Liquid Metal Insclusions For Dielectric Elastomers Based Sensor And Its Properties

Polymetric material is widely used in the field of flexible electronics due to its great ductility.However,its poor conductive and dielectric properties fail to meet the demand in these electronics.As a result,it's a common method to improve its properties by adding conductive inclusions to polymer.Ga In alloy is an ideal filling material because it has decent conductivity,what's more,it is liquidus at room temperature and non-toxic.Here we use such metal to fabricate dielectric elastomer and sense outside stress by taking advantage of its unique conductivity and fluidity.We can fabricate composite films by mixing the liquid metal with three different kinds of silicone materials: Ecoflex,Vytaflex and PDMS.After the mixture is heated and cured,we can obtain the elastomer with both good mechanical and electrical properties.After analyzing the interfacial metallograph,we can understand the distribution of liquid droplets inside the composite film.The mechanical properties of different films are analyzed and the results suggest that liquid inclusions have no negative influence on the ductility of polymetric substrates.In common cases,the ductility will increase when liquid inclusions are added.According to the theoretic model,the Young's modulus was mainly decided by the surface tension of Ga In,average size of droplets and the volume ratio of the liquid metal.Based on the conductivity of composite films,it is found that the composite material is almost insulate and the conductivity has nothing to do with the ratio of liquid inclusions.Unlike common conductors,the resistance of composite films may decrease or remain the same during stretch,also,different films may have different resistance changes under compression.Parallel-plate capacitors are fabricated and the films act as the dielectric layer.We found that the capacitance of capacitors increases under compression yet the value remains still when capacitors are stretched.We came up with the effective medium theory and compared the theoretic results to the experimental results.Sensors that can sense the three-dimensional forces were designed and fabricated.The resistance of composite films is designed as the sensing unit for vertical compression,the capacitance of parallel Ga In is designed as the sensing unit for horizontal stretch.The sensing unit can be changed in order to change the sensitivity of the sensor.We designed different structures for different sensitivities and analyzed the capacitance of different structures.