Remarkable enhancement of mechanical and dielectric properties of flexible ethylene propylene diene monomer (EPDM)/ barium titanate (BaTiO₃) dielectric elastomer by chemical modification of particles

In this study, three types of coupling agent, titanium tris(dodecylbenzenesulfonate) isopropoxide (NDZ 109), γ-methacryloxypropyltrimethoxysilane (KH570) and vinyltrim + ethoxysiloxane homopolymer (SG-Si6490), were utilized to reduce the polar surface energy of barium titanate (BaTiO₃) particles from 37.53 mJ m^-2 to 0.77 mJ m^-2, 16.52 mJ m^-2 and 5.46 mJ m^-2, respectively. At 30 vol% filler loading, NDZ 109 treated BaTiO₃ with the lowest polar surface tension exhibited a remarkable compatibility with ethylene propylene diene monomer (EPDM) gum shown by the bound rubber content. It is found that just 1% (by weight of BaTiO₃ amount) coupling agents SG-Si6490 can raise the tensile strength of EPDM with untreated BaTiO₃ composite from 1.94 MPa to 9.00 MPa, due to the C=C bonds from vinyl groups. In terms of electrical properties, when untreated BaTiO₃ loading was 30 vol%, the dielectric constant of EPDM control can increase from about 2 to 7. Moreover, the SG-Si6490 treated BaTiO₃ further improved the dielectric constant of EPDM with untreated BaTiO₃ composite from 7 to around 8. EPDM with NDZ109 treated BaTiO₃ composite exhibited the lowest volume resistivity among EPDM composites.