ISSN:
1435-1536
Keywords:
Worm-like micelles
;
shear-induced phase separation
;
critical concentration
;
geminisurfactant
;
birefringence
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract We report a new type of structural transition induced by shear in dilute/semi-dilute giant micellar solutions in water. In equilibrium at rest, the micelles are randomly oriented and the viscosity varies between 10−3–10−2 Pa·s. Under shear, the solutions have no measurable anisotropy while the applied shear rate is inferior to a critical value as shown from the optical birefringence measurements and the electric conductivity measurements. The viscosity shows an abrupt increase beyond this critical shear rate, and the solution becomes strongly anisotropic. The Cryo-TEM pictures show aggregations of micelles in the sheared solution. Therefore, we conclude that a phase separation is induced by shear between surfactant rich and poor phases. The domain size of the surfactant rich phase seem to increase with shear. This transition was observed even for concentrations far below the overlap concentrationφ *. Furthermore, the characteristic times of the system, such as the rotational or translational diffusion time of micelles or the electrophoretic relaxation time are much smaller than the inverse of the critical shear rate (10−1 s). Thus, it is clear that shear alone is not enough to cause the phase transition. None of the existing theories seem to account for this shear-induced phase transition.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01188964
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