Structural Optimization And Properties Of Barium Titanate/silicone Rubber Dielectric Elastomer Composites

Dielectric elastomers(DEs)are are an emerging class of smart elastomeric materials that can generate large strains under the action of electric fields and have attracted widespread attention.Silicone rubber(SR)is one of the most promising polymer matrixes among DEs because of its fast response,low modulus,and excellent biocompatibility.However,the low dielectric constant(?)and high driving voltage of SR limit its application in the field of DEs.The present work aims to increase the ? and actuated area strain of SR without affecting other excellent properties.In pursuit of this,the introduction of high dielectric constant barium titanate(BT)into SR is a common and reliable method.However,two problems remained with the BT-filled SR composites: 1)Significant increase of the dielectric constant of the composite relies on a high filling degree of BT,and the enhancement is not as good as that of the conductive filler;2)Due to the presence of a large amount of BT particles,they cannot be well-distributed within the matrix,which therefore may lead to deteriorated mechanical properties and lowered breakdown strength of the composites,both of which are unfavorable for practical applications.To solve the above-mentioned two problems,two structural optimization strategies are adopted to ensure the maximum dielectric constant enhancement of SR and improve the dispersion of BT,and ultimately obtain dielectric elastomer composites with excellent overall properties.BT/MWCNT/SR three-phased nanocomposites with BT and multi-walled carbon nanotube(MWCNT)as the fillers and SR as the matrix were prepared via mechanical blending.The introduction of MWCNT can significantly increase the dielectric constant of the composites,but it also leads to an increase in dielectric loss and a decrease in breakdown strength,while BT acts as a physical barrier,effectively hindering the interconnection of MWCNT and preventing the formation of conductive pathways.BT and MWCNT would also form a micro-capacitive structure and generate a synergistic effect,which contribute to the improvement of ? of the composites.The maximum actuated area strain of the BT/MWCNT/SR composites is 5.8%,which is 4.1 times higher than that of neat SR(1.4%).Results show that composite with the highest dielectric constants did not necessarily exhibit the maximum electromechanical strain,indicating that the maximum electromechanical strain of the composites is not determined by one factor,but a combination of various factors.The tea polyphenols-coated BT(BT@TP)/SR composites were prepared by solution mixing method using TP and theophylline as the surface modification agent for BT.The thickness of the TP coating layer has an obvious effect on the dielectric properties of the composites,and the best dielectric properties are obtained when the TP layer is about 3.1 nm thick.Among all,the nanocomposites,the one filled with 40 wt%BT@TP(40 wt% BT@TP/SR)shows the largest dielectric constant of 4.33 at 1 k Hz,which is 10.18% higher than that of the composite filled with 40 wt% BT(3.93)and35.74% higher than that of neat SR(3.19).Furthermore,the maximum actuated area strain of the 40 wt% BT@TP/SR is 9.2%,which is 1.2 times higher than that of the 40wt% BT/SR(7.8%).and 6.6 times higher than neat SR(1.4%).This indicates that the TP coating layer can effectively improve the dispersion of BT and enhance the interfacial interaction between BT and the matrix,which in turn improves the dielectric properties and actuated area strain of the composites.