L. An and B. A. Wolf

"Combined Effects of Pressure and Shear on the Phase Separation of Polymer
Solutions"

*Macromolecules* **1998**, *31*, 4621-4625.

**Abstract:** Experimental information available in the literature on the
phase separation behavior of the system trans-decalin/polystyrene as a function
of pressure and shear rate ibr different molar masses M of the polymer was used
to check to which extent the effects of these two variables can be predicted
theoretically. The Sanchez-Lacombe theory served as a basis for the description
of the solutions at rest. To account for the nonequilibrium condition, the energy
stored by the sheared mixtures while flowing was added to the Gibbs energy of
mixing. The phase diagrams measured at rest and under atmospheric pressure can
well be described by one parameter (Delta epsilon*, measuring the interaction
energy between unlike mers); Delta epsilon* is found to vary linearly with M-0.5.
The pressure dependencies of the cloud points (constant M and constant composition)
are also modeled appropriately, if Delta epsilon* is allowed to decrease linearly
with rising pressure. The predictions concerning the influence of sheer are
only qualitatively correct: In accord with the experimental findings, the phase
separation conditions are practically identical for the stagnant and for the
flowing solutions at low pressures; the homogeneous region is, however, increasingly
extended by shear as pressure becomes larger.

preprint number: 183