Difference between revisions of "Phase Behavior and Rheology of Attractive Rod Like Particles"

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(Summary)
(Summary)
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== Summary ==
 
== Summary ==
Huang, Rotstein, Fraden, Kasza, and Flynn study an aqueous solution of rod-shaped particles to look for transitions between isotropic, nematic, liquid, and gel states. The transitions are a function of particle concentration, temperature, and salt concentration in the water. For this experiment, Huang ''et al.'' create particles by coating bacteriofage fd with poly(N-isopropylacrylamide) (PNIPAM). The researchers use both rheological measurements and light scattering measurements to characterize the solutions which do not agree with previous theory.
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Huang, Rotstein, Fraden, Kasza, and Flynn study an aqueous solution of rod-shaped particles to look for transitions between isotropic, nematic, liquid, and gel states. The transitions are a function of particle concentration, temperature, and salt concentration in the water. For this experiment, Huang ''et al.'' create particles by coating bacteriofage fd with poly(N-isopropylacrylamide) (PNIPAM). The researchers use both rheological measurements and light scattering measurements as well as qualitative observations to characterize the properties of the solutions which do not agree with previous theory.
  
The bacteriofage fd (a polymer with negative surface charge) is itself approximately rod-shaped. The researchers coat the bacteriofage fd with the polymer PNIPAN to give the particle-particle interactions a temperature dependence. The temperature dependence of solubility of PNIPAM and bacteriofage fd are different. The researchers also varied the ion content of the water to change the particle-particle interactions.
+
The bacteriofage fd (a polymer with negative surface charge) is itself approximately rod-shaped. The researchers coat the bacteriofage fd with the polymer PNIPAM to give the particle-particle interactions a temperature dependence. The water solubility of PNIPAM is strongly temperature dependent. Below 32 degrees C, the polymer is soluable, while above 32 degrees C, the polymer becomes hydrophobic. Thus, at low temperatures, the polymer extends from the bacteriofage fd into the water, while at high temperatures, the polymer forms tight coils. When the polymers are extended, one observes steric stabilization, while ionic forces dominate when the polymers shrink into small balls. The researchers also varied the ion content of the water to change the particle-particle interactions.
  
Theory predicts that low particle concentrations yield isotropic solutions, high concentrations yield nematic solutions, and intermediate concentrations yield a mixed istropic-nematic phase. Theory also predicts that as temperature increases, the temperature range of this istropic-nematic widens (see figure 1).
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Theory predicts that low particle concentrations yield isotropic solutions, high concentrations yield nematic solutions, and intermediate concentrations yield a mixed isotropic-nematic phase. Theory also predicts that as temperature increases, the temperature range of this istropic-nematic widens (see figure 1). Huang ''et. al.'' do not observe the widening of the isotropic-nematic temperature range. Rather, the solutions formed gels at temperatures below the expected widening temperature.
 
+
Debye Length
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[[image: Figure2RodLike.png |400px|thumb|left|Figure 1. A phase diagram of both theory and experiments. Figure 2 from [1] ]]
 
[[image: Figure2RodLike.png |400px|thumb|left|Figure 1. A phase diagram of both theory and experiments. Figure 2 from [1] ]]
  
 
The researchers compared two samples: a) a low concentration of rod-like particles (9.6 mg/ml) which is isotropic, and b) a higher concentration of rod-like particles (21 mg/ml) which has nematic structure. Both solutions have an ionic strength of 144mM.
 
The researchers compared two samples: a) a low concentration of rod-like particles (9.6 mg/ml) which is isotropic, and b) a higher concentration of rod-like particles (21 mg/ml) which has nematic structure. Both solutions have an ionic strength of 144mM.
 
-salt and temperature varied -20 degrees to 200 degrees C
 
-debye length
 
-sol-gel transition
 
-comparison to predictions
 
  
 
== Soft Matter Details ==
 
== Soft Matter Details ==

Revision as of 17:18, 4 November 2009

Overview

  • [1] Huang, F., Rotstein, R., Fraden, S., Kasza, K., & Flynn, N. Soft Matter. 5, 2766-2771 (2009).
  • Keywords: Isotropic, Nematic, Viscoelastic, Sol-Gel Transition, Colloidal Rods, Phase Transition

Summary

Huang, Rotstein, Fraden, Kasza, and Flynn study an aqueous solution of rod-shaped particles to look for transitions between isotropic, nematic, liquid, and gel states. The transitions are a function of particle concentration, temperature, and salt concentration in the water. For this experiment, Huang et al. create particles by coating bacteriofage fd with poly(N-isopropylacrylamide) (PNIPAM). The researchers use both rheological measurements and light scattering measurements as well as qualitative observations to characterize the properties of the solutions which do not agree with previous theory.

The bacteriofage fd (a polymer with negative surface charge) is itself approximately rod-shaped. The researchers coat the bacteriofage fd with the polymer PNIPAM to give the particle-particle interactions a temperature dependence. The water solubility of PNIPAM is strongly temperature dependent. Below 32 degrees C, the polymer is soluable, while above 32 degrees C, the polymer becomes hydrophobic. Thus, at low temperatures, the polymer extends from the bacteriofage fd into the water, while at high temperatures, the polymer forms tight coils. When the polymers are extended, one observes steric stabilization, while ionic forces dominate when the polymers shrink into small balls. The researchers also varied the ion content of the water to change the particle-particle interactions.

Theory predicts that low particle concentrations yield isotropic solutions, high concentrations yield nematic solutions, and intermediate concentrations yield a mixed isotropic-nematic phase. Theory also predicts that as temperature increases, the temperature range of this istropic-nematic widens (see figure 1). Huang et. al. do not observe the widening of the isotropic-nematic temperature range. Rather, the solutions formed gels at temperatures below the expected widening temperature.

Figure 1. A phase diagram of both theory and experiments. Figure 2 from [1]

The researchers compared two samples: a) a low concentration of rod-like particles (9.6 mg/ml) which is isotropic, and b) a higher concentration of rod-like particles (21 mg/ml) which has nematic structure. Both solutions have an ionic strength of 144mM.

Soft Matter Details

Experimental Methods:

Dynamic Light Scattering

Rheology

Phase Behavior:

Open Questions/Ongoing Research: