Enhanced Dielectric Properties of P(VDF-TrFE-CTFE)/PMMA Composites with MWCNTs@SiO₂ Core–Shell Fillers

Dielectric materials with superior dielectric properties are pivotal for enhancing the performance of electrowetting-on-dielectric (EWOD) devices. In this work, MWCNTs@SiO₂ core-shell-structured fillers were fabricated by coating multiwalled carbon nanotubes (MWCNTs) with a uniform SiO₂ outer layer. This innovative core-shell structure was incorporated into a poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) and poly(methyl methacrylate) (PMMA) organic matrix to fabricate composite films with enhanced dielectric properties. The incorporation of core-shell fillers significantly enhanced the microcapacitor effect and Maxwell-Wagner-Sillars interface polarization. At a low filler loading of 4 wt %, the composite achieved a high dielectric constant of 25.4 (at 100 Hz), representing a 108.2% enhancement compared to the pristine polymer matrix, while maintaining a low dielectric loss as low as 0.05. Furthermore, the SiO₂ shell effectively mitigated inhomogeneous electric field distribution induced by dielectric constant mismatch, reducing field distortion and consequently enhancing the breakdown strength. Notably, under a DC voltage below 50 V, a high contact angle modulation range of 38.3° was achieved, representing a 151.97% enhancement compared to the pristine polymer matrix. These findings provide a new strategy for developing high-performance dielectric materials for EWOD applications.