Pressure-Induced Phase Separation in Polymer Solutions: Kinetics of Phase Separation and Crossover from Nucleation and Growth to Spinodal Decomposition in Solutions of Polyethylene in n-Pentane

Abstract

The kinetics of pressure-induced phase separation (PIPS) in solutions of polyethylene (Mw = 108 000, PDI = 1.32) in n-pentane has been studied using time- and angle-resolved light scattering. Controlled pressure quench experiments were conducted at different polymer concentrations (0.49, 0.97, 2.07, 2.8, 4.1, 5.0, and 10.8% by mass) to determine both the binodal and spinodal envelopes and the critical polymer concentration. At each concentration, a series of rapid pressure quenches with different depths of penetration into the region of immiscibility were imposed, and the time evolutions of the scattered light intensities were followed to determine the pressure below which the mechanism changes from “nucleation and growth” to “spinodal decomposition”. The crossover is identified from the characteristic fingerprint scattering patterns associated with each mechanism. The spinodal decomposition process is characterized by the formation and evolution of a spinodal ring during phase separation that leads to a ...