Improved electromechanical properties of NBR dielectric composites by poly(dopamine) and silane surface functionalized TiO2 nanoparticles

Abstract

In order to obtain a nitrile-butadiene rubber (NBR) dielectric elastomer composite with excellent electromechanical properties, a combination of bio-inspired poly(dopamine) (PDA) deposition and γ-methacryloxypropyl trimethoxy silane (KH570) grafting was proposed to functionalize the surface of titanium dioxide (TiO₂) nanoparticles. Inspired by adhesive proteins in mussels, dopamine self-polymerization was used to deposit a thin adherent PDA film onto the surface of TiO₂. KH570 that contains double bonds was then grafted through the reactions with hydroxyl and indole groups of the PDA surface. The chemical structure and composition of the TiO₂ surface were characterized by XPS, FTIR, and HR-TEM. Because of the introduction of PDA grafted with the KH570 layer, the NBR composites filled with modified TiO₂ displayed better filler dispersion, higher dielectric constant, lower elastic modulus, and higher electric breakdown field compared with composites filled with pristine TiO₂ particles. Finally, a large actuated strain of about 16% at 60 kV mm⁻¹ without any pre-strains was shown by the composite of NBR filled with 20 phr modified TiO₂ particles, which is 53% larger than that of NBR without a filler. The process was fast, simple, efficient, nontoxic, and controllable, which can provide a new universal method for modification of dielectric fillers to improve the dielectric properties and electromechanical properties of dielectric elastomers.