Introduction

Misibility or phase separation in polymer solutions may be induced ( i) by a change in temperature, or (ii) by a change in composition as result of adding a third component such as a solvent or a non-solvent to a system, or as a result of progress of a reaction, or (iv) due to a change in pressure.1-4 These are schematically represented in Figure 1. Even though not shown in the figure, applied fields such as shear may also induce phase separation. Of these, the temperature- and solvent-induced phase separation are the most common methodologies that are used in membrane formation and other processes that lead to porous materials. Reaction induced phase separation is encountered in polymerization, and in particular in systems that undergo crosslinking where a homogeneous system may enter the two-phase region with an increase in degree of polymerization (DP) or conversion. Pressure-induced phase separation (PIPS) is essentially an unavoidable integral step in all processes that employ near-critical or supercritical fluids. This is because at some point in the process the pressure

0 0

Post a comment