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 (ΦP = 25%) could be divided into three layers; while that of higher polymer concentration counterpart (ΦP = 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.
Thermoresponsive shape-memory polymers (TSMPs) are materials that can memorize temporary shapes and can restore to their permanent shapes upon stimulus. This ability is driven by reversible deformation (ε re ); however, the deformation of TSMPs inevitably involves unfavorable irreversible deformation (ε ir ). Consequently, avoiding the ε ir through macromolecular chemistry or/and physical blending has been the currently efficient methodology for designing or fabricating TSMPs. Herein, we report another methodology, programming cycle tests (PCT), which can select and remove unfavorable ε ir , thus taking the shape-memory performance to its limits. Moreover, PCT is a physical process that only involves a series of successive thermomechanical cycles. Therefore, this study provides a simple and efficient methodology for designing and fabricating TSMPs.
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