1991 Volume 19 Issue 1 Pages 45-49
The viscoelasticity and self-diffusion were investigated for aqueous solutions of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal). The concentration of CTAB, CD, was equal to that of NaSal, Cs. This system contains thread-like micelles and exhibits pronounced viscoelastic behavior. The storage modulus, G′, and loss modulus, G″, could be fitted with the Maxwell model of one relaxation time when CD<0.5M. The plateau modulus, GN, was proportional to CD2 over a wide range of CD. This property is similar to that of concentrated polymer solutions. The relaxation time, τ, was evaluated from the frequency at which G″ takes maximum. The self-diffusion coefficient, D, was measured by forced Rayleigh scattering measurement. The quantities D and τ-1 varied in a similar manner as a function of CD ; when CD<0.2M, they increased with CD and when CD<0.2M, they decreased with CD. This behavior is remarkably different from polymer solutions.The rate of diffusion may be controlled by the rate of the process where thread-like micelles cut across each other, a process proposed previously to describe the stress relaxation.
