Molecular flexibility effects upon liquid dynamics

J. V. Heffernan, J. Budzien, A. T. Wilson, R. J. Baca, V. J. Aston, F. Avila, J. D. Mccoy, D. B. Adolf, J Chemical Physics, 126, 184904 (2007).

Simulation results for the diffusive behavior of polymer chain/penetrant systems are analyzed. The attractive range and flexibility of simple chain molecules were varied in order to gauge the effect on dynamics. In all cases, the dimensionless diffusion coefficient, D*, is found to be a smooth, single-valued function of the packing fraction, U+03B7. The functions D*(U+03B7) are found to be power laws with exponents that are sensitive to both chain stiffness and particle type. For a specific system type, the D*'s for both penetrant and chain-center-of-mass extrapolate to zero at the same packing fraction, U+03B70. This limiting packing fraction is interpreted to be the location of the glass transition, and (U+03B70-U+03B7), the distance to the glass transition.

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