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RESEARCH PRODUCT

A friction factor analysis of the coupling between polymer/solvent self- and mutual-diffusion: polystyrene/toluene

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The Bearman statistical mechanical theory, which couples the mutual-diffusion and self-diffusion coefficients via friction factors, has been applied to polystyrene/toluene solutions with polystyrene molecular weights of 18 kDa and 900 kDa. Toluene and polystyrene self-diffusion coefficients, obtained from the literature and measured here, along with polystyrene/toluene binary mutual-diffusion coefficients and thermodynamic data, were employed to independently calculate the three friction coefficients (ξ 12 , ξ 11 , and ξ 22 ) required to describe transport within binary solutions. Results reveal that the frequently used geometric mean approximation (GMA) for relating the friction coefficients consistently underestimates ξ 22 and worsens with increasing polymer molecular weight. The GMA is found to be appreciably more accurate than the arithmetic mean approximation. A formalism recently proposed by Vrentas et al. has also been evaluated for this system and is found to describe the concentration dependence of ξ 11 very well. The Vrentas model, therefore, can accurately predict mutual-diffusion coefficients from solvent self-diffusion coefficients for polystyrene/toluene solutions.