Significantly enhanced dielectric and hydrophobic properties of SiO2@MgO/PMMA composite films

In this article, we provide a feasible method to prepare high-dielectric-constant hydrophobic composite films, which show potential application as the insulator layer in electrowetting devices. SiO2@MgO core–shell nanoparticles were fabricated via a hydrolysis process and embedded into the PMMA matrix. The microstructure of the nanoparticles and the cross-section of the films indicated that a SiO2 coating has successfully been prepared around the MgO particles with a thickness of about 20–30 nm and the nanofillers were homogeneously dispersed in the polymer. Hydrophobic films (contact angle ∼115°) with appropriate glass transition temperature were obtained. The dielectric constant at various frequencies of the functional fillers enhanced with increasing the SiO2@MgO filler content. The results suggested that SiO2@MgO is more effective in increasing the dielectric constant of PMMA when compared with MgO sheets. Typically, the dielectric constant of the PMMA composite filled with 40 wt% SiO2@MgO reaches 19.1 at 40 Hz, in contrast to 9.7 for the composite filled with 40 wt% MgO sheets and 3.8 for pristine PMMA. Also, the composites exhibited low electrical conductivity (≤10−7) even at high frequency. All the improved performances showed potential application in the dielectric layer of electrowetting devices.