Nano-porous shape memory membrane: Fabrication based on double bicontinuous structures in ternary blend and pore-size manipulation by macroscopic deformation

Nano-pore size is the key factor to determine the performance of porous membrane in various applications. The programmable and continuous manipulation of it remains as a great challenge. In this work, nano-porous shape memory polymer (SMP) membrane has been fabricated successfully in ternary blend of PVDF, PBSU and random copolymer (BMG) based on the special interface interaction and complicated phase behaviors among them. On one hand, phase separation takes place, producing bicontinuous structures with the characteristic size of microns including BMG rich phase and PVDF/PBSU mixed phase. The former provides shape memory effect in which cross-linked points and network play the roles of shape fixed phase and recovery phase respectively; on the other hand, exclusion of PBSU during crystallization of PVDF contributes to bicontinuous structures in nanoscale. The removal of PBSU based on double bicontinuous structures results in the interconnected nano-pores. The obtained nano-porous PVDF/BMG composite membranes possess not only shape memory performance, but also the interpenetrated channels. The pore size has been manipulated successfully by means of biaxial tension based on the proportional deformation in macro-and micro-scales. Our results provide a new strategy for the fabrication of nano-porous SMPs and the manipulation of pore size in them.