The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:contact.png]]<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
A drop of HDT on transparent gold was shown to be able to behave as a planar convex lens. A drop on the surface at -1.7 V will focus light transmitted through it (see figure 4 below). <br />
<br />
[[Image:lens.png]]<br />
<br />
<br />
<br />
<br />
The images in figure 4 show that the drop can act as an optical switch that will focus and defocus light or an image in the far field as a function of an applied electrical potential. In Figure 4c - the drop could be electrochemically perturbed to bring an image repeatedly into and out of focus. <br />
<br />
The focal length of the planar convex lens (that is formed by the drop) is proportional to its radius of curvature such that f= r/ <math>\delta</math> n where r is the radius of curvature and <math>\delta</math> n is the difference in refractive indices between the two media<br />
<br />
<br />
<br />
The size and shape of the drops under the aqueous electrolyte can be controlled with specific types of spatially patterned self-assembled monolayers. The gold surface is patterned with HDT using "microcontact printing". The patterned surface is moved through a think layer of HDT on top of aqueous electrolyte which causes the drops of HDT to self-assemble on the hydrophobic regions of the patterned SAM. By lowering the potential of the substrate - the shape of the drops changes and the focal point of light transmitted through each microlens changes.<br />
<br />
== Conclusion ==<br />
<br />
Self-assembly of drops on surfaces can be directed by patterned SAM's. When the electrochemical potential is changed, the entire pattern of SAM's are desorbed reductively from the surface. Drops were seen to remain on the regions of the surface that were originally patterned with HDT. The experiments conducted in this paper show how an electrical potential can be used to influence the shape of a drop in a reversible way. This has applications in making liquid lenses and arrays of lenses whose focal lengths can be changed by changing the potential. Patterned self-assembly can be used to make arrays of drops of specific size, shape and organization. Drops of HDT could be used an electroactive switches to control the coupling of light to a detector.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24061Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T01:30:13Z<p>Kmiller: /* Analysis */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution (see figure below). <br />
<br />
<br />
[[Image:setup.png]]<br />
<br />
<br />
The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:contact.png]]<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
A drop of HDT on transparent gold was shown to be able to behave as a planar convex lens. A drop on the surface at -1.7 V will focus light transmitted through it (see figure 4 below). <br />
<br />
[[Image:lens.png]]<br />
<br />
<br />
<br />
<br />
The images in figure 4 show that the drop can act as an optical switch that will focus and defocus light or an image in the far field as a function of an applied electrical potential. In Figure 4c - the drop could be electrochemically perturbed to bring an image repeatedly into and out of focus. <br />
<br />
The focal length of the planar convex lens (that is formed by the drop) is proportional to its radius of curvature such that f= r/ <math>\delta</math> n where r is the radius of curvature and <math>\delta</math> n is the difference in refractive indices between the two media<br />
<br />
<br />
<br />
The size and shape of the drops under the aqueous electrolyte can be controlled with specific types of spatially patterned self-assembled monolayers. The gold surface is patterned with HDT using "microcontact printing". The patterned surface is moved through a think layer of HDT on top of aqueous electrolyte which causes the drops of HDT to self-assemble on the hydrophobic regions of the patterned SAM. By lowering the potential of the substrate - the shape of the drops changes and the focal point of light transmitted through each microlens changes.<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24060Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T01:03:31Z<p>Kmiller: /* Experiment */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution (see figure below). <br />
<br />
<br />
[[Image:setup.png]]<br />
<br />
<br />
The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:contact.png]]<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
A drop of HDT on transparent gold was shown to be able to behave as a planar convex lens. A drop on the surface at -1.7 V will focus light transmitted through it (see figure 4 below). <br />
<br />
[[Image:lens.png]]<br />
<br />
<br />
<br />
<br />
