Porous poly(vinylidene fluoride) (PVDF) membranes were prepared by immersion precipitation method from ethanol/DMSO/PVDF and water/DMSO/PVDF systems. The polymorphism of the formed membranes was studied by changing the PVDF concentration in dope solutions and precipitation temperature. For all the obtained membranes, differential scanning calorimetry (DSC) thermograms showed a similar melting peak temperature, wide angle X-ray diffraction (WAXD) analysis indicated that PVDF crystallized into á form crystalline structure, while different results from Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) implied that membrane surfaces consisted of a mixture of alternating trans and gauche chains in á phase crystalline domains and all-trans planar zigzag chains in â phase. The membranes precipitated from water/DMSO/PVDF system demonstrated lower total crystallinity but higher â/á phase ratio at membrane surface than those from ethanol/DMSO/PVDF system. When water at 30 °C was used as nonsolvent, the â/á phase ratio increased with the increase in PVDF content in the dope. However, the trend reversed when water at 60 °C or ethanol was used instead. These findings suggest that the formation of crystalline phases in PVDF membranes relies on more kinetic and thermodynamical factors than mass transfer between solvent–nonsolvent. The water contact angle analysis, water absorbance ratio measurement, and BSA static adsorption experiments results of the dense membranes with various crystalline structures reveal the improved hydrophilicity, wettability, and protein-resistance characteristics of the surfaces with higher â phase content.

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