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 similar to 115 degrees) 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.