Synthesis and Self-Assembly of Diborate Ester Polymers for Dielectric Elastomer Actuators

Inorganic nanoparticles have been widely used as fillers to modify dielectric elastomers to simultaneously improve mechanical and dielectric performances. Elegant interface design is crucial for achieving synergy between fillers and elastomers. Herein, we show that diborate ester polymers can both improve the interfacial compatibility between inorganic nanoparticles and elastomers and enhance the dielectric performances. The diborate ester polymers are derived from the condensation reaction between tetrakis(dimethylamino)diborane (or tetrahydroxydiborane) and a three-armed catechol monomer. Choosing TiO2 nanoparticles as the inner core, a series of TiO2@diborate ester polymer core-shell nanoparticles are synthesized. Density functional theory (DFT) calculations indicate that the diborate ester polymer shell tightly bonds to the surface of TiO2 through two dissociative bidentate bridging modes of the catechol monomer (absorption energy: -11.049 eV). These core-shell nanoparticles can soften and tough polydimethylsiloxane (PDMS) and show enhanced interfacial binding affinity to PDMS than naked TiO2 nanoparticles. The fabricated composites have high dielectric constants (up to 6.8) and low dielectric losses (<0.03). The actuated strain and puncture voltage of the composites reach 25.9% and 80 V mu m(-1), respectively, which are much higher than those of PDMS and TiO2/PDMS. This work provides a promising route to fabricate core-shell nanoparticles for high-performance dielectric elastomers.