PRESSURE AND TEMPERATURE-DEPENDENCE OF THE VISCOSITY OF POLYMER-SOLUTIONS IN THE REGION OF PHASE-SEPARATION

For the system trans-decahydronaphthalene/polystyrene (M = 110000) and the ranges of pressure, temperature, composition, and shear rate under investigation (1-1000 bar, 10-16 °C, 8-15 wt % polymer, and 20-320 s-1), the viscosity coefficients ƞ increase in a fairly exact exponential manner by roughly a factor of 6 per 1000 bar. Special attention was paid to the demixing conditions which manifest themselves in a sharp discontinuity of the In ƞ vs. p curves. The comparison of the obtained demixing data with the previously measured critical lines demonstrates that at elevated pressures the polymer solutions are stabilized by stirring, i.e., they demix at higher pressure (300 bar) or lower temperature (2 K). A molecular mechanism for this finding involving molecular interactions is put forward. For homogeneous solutions ƞ increases exponentially with concentration. The interpretation of ƞ(p, T) with respect to the apparent volumes of activation, Vǂ, and the energies of activation, Eǂ, shows the following: (i) The hypothesis that the pressure dependence of is essentially given by the pressure dependence of Eǂdoes not hold true for the present case and (ii) maximum in Vǂis found at the critical composition by analogy with the well-known maximum in Eǂ; the increase in Vǂ, associated with an approach of the critical point, is however much less pronounced than that of Eǂ. © 1979, American Chemical Society. All rights reserved.