Fabrication and characterization of PVDF membranes via an in situ free radical polymerization method

• In situ free radical polymerization avoids further surface modifications of PVDF membranes.
• In situ polymerization is beneficial to improve the micro-structure adjustment of PVDF solutions.
• In situ polymerization results in the tuned configurations of PVDF membranes bulk.

In situ free radical polymerization was proven to be successful for the preparation of PVDF membranes with superior mechanical behaviors and enhanced antifouling properties. Micro-structure adjustment of PVDF solution via in situ polymerization was investigated by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The DLS and SEM results verified the formation of supramolecular polymer–copolymer aggregates. The narrow distribution of the supramolecular aggregates explained the decreasing surface tension, increasing viscosity with trivial strain thinning behavior and accelerating precipitation rate of the PVDF casting solution. The resultant PVDF membranes possessed narrowly distributed pore size and molecular weight cut off (MWCO) of the final filtration properties, which were attributed to the aggregates; additionally, their corresponding mean effective pore size (μ) and MWCO increased with increasing concentration of the monomers via in situ polymerization. Further, in situ polymerization not only enlarged the recovery water flux after filtration experiments with bovine serum albumin (BSA) but also improved the hydrophilicity of both the top-surface and the bottom-surface of the PVDF membranes. Additionally, in situ polymerization modulated the PVDF membrane configurations, varying from stripe-shaped grains to agglomerates of globule (with one of the globules bearing on the surface of another). The tunable morphologies, combined with the progressive enhanced crystallinity of the α and β phase (largely in the β phase form), were used to interpret the superior mechanical properties of the resulting PVDF membranes.