The images in figure 4 show that the drop can act as an optical switch that will focus and defocus light or an image in the far field as a function of an applied electrical potential. In Figure 4c - the drop could be electrochemically perturbed to bring an image repeatedly into and out of focus. <br />
<br />
The focal length of the planar convex lens (that is formed by the drop) is proportional to its radius of curvature such that f= r/ <math>\delta</math> n where r is the radius of curvature and <math>\delta</math> n is the difference in refractive indices between the two media<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24059Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T01:02:11Z<p>Kmiller: /* Experiment */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution (see figure below). The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:setup.png]]<br />
[[Image:contact.png]]<br />
<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
A drop of HDT on transparent gold was shown to be able to behave as a planar convex lens. A drop on the surface at -1.7 V will focus light transmitted through it (see figure 4 below). <br />
<br />
[[Image:lens.png]]<br />
<br />
<br />
<br />
<br />
The images in figure 4 show that the drop can act as an optical switch that will focus and defocus light or an image in the far field as a function of an applied electrical potential. In Figure 4c - the drop could be electrochemically perturbed to bring an image repeatedly into and out of focus. <br />
<br />
The focal length of the planar convex lens (that is formed by the drop) is proportional to its radius of curvature such that f= r/ <math>\delta</math> n where r is the radius of curvature and <math>\delta</math> n is the difference in refractive indices between the two media<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24058Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T00:59:52Z<p>Kmiller: /* Analysis */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution. The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:contact.png]]<br />
<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
A drop of HDT on transparent gold was shown to be able to behave as a planar convex lens. A drop on the surface at -1.7 V will focus light transmitted through it (see figure 4 below). <br />
<br />
[[Image:lens.png]]<br />
<br />
<br />
<br />
<br />
The images in figure 4 show that the drop can act as an optical switch that will focus and defocus light or an image in the far field as a function of an applied electrical potential. In Figure 4c - the drop could be electrochemically perturbed to bring an image repeatedly into and out of focus. <br />
<br />
The focal length of the planar convex lens (that is formed by the drop) is proportional to its radius of curvature such that f= r/ <math>\delta</math> n where r is the radius of curvature and <math>\delta</math> n is the difference in refractive indices between the two media<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24057Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T00:59:14Z<p>Kmiller: /* Analysis */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution. The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:contact.png]]<br />
<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
A drop of HDT on transparent gold was shown to be able to behave as a planar convex lens. A drop on the surface at -1.7 V will focus light transmitted through it (see figure 4 below). <br />
<br />
[[Image:setup.png]]<br />
<br />
<br />
<br />
<br />
The images in figure 4 show that the drop can act as an optical switch that will focus and defocus light or an image in the far field as a function of an applied electrical potential. In Figure 4c - the drop could be electrochemically perturbed to bring an image repeatedly into and out of focus. <br />
<br />
The focal length of the planar convex lens (that is formed by the drop) is proportional to its radius of curvature such that f= r/ <math>\delta</math> n where r is the radius of curvature and <math>\delta</math> n is the difference in refractive indices between the two media<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Lens.png&diff=24056File:Lens.png2012-03-26T00:53:49Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Setup.png&diff=24055File:Setup.png2012-03-26T00:53:28Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24054Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T00:49:08Z<p>Kmiller: /* Experiment */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
A drop of HDT was placed on a gold surface under an aqueous electrolyte solution. The drop spread reactively on gold at 0 V (relative to the silver electrode) and formed a hydrophobic monolayer under the drop. the advancing contact angle of this drop reached a value of ~37 degrees (see figure 1 below). When the potential of the gold was switched to -1.7V, the SAM underwent electrodesorption and the drop retracted. The contact angle of the drop as it receded was ~ 128 degrees. As the hydrophobic SAM desorbed and water wet the resulting charged gold surface, the drop retracted on the surface. When the drop retracted, this also reduced the interfacial area between the drop and the water. <br />
