Significantly Enhanced Dielectric Polarization and Breakdown Strength of Polyvinylidene Fluoride via Grafting with Sulfobetaine Methacrylate

Polymer capacitors have garnered extensive attention in modern electronic and power systems. Nonetheless, the relatively low energy density of the polymer dielectric limits its application. Herein, sulfobetaine methacrylate (SBMA) was grafted onto poly(vinylidene fluoride) (PVDF) through free-radical polymerization, resulting in the formation of PVDF-g-SBMA. Dielectric films of PVDF-g-SBMA were then fabricated using a casting method. The grafting of SBMA enhances the polarization of the graft copolymer dipoles, its electron-withdrawing ability, and mechanical strength, thereby improving the dielectric characteristics of the copolymer films. At a grafting level of 7 wt %, the copolymer film demonstrates a relatively high dielectric constant (∼11.3) and a high electrical breakdown field strength (∼346 kV/mm) at 1 kHz, representing about a 16% increase in dielectric constant with respect to pure PVDF films (∼9.7) and a 71% increase in breakdown field strength (∼202 kV/mm). At the highest applied field strength, the energy density of the material (∼8.38 J/cm3) is approximately 390% greater compared to pure PVDF films, which exhibit an energy storage density of approximately 1.71 J/cm3. This study offers a practical approach to achieving a high energy storage capacity in polymer-based dielectrics.