FLOW-STRUCTURE RELATIONSHIP OF SHEAR-THICKENING SURFACTANT SOLUTIONS

The shear-thickening transition in dilute surfactant solutions is inve stigated using rheology and small-angle neutron scattering. Steady she ar experiments on a new thickening system, the tosylate of cethyltrime thylammonium, revealed a continuous increase of the apparent viscosity above a critical strain fate (gamma)over dot(c). Concentration and te mperature variations of (gamma) over dot(c) are derived, and the forme r is found to be in contradiction with a theoretically predicted gelat ion. From the scattering under shear, we establish a clear correlation between flow and structure. In the thickening region, the patterns ar e due to the superposition of two coexisting states, one viscoelastic entangled sheared network and one still purely viscous made of short a ggregates. At higher (gamma) over dot(c), the former state dominates a nd its increasing orientation results in shear-thinning.