<br />
<br />
[[Image:contact.png]]<br />
<br />
<br />
<br />
The drop's contact angle changed continuously as a function of the potential between these two limiting values (see figure 2). Figure 2 shows hysteresis in the contact angles of the spreading/retraction which did not change with the thickness of the gold or with the chain length of the thiol. <br />
<br />
<br />
[[Image:hysteresis.png]]<br />
<br />
<br />
<br />
<br />
<br />
The switching speeds for drops were determined by changing the potential of the gold (-1.7 V for retraction of drop and 0V for spreading of the drop) and then observing he time required for the shape to change by taking a video.<br />
<br />
== Analysis ==<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Hysteresis.png&diff=24053File:Hysteresis.png2012-03-26T00:46:43Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=File:Contact.png&diff=24052File:Contact.png2012-03-26T00:41:52Z<p>Kmiller: </p>
<hr />
<div></div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24051Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-26T00:29:31Z<p>Kmiller: /* Introduction */</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
The focus of this paper is describing how the contact angle of drops of liquid can be controlled and varied using an applied electrical potential. The drops could act as lenses and could be used an an optical switch which focuses/ defocuses light. <br />
<br />
The electrical potential used to control the contact angles is applied across a self-assembled monolayer (SAM) on a gold surface. The drops described in this paper are hexadecanethiol (HDT). When the gold was transparent, the drops acted as lenses for transmitting light. The liquid HDT drops resting on a gold surface and surrounded by aqueous electrolyte - act like lenses whose shape can be quickly, reproducibly and reversibly changed by applying a potential to the substrate supporting the drops.<br />
<br />
== Experiment ==<br />
<br />
<br />
== Analysis ==<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Kelly_Miller&diff=24050Kelly Miller2012-03-26T00:14:37Z<p>Kmiller: </p>
<hr />
<div>Wiki entries for AP226 Capillarity and Wetting (Spring 2012)<br />
<br />
1. Deformable Interfaces<br />
<br />
<br />
[[Dynamic Forces Between Two Deformable Oil Droplets in Water]]<br />
<br />
[R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser, "Science"313 (2006): 210-213]<br />
<br />
<br />
2. Capillarity and Gravity<br />
<br />
[[Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer]]<br />
<br />
[C.B. Gorman, H.A. Biebuyck, G.M. Whitesides, "Langmuir" 11 (1995): 2242-2246]<br />
<br />
<br />
Wiki entries for AP225 Introduction to Soft Matter (Fall 2011)<br />
<br />
1. Introduction (Week 1):<br />
<br />
[[On The Movement of Small Particles Suspended in Stationary Liquids Required By The Molecular-Kinetic Theory of Heat]]<br />
<br />
[A. Einstein, ''Annalen der Physik'' 17 (1905): 549-560]<br />
<br />
<br />
2. Surface Forces and Disjoining Pressure (Week 2):<br />
<br />
[[Direct Measurement of Molecular Forces]]<br />
<br />
[B.V. Berjaguin, Y.I. Rabinovich, ''Nature'' 272 (1978): 313-318]<br />
<br />
<br />
3. Capillary and Wetting (Weeks 3 & 4)<br />
<br />
[[Thermodynamic deviations of the mechanical equilibrium conditions for fluid surfaces: Young's and Laplace's equations]]<br />
<br />
[P. Roura, "American Journal of Physics" 73 (12), (2005): 1139-1147<br />
<br />
<br />
4. Polymers (Weeks 5 &6)<br />
<br />
[[A Blind Spot in Confocal Reflection Microscopy: The Dependence of Fiber Brightness on Fiber Orientation in Imaging Biopolymer Networks]]<br />
<br />
[Jawerth, L.M., "Biophysical Journal" 98, (2009): L01-L03]<br />
<br />
<br />
5. Surfactants (Week 7)<br />
<br />
[[Krafft Points, Critical Micelle Concentrations, Surface Tension, and Solubilizing Power of Aqueous Solutions of Fluorinated Surfactants]]<br />
<br />
[Kunleda, Shinoda; The Journal of Physical Chemistry, Vol. 80, No. 22, 1976]<br />
<br />
<br />
6. Phases and phase diagrams (Week 8)<br />
<br />
[[Understanding Foods as Soft Materials]]<br />
<br />
[Mezzenga, R., Schurtenberger, A., Burbidge, A., Michel, M.; Nature Materials, Vol. 4, 2005]<br />
<br />
<br />
<br />
7. Charged Interfaces<br />
<br />
[[Hydrodynamics within the Electric Double Layer on Slipping Surfaces]]<br />
<br />
[Laurent J., Ybert, C., Trizac, E., Bocquet, L., Physical Review Letters, 93 (25), 2004]<br />
<br />
<br />
<br />
8. Thin "Soft" Films and Colloidal Stability<br />
<br />
