Preparation Of Epoxy Natural Rubber Dielectric Elastomer Composites And Their Actuation Performance

Dielectric elastomers（DEs）,as a class of electroactive polymers（EAP）exhibiting special electrical properties,are regarded as substitutes for“artificial muscle”due to their characteristics in terms of large strains,fast response,and good durability.A dielectric elastomer actuator（DEA）is fabricated when the DE is sandwiched between two flexible electrodes,which can convert electrical energy into mechanical energy.DEA exhibits numerous advantages,including a simple structure,small size,large conversion efficiency,and large deformation abilities,therefore it can be widely used in biomimetic robots,micro-optical zoom lenses,loudspeakers,microfluidic devices,and tactile devices.However,the DEA typically operates close to the dielectric breakdown to obtain a large deformation,which easily results in a“pinhole”defect in DE films and loses their function,which limits its use in real life.In this paper,dielectric nano-fillers with different core-shell structures were designed to enhance the electromechanical properties of epoxy natural rubber（ENR）with a high actuated strain at low driving voltages.The details are as follows:（1）Barium titanate（BTO）dielectric nanoparticles were covalently modified with 3-mercaptopropyl ethoxydi（trialkyl-pentaethoxy）silane（Si747）to obtain a core-shell Si747@BTO dielectric nanoparticles,which was then dispersed in ENR matrix to prepare dielectric elastomer composites.The addition of Si747 enhanced the dispersion of BTO dielectric nanoparticles in the ENR matrix,promoting the enhancement of interfacial polarization in the composites,which led to a significant increase in the dielectric constant.Furthermore,a polar plasticizer with epoxy soybean oil（ESO）was filled into ENR composites to reduce their elastic modulus,leading to a highβ(11.4 MPa^-1).Finally,the 50 phr ESO/Si747@BTO/ENR exhibited a relatively high actuated strain of 8.89%at 22 k V/mm,a value about 5.1-fold higher than that of pure ENR（1.45%）under the same electric field.Moreover,the ENR based DEA exhibited good stability during cycling actuation,demonstrating the potential in practical applications.（2）The TiO₂ nanoparticles was first non-covalent modification by tannic acid（TA）,which was further covalent bond modified by Si747 to obtain a core-shell TiO₂@Si747-TA dielectric particles.Due to the TA insulation layer,the surface structure of TiO₂ dielectric nanoparticles was not destroyed,while the interfacial compatibility between TiO₂ filler and ENR matrix was improved by Si747.Finally,the interfacial polarization of ENR composites was effectively enhanced,resulting in a high dielectric constant.Furthermore,the reinforcement effect of filler network in ENR composites was effectively weaken by addition of polar plasticizer of ESO,leading to a reduced elastic modulus and a highβ(16.57 MPa^-1).As a result,the actuated strain of 50 phr ESO/TiO₂@Si747-TA/ENR composites reached 12.73%at 20 k V/mm,which was 9.4 times higher than that of pure ENR（1.22%）at the same electric field.Moreover,good durability and mechanical properties were displayed by the as-prepared ENR based DEA,which is of great importance for their long-term using.（3）The carbon nanotubes（CNTs）were firstly non-covalent modification with polydopamine（PDA）,which was further covalent bond modified with Si747 to prepare PDA-Si747@CNT dielectric nanoparticles.PDA insulation ensured that the surface structure of CNT was not damaged,while the Si747 provided covalent bonding between CNT and ENR,resulted in the good dispersion of CNT in ENR matrix.In addition,the insulating layer of PDA-Si747 reduced the electrical conductivity of CNT,which maintained the good insulating properties and a high dielectric breakdown of ENR composites.Finally,the maximum actuated strain of PDA-Si747@CNT/ENR composites increased to 17.9%at 55.5 k V/mm,which was 152%higher than that of the CNT/ENR composites（7.1%at 30k V/mm）.More importantly,the ENR based DEA demonstrated excellent stability and reliability,which was advantageous for practical applications.