Facile way of dynamically tailoring microporous structures in polyvinylidene fluoride films prepared by thermally induced phase separation

Polyvinylidene fluoride (PVDF) films were prepared via thermally induced phase separation (TIPS) using diphenyl carbonate as the diluter in an attempt to disclose the competitive relationship between crystal growth and droplet growth during phase separation process. By varying the quenching temperature different temperature gradient fields were established, which were theoretically evaluated via enthalpy transformation method. The effects of polymer concentration and quenching temperature on evolution of hierarchical morphologies in TIPS films were systematically investigated. According to the morphological characteristics, the cross-sectional morphology of the films with lower polymer concentration ( Φ P = 25%) could be divided into three layers; while that of higher polymer concentration counterpart ( Φ P = 55%) only presented a bi-layered structure. The reason for this could be ascribed to the effect of cooling rate on both crystal growth and droplet growth during TIPS process, which further determined the formation of the hierarchical structure in microporous films. With an increasing quenching temperature, both pore size and porosity of PVDF films increased, accompanied by an improvement on both thermal stability and dynamic mechanical thermal property. The present study could insightfully supply a facile route to fabricate structure-controllable microporous films of crystalline polymers via an appropriate regulation of the TIPS quenching parameters. Graphical Based upon the phase diagram of polyvinylidene fluoride (PVDF)/diphenyl carbonate (DPC) system, the effects of polymer concentration and quenching temperature on the morphologies in thermally induced phase separation (TIPS) films are quantitatively established. TIPS films with lower (below monotectic point) and higher (above monotectic point) polymer concentrations present three-layered and bi-layered hierarchical structures, respectively, primarily originating from the competition between crystal growth and droplet growth during the phase separation.