[[A public study of the lifetime distribution of soap films]]<br />
<br />
[Tobin, S.T., Meagher, A.J., Bulfin, B., Mobius, M., Hutzler, S., American Journal of Physics, 79(8) 2011, pp. 819]</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Control_of_the_Shape_of_Liquid_Lenses_on_a_Modified_Gold_Surface_Using_as_Applied_Electrical_Potential_across_a_Self-Assembled_Monolayer&diff=24049Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer2012-03-23T13:12:11Z<p>Kmiller: New page: == Paper Details == Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer Authors: C.B. Gorman,...</p>
<hr />
<div><br />
== Paper Details ==<br />
<br />
Title: Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer<br />
<br />
Authors: C.B. Gorman, H.A. Biebuyck, G.M. Whitesides<br />
<br />
Journal: Langmuir 11 (1995) pgs. 2242-2246<br />
<br />
<br />
== Introduction ==<br />
<br />
<br />
== Experiment ==<br />
<br />
<br />
== Analysis ==<br />
<br />
<br />
== Conclusion ==</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Kelly_Miller&diff=24048Kelly Miller2012-03-23T13:08:58Z<p>Kmiller: </p>
<hr />
<div>Wiki entries for AP226 Capillarity and Wetting (Spring 2012)<br />
<br />
1. Deformable Interfaces<br />
<br />
<br />
[[Dynamic Forces Between Two Deformable Oil Droplets in Water]]<br />
<br />
[R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser, "Science"313 (2006): 210-213]<br />
<br />
2. Capillarity and Gravity<br />
<br />
[[Control of the Shape of Liquid Lenses on a Modified Gold Surface Using as Applied Electrical Potential across a Self-Assembled Monolayer]]<br />
<br />
[C.B. Gorman, H.A. Biebuyck, G.M. Whitesides, "Langmuir" 11 (1995): 2242-2246]<br />
<br />
<br />
Wiki entries for AP225 Introduction to Soft Matter (Fall 2011)<br />
<br />
1. Introduction (Week 1):<br />
<br />
[[On The Movement of Small Particles Suspended in Stationary Liquids Required By The Molecular-Kinetic Theory of Heat]]<br />
<br />
[A. Einstein, ''Annalen der Physik'' 17 (1905): 549-560]<br />
<br />
<br />
2. Surface Forces and Disjoining Pressure (Week 2):<br />
<br />
[[Direct Measurement of Molecular Forces]]<br />
<br />
[B.V. Berjaguin, Y.I. Rabinovich, ''Nature'' 272 (1978): 313-318]<br />
<br />
<br />
3. Capillary and Wetting (Weeks 3 & 4)<br />
<br />
[[Thermodynamic deviations of the mechanical equilibrium conditions for fluid surfaces: Young's and Laplace's equations]]<br />
<br />
[P. Roura, "American Journal of Physics" 73 (12), (2005): 1139-1147<br />
<br />
<br />
4. Polymers (Weeks 5 &6)<br />
<br />
[[A Blind Spot in Confocal Reflection Microscopy: The Dependence of Fiber Brightness on Fiber Orientation in Imaging Biopolymer Networks]]<br />
<br />
[Jawerth, L.M., "Biophysical Journal" 98, (2009): L01-L03]<br />
<br />
<br />
5. Surfactants (Week 7)<br />
<br />
[[Krafft Points, Critical Micelle Concentrations, Surface Tension, and Solubilizing Power of Aqueous Solutions of Fluorinated Surfactants]]<br />
<br />
[Kunleda, Shinoda; The Journal of Physical Chemistry, Vol. 80, No. 22, 1976]<br />
<br />
<br />
6. Phases and phase diagrams (Week 8)<br />
<br />
[[Understanding Foods as Soft Materials]]<br />
<br />
[Mezzenga, R., Schurtenberger, A., Burbidge, A., Michel, M.; Nature Materials, Vol. 4, 2005]<br />
<br />
<br />
<br />
7. Charged Interfaces<br />
<br />
[[Hydrodynamics within the Electric Double Layer on Slipping Surfaces]]<br />
<br />
[Laurent J., Ybert, C., Trizac, E., Bocquet, L., Physical Review Letters, 93 (25), 2004]<br />
<br />
<br />
<br />
8. Thin "Soft" Films and Colloidal Stability<br />
<br />
[[A public study of the lifetime distribution of soap films]]<br />
<br />
[Tobin, S.T., Meagher, A.J., Bulfin, B., Mobius, M., Hutzler, S., American Journal of Physics, 79(8) 2011, pp. 819]</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Dynamic_Forces_Between_Two_Deformable_Oil_Droplets_in_Water&diff=24047Dynamic Forces Between Two Deformable Oil Droplets in Water2012-03-23T03:39:28Z<p>Kmiller: /* Experiment */</p>
<hr />
<div>== Information ==<br />
<br />
Title: Dynamic Forces Between Two Deformable Oil Droplets in Water<br />
<br />
Authors: R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser<br />
<br />
Journal: Science, 313 (2006): 210-213 <br />
<br />
<br />
== Keywords ==<br />
<br />
dynamic forces, colloidal suspensions, interfacial deformation, static surface forces<br />
<br />
<br />
== Introduction ==<br />
<br />
Interactions between static surfaces are well studied, however, dynamic interactions in biological and other suspended soft-matter systems is still not completely understood. Dynamic forces are key to manipulating and controlling soft-matter systems (such as emulsions and complex fluids). Understanding dynamic droplet-droplet interactions is very challenging. This paper presents the dynamic interactions between two deformable oil droplets. The methodology presented in the paper is widely applicable to all soft-matter systems and has important implications for studying collision forces from Brownian motion. <br />
