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Thermal and Mass Diffusion in a Semidilute Good Solvent-Polymer Solution



K J. Zhang, M E. Briggs, R W. Gammon, J V. Sengers, Jack F. Douglas


The Soret coefficient ST and collective (mass) diffusion coefficient Dc of polystyrene dissolved in the good solvent toluene is measured over a range of concentrations and molecular weights using an optical beam deflection method. Our measurements indicate that ST scales inversely with the polymer translational diffusion coefficient in dilution solutions and exhibits a power law scaling with polymer concentration and an independence of polymer molecular weight in semi-dilute solutions. These findings are consistent with the known scaling of 1/Dc in dilute and semi-dilute polymer solutions, the relative insensitivity of the thermal diffusion coefficient DTh of polystyrene in toluene to polymer concentration, and the relation ST = DTh/Dc from irreversible thermodynamics. We were able to represent our ST and Dc data by theoretically motivated reduced concentration master curves, but the concentration-molecular weight scaling variable were found to be different for each transport property -- a result contrary to theoretical expectations. However, the asymptotic concentration scaling exponents deduced from these data fits are compatible with DeGennes' scaling arguments for Dc and with modern estimates at the chain size exponent Ņ for swollen polymers in a good solvent.
Journal of Chemical Physics
No. 5


collective diffusion coefficient, polymer solutions, Soret coefficient, temperature gradient, thermal diffusion coefficient


Zhang, K. , Briggs, M. , Gammon, R. , Sengers, J. and Douglas, J. (1999), Thermal and Mass Diffusion in a Semidilute Good Solvent-Polymer Solution, Journal of Chemical Physics, [online], (Accessed April 22, 2024)
Created July 31, 1999, Updated October 12, 2021