Preparation And Study Of High Dielectric Constant Silicone Rubber

Excellent properties,such as electrical insulation,temperature resistance,biocompatibility and processing make silicone rubber have good potential application in the field of cable terminals and dielectric actuators.In cable terminations,it should have high dielectric constant,low dielectric loss and certain mechanical properties.In dielectric actuators,it should have a high dielectric constant while the modulus of elasticity is as low as possible.The dielectric constant of pure silicone rubber is relatively low（generally about 3）,which has become a bottleneck restricting its development.The most effective way to increase the dielectric constant of silicone rubber is to add conductive fillers.Carbon nanotube is a kind of widely used conductive fillers due to their excellent electrical properties and large aspect ratios.It can effectively increase the dielectric constant of materials at lower loadings.However,the dielectric loss and elastic modulus of the silicone rubber containing carbon nanotubes are relatively high,which is not suitable for application.Modification of carbon nanotubes can inhibit the dielectric loss of silicone rubber to a certain extent,but the modification methods reported in the literature have limited effects.Therefore,in the field of carbon nanotube-filled high-dielectric silicone rubber,some new modification methods are urgent needed,which can suppress the dielectric loss and elastic modulus while increasing the dielectric constant of materials.First of all,SiO₂ coated carbon nanotubes MS was prepared by sol-gel method.Then it was added to methyl vinyl silicone rubber（MVQ）to obtain materials which possess high dielectric constant,low dielectric loss and good mechanical strength.The effect of SiO₂ coating on the microstructure and macroscopic properties of composites was investigated and the mechanism was analyzed.It was found that SiO₂ coating could improve the dispersion of carbon nanotubes in the matrix and enhance the interfacial interaction with the matrix.Moreover,the mutual contact between the carbon nanotubes could be effectively blocked,the leakage current was reduced,and the dielectric loss was suppressed.The dielectric properties and mechanical strength of MS/MVQ composites was improved.Compared with unmodified carbon nanotube/MVQ composites,the dielectric constant of MS3/MVQ composite near the percolation threshold increased by 16.3%,tanδdecreased by 35.5%,reaching 25.6 and 0.089respectively.The AC conductivity remained at a low level.And the tensile strength increased by 16.7%,the elongation at break increased by 32.9%,reaching 10.5 MPa and 877%respectively.Then,the vinyl terminated poly methyl phenyl siloxane（VPMPS）coated carbon nanotubes MP were prepared byπ-πinteraction and hydrophobic interaction.The MP/MVQ composites which possess high dielectric constant and loss elasticity modulus were obtained.The effects of VPMPS coating on the microstructure and macroscopic properties of the composites were studied and the mechanism was analyzed.It was found that the VPMPS coating could not only improve the dispersion of carbon nanotubes in the matrix,but also inhibit the generation of leakage current.Moreover,the interaction between the MVQ molecular chains could be weakened,and the plasticization effect could be achieved.The elastic modulus of the composites was lowered,and the motor sensitivity was greatly improved.Compared with the unmodified MWCNT/MVQ-2,the dielectric constant of the MP2/MVQ composite increased by 45.2%,while the elastic modulus decreased by 31.3%,reaching 13.5 and 1.47 MPa respectively.When the filler content was 2.0 wt%,the motor sensitivity factorβwas 9.2,which was 104.4%higher than pure MVQ（4.5）,114.0%higher than unmodified MWCNT/MVQ-2（4.3）,and the dielectric loss was kept at a low level（0.026）.