| Abstract
| - Self-diffusion mechanisms of a surfactant molecule in entangledthreadlike micelles formed from amixture of cetyltrimethylammonium bromide (CTAB) and sodium salicylate(NaSal) in aqueous solution(CTAB:NaSal/W) are discussed. The self-diffusion coefficient(Dself) for the cetyltrimethylammonium(CTA+)cation in the micelle was calculated on the basis of a phantom networkmodel. Two formulations for theself-diffusion coefficient are derived for two separate regimes withrespect to time and space. When therelaxation time (τm) for the micellar system is short,Dself is represented as〈ξ2〉{6τmP(Le,τm)},where 〈ξ2〉is the mean square of the entanglement spacing which depends on theCTA+ concentration andP(Le,τm)is a probability for the CTA+ cation to remain in theinitial part of the threadlike micelle with the averagecontour length of Le between two entanglements.On the other hand, when τm is long,Dself is expressedas(2Q/3)(Dlat/2τm)1/2,where Q and Dlat are the persistencelength of the threadlike micelle and the lateraldiffusion coefficient of the CTA+ cation along themicellar contour, respectively. Dselfvalues and activationenergies determined experimentally by use of a forced Rayleighscattering technique agree with thosecalculated based on the model.
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