A Review on Polymeric Membranes and Hydrogels Prepared by Vapor-Induced Phase Separation Process

In 1918, Zsigmondy and Bachmann presented a new method to induce phase separation of a homogeneous polymeric solution from a vapor phase. The so-called vapor-induced phase separation (VIPS) was born. In a century, the body of knowledge on polymer membranes and hydrogels prepared by VIPS has grown importantly, which suggests the need for a critical review. Slowness of mass transfers involved in VIPS, attributed to the resistance at the gaseous phase/liquid phase interface, permits reaching better control of polymer membrane formation than with the popular wet-immersion process. As a result, a broad variety of morphologies can be obtained and well controlled. The control of testing conditions and formulation parameters also permits tuning and tailoring morphologies, which arises in various membranes properties, and led scientists to investigate the possibility of forecasting mass transfers in VIPS. Therefore, at the end of the twentieth century, first models were developed to describe this process, and validated by comparing simulated data to experimental results. Afterwards, studies demonstrated the possibility of predicting membrane morphologies from the knowledge of operating conditions. This article aims at reviewing the work done so far reporting this process to prepare polymer membranes and hydrogels. The experimental set-ups will be introduced as well as the different polymer/solvent/nonsolvent and polymer/additive(s)/solvent/nonsolvent systems used and the morphologies obtained. The effect of testing conditions and formulation parameters on the structure of the matrices will be subsequently discussed. Close attention will be given to the fundamental theory of VIPS before moving onto the potential applications of such polymer matrices.