Mechanical, dielectric and actuated properties of carboxyl grafted silicone elastomer composites containing epoxy-functionalized TiO2 filler

Abstract Silicone rubber (SiR) is one of the most promising dielectric elastomer (DE) materials for DE actuator, but it is still limited by low properties such as mechanical strength, dielectric constant and actuated strain at low electric fields. In this study, we report the design and preparation of SiR DE composite with simultaneously improved tensile strength, dielectric constant and actuated strain at low electric fields by introducing both polar functional group and multifunctional filler. Firstly, carboxyl groups were grafted onto polymethylvinylsiloxane (PMVS) by using a radical-mediated thiol-ene click reaction to improve the dipole polarizability. Meanwhile, epoxy group-functionalized TiO2 (E-TiO2) particles as multifunctional fillers were prepared and filled into carboxyl groups modified PMVS (PMVS-COOH). The esterification reactions between carboxyl groups of PMVS-COOH and epoxy groups of E-TiO2 results in interfacial covalent cross-linking, good interfacial interaction, and strong interfacial polarizability of E-TiO2/PMVS-COOH dielectric composites. As a result, the tensile strength largely increases from 0.33 MPa to 0.89 MPa as the content of E-TiO2 increases from 10 phr to 30 phr. The dielectric constant at 103 Hz of the composite with 30 phr E-TiO2 reaches 8.98, which is 3.3 times as reference SiR due to the simultaneously improved dipole and interfacial polarizability. The actuated strain at low electrical field (15 kV·mm-1) of the composite with 30 phr E-TiO2 reaches 3.7% without any pre-strains, which is 5.2 times than that of reference SiR. Our study provides a simple and effective strategy to simultaneously improve the mechanical, dielectric and actuated properties of SiR DE.