Dynamics of evaporation in polymer/solvent films - importance in asymmetric polymeric membrane formation

Synthetic membrane technology has shown a considerable growth over the past 25 years in a wide-variety of applications. Approximately 60% of synthetic polymeric membranes are currently utilized as semipermeable barrier layers in the separations industry. Synthetic membranes are an attractive alternative for conventional separation processes since they avoid the energy intensive phase transition inherent in many of these processes. The research described is directed toward obtaining a fundamental understanding of the transport processes that take place during the evaporation step and the manner in which they may influence the membrane morphology and selective permeation properties. The primary objective is to resolve the long-standing debate regarding the value of the evaporation step. Such results will aid efforts to formulate new and improved membranes with enhanced quality control. The authors report the development of a comprehensive model for solvent evaporation from a forming polymer film (i.e., evaporative casting process) which incorporates the significant surface cooling effects ignored in prior analyses and the experimental validation of the model.