Piezoresistance Property Of Imidazolium-ionic Liquid Modified Carbon Black/silicone Rubber Composite

With the development of robotic, wearable electronic devices and smart fiber,the application of flexible piezoresistive sensor material is more and more highlighted.Carbon black/silicone rubber composites, as a kind of effective piezoresistive sensor material, benefit from the silicone rubber matrix for good flexibility, chemical stability and resistance to high and low temperatures. Carbon black worked as conductive filler and formed conductive network in the matrix, which gived the composite material piezoresistive sensitivity. Improving the dispersion of carbon black in the silicone rubber matrix by physical and/or chemical methods can improve the composite's conductive,piezoresistive sensitivity and cyclic repeatability,reduce the sensing time lag, which will finally improve the performance of sensing materials and expand its application field.To improve the dispersion of conductive carbon black in silicone rubber, this article respectively used 1-hexadccyl-3-methyl imidazole bromine([C16MIm]Br) and1-allyl-3-methyl imidazole chloride ([AMIm]Cl), two kinds of ionic liquids for conductive carbon black surface modification by physical grinding method. Surface hydrophobic modified silica as a reinforcing filler is also used to adjust the elastic modulus and piezoresistive sensitivity of the sample. By two-roll mixing, high temperature vulcanization and post-vulcanization, a series of electric conductive silicone rubber samples with different conductive filler content are prepared. Carbon black dispersion were characterized by SEM. Digital multimeter and high insulation resistance meter are used to measure the conductivity of the samples. A combination of material universal testing machine, digital multimeter and cylinder electrodes is used to carry out the piezoresistive test, piezoresistive relaxation test and cycle-run test.Results showed that the dispersion of carbon black with two kinds of ionic liquid modified were increased. The electric conductivity and piezoresistive sensitivity of the sample are also enhanced. A spring-dashpot model is used to fit the piezoresistive process. Fitting results showed that the way resistance change in this process is similar to the stress relaxation behavior of elastic polymer, and the fitting parameters showed that the ionic liquid modification decreases the resistance relaxation time of samples, which reduced the sensing time lag. In a 10-times cyclic compression test,carbon black samples. and hexadecyl ionic liquid modified carbon black samples showed a trend of gradual decline in maximum resistance, which allyl ionic liquid modified samples remained basically unchanged and the piezoresistive cycle repeatability of the material is improved. Surface hydrophobic modified silica can adjust the material hardness and elastic modulus by formula, and then change the sensor sensitivity and range. With the adding of silica, the elastic modulu of sample was increased and the positive piezoresistive response is weakened. That made sample piezoresistive sensitivity reduced and the range widen. Silica can also reduce the piezoresistive relaxation time, and with the synergy effect of allyl ionic liquids,further reducing is performed.