Dependency of polyacrylonitrile membrane structures on Hansen solubility parameters during non-solvent induced phase separation

In this study, non-solvent induced phase separation (NIPS) is used to prepare polyacrylonitrile (PAN) based membranes. A thorough analysis on the correlations between coagulation conditions and membrane structures was carried out according to Hansen solubility parameters of coagulants and solvents. When coagulant is various, a larger Hansen solubility distance (R-a) between PAN and coagulant leads to a quicker phase separation and faster growth of finger-like pores. By comparison, when PAN solvent is tuned by adding small amount of water, the R-a plays totally different roles for the formation of dense layer and the growth of finger-like pores. The structural variations of PAN membranes have been mapped in Hansen space according to the R-a. Additionally, the low temperature induced sol-gel transition of PAN solution also affects the pore structures of the resultant membranes. These results would be helpful for better understanding the NIPS and fabricating PAN and other types of polymer membranes with desired structures and performances.