Formation of nanosheets-assembled porous polymer microspheres via the combination effect of polymer crystallization and vapor-induced phase separation

A facile and versatile route is demonstrated to fabricate nanosheets-assembled porous polymer microspheres via the ingenious combination of polymer crystallization promoted by high temperature and vapor-induced phase separation (VIPS). Water vapor which permeates into the polymer solution promotes the precipitation of hydrophobic polyacrylonitrile (PAN). High temperature promotes PAN crystallization and assembling into hierarchical porous microspheres (about 1–3 μm). Interestingly, the addition of polyethyleneimine (PEI) functioning as nucleation sites and steric stabilizer can also promote PAN crystallization owing to their strong interactions. In this protocol, polymer composition , preparation temperature, solvent type and solution concentration are critical to determine the final morphologies of porous microspheres. This versatile strategy for fabricating nanosheets-assembled porous microspheres can be extended to other semi-crystalline/crystalline polymers, which could hopefully be applied in drug delivery, energy storage, separation,and purification, etc.