A MODIFIED HOLE THEORY OF POLYMERIC FLUIDS .2. MISCIBILITY BEHAVIOR AND PRESSURE-DEPENDENCE OF THE SYSTEM POLYSTYRENE CYCLOHEXANE

Experimental miscibility behavior and the influence of pressure upon it are discussed with the modified hole theory introduced in the previous paper. For the first time the complicated pressure dependence for the system polystyrene/cyclohexane is theoretically reproduced. The modified hole theory and Simha-Somcynsky hole theory are compared. Thermodynamically the pressure dependence of the critical temperature is related to the compositional curvature of the volume of mixing. According to the modified hole theory a complicated composition dependence for the volume of mixing is predicted as a result of a delicate interplay of two volume effects. Spanning the complete composition range a volume contraction is predicted directly related to the change in the structure parameter defined in the hole theory. However, this overall contraction is perturbed by a volume expansion related to the packing efficiency of different component segments. These two distinct volume contributions result in a complicated dependence of the volume of mixing on composition and set the hole theories apart from other equation-of-state theories currently available. © 1990, American Chemical Society. All rights reserved.