Difference between revisions of "Uni-directional liquid spreading on asymmetric nanostructured surfaces"

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(New page: Title: Uni-directional liquid spreading on asymmetric nanostructured surfaces Reference: E.N. Wang, K.-H. Chu, R. Xiao G.C. Rutledge, G.H. McKinley, “Science” 318, 1618 (2007). ==So...)
 
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Title: Uni-directional liquid spreading on asymmetric nanostructured surfaces
 
Title: Uni-directional liquid spreading on asymmetric nanostructured surfaces
  
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Controlling surface wettability and liquid spreading on patterned surfaces is of significant interest for a broad range of applications, including DNA microarrays, digital lab-on-a-chip, anti-fogging and fog-harvesting, inkjet printing and thin-film lubrication. Advancements in surface engineering, with the fabrication of various micro/nanoscale topographic features, and selective chemical patterning on surfaces have enhanced surface wettability and enabled control of the liquid film thickness and final wetted shape. In addition, groove geometries and patterned surface chemistries have produced anisotropic wetting, where contact-angle variations in different directions resulted in elongated droplet shapes. In all of these studies, however, the wetting behavior preserves left–right symmetry. Here, we demonstrate that we can harness the design of asymmetric nanostructured surfaces to achieve uni-directional liquid spreading, where the liquid propagates in a single preferred direction and pins in all others. Through experiments and modelling, we determined that the spreading characteristic is dependent on the degree of nanostructure asymmetry, the height-to-spacing ratio of the nanostructures and the intrinsic contact angle. The theory, based on an energy argument, provides excellent agreement with experimental data. The insights gained from this work offer new opportunities to tailor advanced nanostructures to achieve active control of complex flow patterns and wetting on demand.  
 
Controlling surface wettability and liquid spreading on patterned surfaces is of significant interest for a broad range of applications, including DNA microarrays, digital lab-on-a-chip, anti-fogging and fog-harvesting, inkjet printing and thin-film lubrication. Advancements in surface engineering, with the fabrication of various micro/nanoscale topographic features, and selective chemical patterning on surfaces have enhanced surface wettability and enabled control of the liquid film thickness and final wetted shape. In addition, groove geometries and patterned surface chemistries have produced anisotropic wetting, where contact-angle variations in different directions resulted in elongated droplet shapes. In all of these studies, however, the wetting behavior preserves left–right symmetry. Here, we demonstrate that we can harness the design of asymmetric nanostructured surfaces to achieve uni-directional liquid spreading, where the liquid propagates in a single preferred direction and pins in all others. Through experiments and modelling, we determined that the spreading characteristic is dependent on the degree of nanostructure asymmetry, the height-to-spacing ratio of the nanostructures and the intrinsic contact angle. The theory, based on an energy argument, provides excellent agreement with experimental data. The insights gained from this work offer new opportunities to tailor advanced nanostructures to achieve active control of complex flow patterns and wetting on demand.  
 
==Soft matter example==
 
==Soft matter example==
[[Image:Fig 1 (Fig 1_Wang_side profile).jpg|thumb|right|300px| '''Fig. 1'''. | Comparison of wetting behaviour on symmetric and asymmetric nanostructured surfaces. The top image shows the symmetric liquid spreading of a 1 µl droplet of water on typical vertical nanopillars. The bottom image shows the uni-directional liquid spreading of a droplet on the same nanostructures as the top image, but with a 12◦ deflection angle. Insets are the SEM images of the upright and bent posts, respectively, with scale bars at 10 µm.]]
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[[Image:Fig 1 (Fig 1_Wang_side profile).jpg|thumb|right|300px| '''Fig. 1'''. | Side view comparison of wetting behavior on symmetric and asymmetric nanostructured surfaces. The top image shows the symmetric liquid spreading of a 1 µl droplet of water on typical vertical nanopillars. The bottom image shows the uni-directional liquid spreading of a droplet on the same nanostructures as the top image, but with a 12◦ deflection angle. Insets are the SEM images of the upright and bent posts, respectively, with scale bars at 10 µm.]]
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[[Image:Fig 2 (Fig 2_Wang_top profile).jpg|thumb|left|300px| '''Fig. 2'''. | Top view comparison of wetting behavior on symmetric and asymmetric nanostructured surfaces. The top image shows the symmetric liquid spreading of a 1 µl droplet of water on typical vertical nanopillars. The bottom image shows the uni-directional liquid spreading of a droplet on the same nanostructures as the top image, but with a 12◦ deflection angle.]]

Revision as of 17:18, 6 October 2010

Title: Uni-directional liquid spreading on asymmetric nanostructured surfaces

Reference: E.N. Wang, K.-H. Chu, R. Xiao G.C. Rutledge, G.H. McKinley, “Science” 318, 1618 (2007).

Soft matter keywords

asymmetry, contact angle, hydrophocitiy, hysteresis , nanopillars, wetting

Abstract from the original paper

Controlling surface wettability and liquid spreading on patterned surfaces is of significant interest for a broad range of applications, including DNA microarrays, digital lab-on-a-chip, anti-fogging and fog-harvesting, inkjet printing and thin-film lubrication. Advancements in surface engineering, with the fabrication of various micro/nanoscale topographic features, and selective chemical patterning on surfaces have enhanced surface wettability and enabled control of the liquid film thickness and final wetted shape. In addition, groove geometries and patterned surface chemistries have produced anisotropic wetting, where contact-angle variations in different directions resulted in elongated droplet shapes. In all of these studies, however, the wetting behavior preserves left–right symmetry. Here, we demonstrate that we can harness the design of asymmetric nanostructured surfaces to achieve uni-directional liquid spreading, where the liquid propagates in a single preferred direction and pins in all others. Through experiments and modelling, we determined that the spreading characteristic is dependent on the degree of nanostructure asymmetry, the height-to-spacing ratio of the nanostructures and the intrinsic contact angle. The theory, based on an energy argument, provides excellent agreement with experimental data. The insights gained from this work offer new opportunities to tailor advanced nanostructures to achieve active control of complex flow patterns and wetting on demand.

Soft matter example

Side view comparison of wetting behavior on symmetric and asymmetric nanostructured surfaces. The top image shows the symmetric liquid spreading of a 1 µl droplet of water on typical vertical nanopillars. The bottom image shows the uni-directional liquid spreading of a droplet on the same nanostructures as the top image, but with a 12◦ deflection angle. Insets are the SEM images of the upright and bent posts, respectively, with scale bars at 10 µm.


Top view comparison of wetting behavior on symmetric and asymmetric nanostructured surfaces. The top image shows the symmetric liquid spreading of a 1 µl droplet of water on typical vertical nanopillars. The bottom image shows the uni-directional liquid spreading of a droplet on the same nanostructures as the top image, but with a 12◦ deflection angle.