Europhys. Lett.
Volume 66, Number 1, April 2004
Page(s) 132 - 138
Section Interdisciplinary physics and related areas of science and technology
Published online 01 April 2004
Europhys. Lett., 66 (1) , pp. 132-138 (2004)
DOI: 10.1209/epl/i2003-10189-8

Shear-induced constraint to amphiphile chain dynamics in wormlike micelles

W. M. Holmes, M. R. López-González and P. T. Callaghan

MacDiarmid Institute for Advanced Materials and Nanotechnology School of Chemical and Physical Sciences, Victoria University of Wellington P.O. Box 600 Wellington, New Zealand

(Received 15 August 2003; accepted in final form 26 January 2004)

The influence of shear on the proton NMR spectrum of the wormlike micellar system 10% w/v cetylpyridinium chloride/sodium salicylate in $\chem{{}^2H_2O}$ brine is investigated as a function of time, shear rate and radial position in the gap of a cylindrical Couette cell. The protons of the surfactant chains show a spectral effect which correlates with the rheological response. In particular we observe a clear subdivision of the cetyl chain dynamics into both motionally constrained and freely reorientating fractions. With shear, the surfactant chains exhibit increased motional constraint, with the chain response rate mirroring the stress response. We attribute this effect to either micellar alignment or an increase in the micelle persistence length.

83.10.-y - Rheology: Fundamentals and theoretical.
83.50.Ax - Steady shear flows, viscometric flow.
68.18.Jk - Phase transitions.

© EDP Sciences 2004