科研之友
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摘要
Phase control is now challenging the manufacturing of electroactive polyvinylidene fluoride (PVDF) toward energy storage applications. Currently, the state-of-the-art approach in fabricating virgin, unfilled PVDF with predominantly the beta-phase always needs complex procedures and requires extreme processing conditions. Herein, for the first time, we fabricated PVDF with a controlled beta-phase under mild processing conditions by introducing a cyclic pulsating pressure (CPP) during hot pressing. Fourier-transform infrared spectroscopy and wide-angle X-ray diffraction revealed the relationship between the beta-phase fraction and CPP condition. Consequently, we obtained melt-processed, virgin, and unfilled PVDF with 72.2% beta-phase, as well as enhanced dielectric and mechanical properties, under hot pressing with a maximum pressure as low as 40 MPa. The mechanism of volume reduction-induced beta-phase formation was proposed and verified. Moreover, in contrast to the conventional understanding of the phase transition that requires continuous ultrahigh pressure, we find that the inclusion of the relaxation process can further promote the formation of the beta-phase. We believe that this work breaks existing knowledge of phase transition behavior of PVDF and further paves an avenue toward manufacturing PVDF with a controlled phase structure under simple, highly efficient, and mild processing conditions.
