Investigation of Mass Transfer During Membrane Formation – a Route Leads to Insight of Membrane Morphology Control

Vapor induced phase separation, a membrane preparation method employing water vapor as coagulant to induce phase separation of a polymer solution to generate porous structure, has much different mass transport characteristics from the typical wet immersion process with water as coagulant. For such a process, not only the morphology of the prepared membranes is interesting, but also it is easier to investigate experimentally the mass transfer process associated with membrane formation. We will briefly introduce how FT-IR microscopy and confocal Raman spectroscopy Raman were used to study the mass transport characteristics of the contact of a polymer solution with humid air. With the knowledge of the composition change during membrane formation, in addition to the information of morphology evolution and the ternary phase diagram of polymer/solvent/water, we can get insight into the competition between mass transfer, phase separation, domain coarsening, and polymer crystallization during membrane formation. With the results several issues on membrane formation can be addressed, including the effect of mass transfer on phase separation mechanism, how to prepare membranes with inter-connected structure, and how to manipulate the micro and nano scale membrane structures.