Study on the membrane formation mechanism of PVDF/PVDF-CTFE blends

Background: The low hydrophobicity and weak alkali resistance of PVDF limit its application in the field of hydrophobic membranes, so membrane modification is necessary. Blending is one of the common modification methods, and membrane preparation and modification are completed simultaneously. Exploring suitable blending system and studying its membrane formation mechanism is the key to obtain excellent hydrophobic membranes. Methods: XPS and EDX techniques were used to detect the content of PVDF-CTFE on the membrane surfaceinterfaces to explore the formation mechanism of blend membranes. And it was further explained by the changes of membrane properties such as water contact angle, alkali resistance, mechanical strength, etc. Significant findings: We believe that there was a unique competitive precipitation mechanism for the mixed system of PVDF-CTFE and PVDF in the process of membrane formation via the NIPS method. The PVDF-CTFE will preferentially precipitate to form the membrane surface-interfaces (blend membrane surface and pore wall). While the PVDF subsequently precipitates to form the sponge-like structure, constituting the membrane body. This may further improve the basic theory of blend membrane preparation and is expected to be extended to the investigation of other mixed systems.