Macroporous PVDF/TiO2 membranes with three-dimensionally interconnected pore structures produced by directional melt crystallization

• PVDF/TiO2 membranes were fabricated by a novel melt crystallization method.
• Directionally grown solvent crystals acted as a 3D interconnected pore forming agent.
• Outstanding pure water flux and protein adsorption resistance were achieved.

Techniques to fabricate polymer membranes with improved performance have been actively developed over the past several decades. Most conventional manufacturing processes are based on amorphous phase separation, which often restricts the formation of interconnected pores, resulting in high tortuosity. Herein, we demonstrate the fabrication of polyvinylidene fluoride (PVDF)/TiO2 composite membranes with highly interconnected pore structures. Vertically oriented pores could be produced by continuous growth of solvent crystals under a controlled temperature gradient and then removing solvent crystals via freeze drying. Crystal nucleation and growth could offer better control of pore morphology, size, and connectivity. The incorporation of TiO2 into PVDF membranes not only improved the hydrophilicity, but also enhanced protein resistance of the membrane. The pure water flux of PVDF/TiO2 composite membranes with interconnected porosity was excellent, six times higher than that of commercial PVDF membranes having similar pore size. This novel preparation method could expand the variety of structures and properties of such membranes and hence their areas of application.

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