SynopsisA novel method of investigating the link between molecular features of polymer molecules and the rheological properties of dilute polymer solutions has been investigated. It applies the dissipative particle dynamics (DPD) computer simulation technique, which introduces a lattice-gas automata time-stepping procedure into a molecular-dynamics scheme, to model bead-and-spring-type representations of polymer chains. Investigations of static and dynamic scaling relationships show that the scaling of radius of gyration and relaxation time with the number of beads are consistent with the predictions of the Rouse-Zimm model. Both hydrodynamic interaction and excluded volume emerge naturally from the DPD polymer model, indicating that a realistic description of the dynamics of a dilute polymer solution can be obtained within this framework, and that very efficient computer simulations are possible. 0 1995 Society of Rheology.

We report gas solubilities in molten polymers for two systems: the solubility of carbon dioxide in poly(dimethylsiloxane) and the solubility of 1,1-difluoroethane in polystyrene are measured in the range of temperatures and pressures where the gas is supercritical. The solubility data are correlated by two lattice-theory-based equations of state, namely, the Sanchez-Lacombe and Panayiotou-Vera equations of state, which employ a single adjustable binary interaction parameter. Both equations of state provide satisfactory descriptions of the solubility data when the binary interaction parameter is allowed to depend on temperature. The utility of the mixture equations of state is illustrated by predictions of swollen volume, isothermal compressibility, and thermal expansion coefficient for the mixtures over the range of data.

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The dynamics of a bead-and-spring polymer chain suspended in a sea of solvent particles are examined by dissipative particle dynamics (DPDJ simulations. The solvent is treated as a structured medium, comprised of particles subject to both solvent-solvent and solvent-polymer interactions and to stochastic Brownian forces. Thus hydrodynamic interactions among the beads of the polymer evolve naturally from the dynamics of the solvent particles. DPD simulations are about two orders of magnitude faster than comparable molecular dynamics simulations. Here we report the results of an investigation into the effects of confining the dissolved polymer chain between two closely spaced parallel walls. Confinement changes the polymer configuration statistics and produces markedly different relaxation times for chain motion parallel and perpendicular to the surface. This effect may be partly responsible for the gap width-dependent rheological properties observed in nanoscale rheometry.