Polymer Chain Collapse in Supercritical Fluids. 2. Experimental Evidence

Abstract

Summary:The phase behavior of a polymer in a supercritical solvent at the LCST equilibrium limits is described in this work, in the proximity of u point, proposing the use of a conformational parameter, C. The results obtained by molecular simulation in an NVT ensemble have been correlated by extensive, varied experimental information. The relationship between polymer/solvent solubility parameters has shown that the behavior of these systems is a function of the energetic structure-interaction relationship between the polymer chain and the solvent. C results in a generalized parameter indicative of the phase stability of the solution. At greater magnitudes, the solution becomes unstable, requiring elevated pressure to stabilize. However, stable solutions are found at lower pressures when C approaches 1. The experimental evidence, together with the determination of the solubility parameter with the Sanchez-Lacombe equation (also obtained from the literature) strengthens this observation. The analysis of the polar contribution on the Hansen Parameter (HSP) enables their effect to be studied in systems where high polar interactions between the polymer and solvent (as in the case of biopolymers) are expected.