<br />
Dynamic interactions between soft matter particles, such as emulsion droplets, is difficult because every interface in deformable. Recently, studies have demonstrated direct force measurements of interactions between droplets with radii of around 40 microns (intermediate size droplets). This study focusses on developing a model for droplet-droplet interactions for intermediate size droplets where deformation, hydrodynamic drainage, and interaction forces are all important. This study also shows how traditional concepts of drainage as a two-stage process are not appropriate for droplet sizes relevant to emulsions. <br />
<br />
<br />
== Experiment ==<br />
<br />
Two decane droplets with radii of 43 and 90 microns, in a surfactant solution, were immobilized on an AFM cantilever and substrate. The dynamic interaction force between the droplets was measured as a function of piezo drive motion of the substrate (see figure 1)<br />
<br />
[[Image:droplet.png]]<br />
<br />
<br />
<br />
<br />
<br />
A) the experiment between two oil droplets - one immobilized on the cantilever and the other immobilized on the substrate of an AFM<br />
<br />
B - D) The dynamic interaction force (F) versus piezo drive motion (X) between two oil droplets in aqueous solution. The points refer to the experimental data and the solid lines are the calculated force curves from a model of the dynamic droplet interactions. The open symbols refer to approach velocities and the filled symbols refer to retract velocities.<br />
<br />
The velocity range spans the likely velocities of an emulsion droplet of comparable size when undergoing Brownian motion. The measurements show that hydrodynamic interactions between droplets of this size are important even when describing emulsion stability, where equilibrium forces are assumed to dominate.<br />
<br />
== Analysis ==<br />
<br />
A quantitative analysis of the data to determine the interfacial separation is based on the Young-Laplace equation and the techniques developed for static force measurements between a rigid particle and droplet. <br />
<br />
The dynamic problem contains three disparate length scales: <br />
<br />
1) droplet radii (~ 50 microns)<br />
<br />
2) the axial length scale of interaction forces (10-100nm)<br />
<br />
3) radial length scale of the interaction (1-5 microns)<br />
<br />
Two PDE were used in the analysis - the Reynolds drainage equation and the normal stress balance: <br />
<br />
[[Image:drainage.png]]<br />
<br />
<br />
h(r,t) is the interdroplet separation, p is the hydrodynamic pressure, <math>\Pi</math> is the equilibrium disjoining pressure, Ro is the unperturbed droplet radii<br />
<br />
The disjoining pressure was calculated using the Poisson-Boltzmann equation to describe the electrostatic double-layer repulsion between the negatively charged surfactant-laden interfaces. This required a surface potential for the system to be known. <br />
<br />
<br />
== Conclusion ==<br />
<br />
<br />
In a dynamic system, the droplets flatten whenever the normal pressure is on the order of the droplet Laplace pressure - regardless of the contribution to the pressure from either equilibrium surface forces or hydrodynamic drainage. The total radial pressure profile changes as a function of radii - for small radii the radial pressure is positive and for larger radii, it is negative. This is due to the combination of pressure with different length scales from a positive equilibrium surface force at these interfacial separations and the negative hydrodynamic drainage pressure. Unlike the case involving only equilibrium interactions, for the dynamic interaction, droplet coalescence can occur as the droplets more apart. <br />
<br />
This paper demonstrated how the interactions for dynamic droplets in the 50-100 micron range are much more complicated than for the interactions of static droplets of the same size - hydrodynamic forces and surface forces are coupled. The relative length scales that the forces act over are very important and will influence which force dominates the interaction.</div>Kmillerhttp://soft-matter.seas.harvard.edu/index.php?title=Dynamic_Forces_Between_Two_Deformable_Oil_Droplets_in_Water&diff=24046Dynamic Forces Between Two Deformable Oil Droplets in Water2012-03-23T03:39:05Z<p>Kmiller: /* Experiment */</p>
<hr />
<div>== Information ==<br />
<br />
Title: Dynamic Forces Between Two Deformable Oil Droplets in Water<br />
<br />
Authors: R.R. Dagastine, R. Manica, S.L. Carnier, D.Y.C. Chan, G.W. Stevens, and F. Grieser<br />
<br />
Journal: Science, 313 (2006): 210-213 <br />
<br />
<br />
== Keywords ==<br />
<br />
