Fundamentals of nonsolvent-induced phase separation

Presented in this chapter are the fundamental principles of solution thermodynamics and process kinetics for preparation of nonsolvent-induced phase separation membranes. The principles help to explain the origin of structure asymmetry and the formation of separation layers and provide guidelines to identify the important factors involved in membrane formation and to rationalize the complicated interplay of the factors. Special attention is paid to the effects of the competition between different demixing mechanisms and the evolution of phase-separated domains on controlling membrane morphology and tailoring membrane separation performance, with stressing on the role of polymer solution gelation and how it can influence the mass transport kinetics, the solution thermodynamic instability, and the growth of phase-separated domains. The principles are then extended to clarify the roles of modification additives in membrane formation and the application of using additives to modify the structure and performance of hollow fiber membranes is also discussed.