Self-diffusion of Micelles and Viscoelasticity of Aqueous Detergent Solutions

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Abstract
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 CDGN, 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 CDCD and when CDCD. 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.

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