Concurrently enhanced mechanical properties and capacitive performance in all-organic dielectric polymer blend via phase separation

Abstract

Phase separation of polymer blends has attracted much interest in designing high-performance materials with specific mechanical and dielectric properties. To this end, three types of poly(methacrylic ester)s, including poly(methyl methacrylate) (PMMA), poly(butyl methacrylate) (PBMA), and poly(isobutyl methacrylate) [P(iBMA)], have been incorporated in the poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] matrix, respectively. As exemplified in P(VDF-HFP)/P(iBMA) blended films, a conspicuous phase separation is experimentally observed and the blended film presents an enhanced Young's modulus and a one-fold increment in the elongation over the pristine P(VDF-HFP). The excellent plasticity is benefited from the interfacial regions between the two phases, which could effectively pin the cracks and retard the slippage under deformation. Simultaneously, an ultra-high Weibull breakdown strength (∼774 MV/m) is obtained in the blends, benefiting from the improved Young's modulus and excellent plasticity. The blends are endowed with an excellent energy storage density (∼21 J/cm3 at 830 MV/m), along with an impressive cycling stability. In contrary, P(VDF-HFP)/PMMA and P(VDF-HFP)/PBMA blended films sacrifice the plasticity due to the scarcity of phase separation; therefore, even though Young's moduli have been improved, there is no remarkable improvement for breakdown strengths and energy storage performances. The experimental results are augmented by molecular dynamics simulations. This contribution provides a facile approach to develop high-performance polymer dielectric materials through a phase separation design and emphasize the importance of plasticity for breakdown strength.