Title:	Effect of screening of intermicellar interactions on the linear and nonlinear rheology of a viscoelastic gel
Authors:	Bandyopadhyay, Ranjini Sood, A.K.
Issue Date:	2003
Publisher:	American Chemical Society
Citation:	Langmuir, 2003, Vol.19, p3121-3127
Abstract:	We report our studies of the linear and nonlinear rheology of aqueous solutions of the surfactant cetyl trimethylammonium tosylate (CTAT) with varying amounts of sodium chloride (NaCl). The CTAT concentration is fixed at 42mM and the salt concentration is varied between 0mM to 120mM. On increasing the salt (NaCl) concentration, we see three distinct regimes in the zero-shear viscosity and the high frequency plateau modulus data. In regime I, the zero-shear viscosity shows a weak increase with salt concentration due to enhanced micellar growth. The decrease in the zero-shear viscosities with salt concentration in regimes I I and III can be explained in terms of inter-micellar branching. The most intriguing feature of our data however, is the anomalous behavior of the high frequency plateau modulus in regime II (0.12 $\le \frac{[NaCl]}{[CTAT]} \le$ 1. 42). In this regime, the plateau modulus {\it increases} with an increase in NaCl concentration. This is highly counter-intuitive, since the correlation length of concentration fluctuations and hence the plateau modulus $G_{\circ}$ are not expected to change appreciably in the semi-dilute regime. We propose to explain the changes in regime II in terms of the unbinding of the organic counterions (tosylate) from the CTA$^{+}$ surfaces on the addition of NaCl. In the nonlinear flow curves of the samples with high salt content, significant deviations from the predictions of the Giesekus model for entangled micelles are observed.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/4653
ISSN:	0743-7463 1520-5827 (Online)
Alternative Location:	http://arxiv.org/abs/cond-mat/0012473
Copyright:	2003 American Chemical Society
Appears in Collections:	Research Papers (SCM)

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