dynamic forces, colloidal suspensions, interfacial deformation, static surface forces<br />
<br />
<br />
== Introduction ==<br />
<br />
Interactions between static surfaces are well studied, however, dynamic interactions in biological and other suspended soft-matter systems is still not completely understood. Dynamic forces are key to manipulating and controlling soft-matter systems (such as emulsions and complex fluids). Understanding dynamic droplet-droplet interactions is very challenging. This paper presents the dynamic interactions between two deformable oil droplets. The methodology presented in the paper is widely applicable to all soft-matter systems and has important implications for studying collision forces from Brownian motion. <br />
<br />
Dynamic interactions between soft matter particles, such as emulsion droplets, is difficult because every interface in deformable. Recently, studies have demonstrated direct force measurements of interactions between droplets with radii of around 40 microns (intermediate size droplets). This study focusses on developing a model for droplet-droplet interactions for intermediate size droplets where deformation, hydrodynamic drainage, and interaction forces are all important. This study also shows how traditional concepts of drainage as a two-stage process are not appropriate for droplet sizes relevant to emulsions. <br />
<br />
<br />
== Experiment ==<br />
<br />
Two decane droplets with radii of 43 and 90 microns, in a surfactant solution, were immobilized on an AFM cantilever and substrate. The dynamic interaction force between the droplets was measured as a function of piezo drive motion of the substrate (see figure 1)<br />
<br />
[[Image:droplet.png]]<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
A) the experiment between two oil droplets - one immobilized on the cantilever and the other immobilized on the substrate of an AFM<br />
<br />
B - D) The dynamic interaction force (F) versus piezo drive motion (X) between two oil droplets in aqueous solution. The points refer to the experimental data and the solid lines are the calculated force curves from a model of the dynamic droplet interactions. The open symbols refer to approach velocities and the filled symbols refer to retract velocities.<br />
<br />
The velocity range spans the likely velocities of an emulsion droplet of comparable size when undergoing Brownian motion. The measurements show that hydrodynamic interactions between droplets of this size are important even when describing emulsion stability, where equilibrium forces are assumed to dominate. <br />
<br />
<br />
<br />
== Analysis ==<br />
<br />
A quantitative analysis of the data to determine the interfacial separation is based on the Young-Laplace equation and the techniques developed for static force measurements between a rigid particle and droplet. <br />
<br />
The dynamic problem contains three disparate length scales: <br />
<br />
1) droplet radii (~ 50 microns)<br />
<br />
2) the axial length scale of interaction forces (10-100nm)<br />
<br />
3) radial length scale of the interaction (1-5 microns)<br />
<br />
Two PDE were used in the analysis - the Reynolds drainage equation and the normal stress balance: <br />
<br />
[[Image:drainage.png]]<br />
<br />
<br />
h(r,t) is the interdroplet separation, p is the hydrodynamic pressure, <math>\Pi</math> is the equilibrium disjoining pressure, Ro is the unperturbed droplet radii<br />
<br />
The disjoining pressure was calculated using the Poisson-Boltzmann equation to describe the electrostatic double-layer repulsion between the negatively charged surfactant-laden interfaces. This required a surface potential for the system to be known. <br />
<br />
<br />
== Conclusion ==<br />
<br />
<br />
In a dynamic system, the droplets flatten whenever the normal pressure is on the order of the droplet Laplace pressure - regardless of the contribution to the pressure from either equilibrium surface forces or hydrodynamic drainage. The total radial pressure profile changes as a function of radii - for small radii the radial pressure is positive and for larger radii, it is negative. This is due to the combination of pressure with different length scales from a positive equilibrium surface force at these interfacial separations and the negative hydrodynamic drainage pressure. Unlike the case involving only equilibrium interactions, for the dynamic interaction, droplet coalescence can occur as the droplets more apart. <br />
<br />
This paper demonstrated how the interactions for dynamic droplets in the 50-100 micron range are much more complicated than for the interactions of static droplets of the same size - hydrodynamic forces and surface forces are coupled. The relative length scales that the forces act over are very important and will influence which force dominates the interaction.</div>Kmiller