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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A least-squares method for correlation function profile analysis using a histogram approximation is described. The method is completely general, especially for bimodal distributions, and compares favorably with the method of cumulants. The measured photoelectron time-correlation function yields a histogram of the linewidth distribution which can be related uniquely to the particle size. The analysis is tested using simulated data with unimodal and bimodal size distributions. In our verification of the method using aqueous suspensions of Dow latex spheres, we have shown that our method is not only consistent with the results from electron microscopy, but that it is more precise and truly measures the hydrodynamic size of particles suspended in fluids.

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Viscosity curves were measured for polydimethyl siloxane (PDMS) melts swollen with dissolved carbon dioxide at 50 and 80ЊC for shear rates ranging from 40 to 2300 s 01 , and for carbon dioxide contents ranging from 0 to 21 wt %. The measurements were performed with a capillary extrusion rheometer modified for sealed, highpressure operation to prevent degassing of the melt during extrusion. The concentration-dependent viscosity curves for these systems are self-similar in shape, exhibiting low-shear rate Newtonian plateau regions followed by shear-thinning ''power-law'' regions. Considerable reduction of viscosity is observed as the carbon dioxide content is increased. Classical viscoelastic scaling methods, employing a composition-dependent shift factor to scale both viscosity and shear rate, were used to reduce the viscosity data to a master curve at each temperature. The dependence of the shift factors on polymer chain density and free volume were investigated by comparing the shift factors for PDMS-CO 2 systems to those obtained by iso-free volume dilutions of high molecular weight PDMS. This comparison suggests that the free volume added to PDMS upon swelling with dissolved carbon dioxide is the predominant mechanism for viscosity reduction in those systems.

is used to predict viscoelastic scaling factors describing the effect of dissolved gas content on the viscosity curves of polystyrene melts swollen with dissolved carbon dioxide and dissolved 1,1difluoroethane. The predictions of the theory are compared to viscoelastic scaling factors measured by Kwag et al. 2 (J. Polym. Sci. B: Polym. Phys. 1999, 37, 2771 for each system at 150 and 175 °C, at concentrations up to 10 wt % of dissolved gas, and pressures ranging up to 22 MPa. The agreement between the theory and experiments is very good for the polystyrene-CO 2 system but only fair for the polystyrene-1,1-difluoroethane system. The experimental viscoelastic scaling factor values are also interpreted with the WLF equation to estimate the change in the underlying glass transition temperatures of the polystyrene-gas mixtures. The glass transition temperatures estimated from these rheological data are in very good agreement with values directly measured for polystyrene-CO 2 mixtures and with the theory of Condo et al. 3 (Macromolecules 1992, 25, 6119).

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