Shear-induced constraint to amphiphile chain dynamics in wormlike micelles

Abstract

The influence of shear on the proton NMR spectrum of the wormlike micellar system 10% w/v cetylpyridinium chloride/sodium salicylate in 2H2O 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.