Preparation And Properties Of Stretchable Liquid Metal/Polyurethane Conductive Elastomer Composites

Highly stretchable conductors have many potentials applications,such as wearable electronic devices,soft robots and artificial electronic skins.Researchers have developed many high-performance stretchable conductors,including wavy conductive wires or membranes in flexible substrates,conductive fillers mixed or deposited in rubber,and three-dimensional (3D) conductive components in flexible substrates.However,structural design of the metal and elastomer matrix can only increase the stretchability of the conductor limitedly;However,the stretchability of the conductor increase limitedly,the loss of stretchability and elasticity and nanofiller network can easily be damaged under tensile strain after assembling a rigid conductive filler to the matrix.Although these problems can be partially solved by using low-melting liquid metal (LM) as the conductive filler,the complex injection process,the large consumption of expensive LM and the leakage of liquid metal still limit its application in large-scale.In this work,liquid metal nanoparticles (LMNPS) is self-assembled on 3D polyurethane sponge (PUS) modified by polydopamine(PDA) and then is mechanically sintered to prepare stretchable flexible conductive composites.The work content is as follows:(1)LMNPS was prepared by ultrasonic treatment and modified with different mercapto coupling agents,and we found that The average particle size of LMNPS is 111?559nm,the surface of LMNPS is 2.5?4.7nm oxide layer,and the outer layer is SAM of the mercapto coupling agent.When the liquid metal is broken by ultrasonic treatment,there is a competition between the oxidation process and the formation of SAM.The surface properties of LMNPS are determined by SAM.Futher,the dependence of particle size on the preparation process conditions was also studied:short-chain coupling agents will weaken the oxidation process and easily fuse the nanoparticles cause the average particle size increasing.The formation of SAM by a long-chain coupling agent takes a relatively longer time than the formation of an oxide film,and average particle size of LMNPS is easy to decrease An appropriate liquid metal concentration makes LMNPS smaller.There is an equilibrium process during ultrasonic treatment.If the equilibrium is not reached,extending the ultrasound time helps reduce the particle size.(2) Stretchable conductive elastomer composites were prepared based on mercapto coupling agent modified LMNPS and polydopamine modified polyurethane sponge elastomer.Polydopamine modified polyurethane sponge elastomer is used as the matrix,the thiol group of the LMNPS surface coupling agent coordinates with the liquid metal surface oxide layer,and the other end of the coupling agent has a hydrogen bond with the hydroxyl group and the amine group on the surface of the polydopamine.LMNPS self-assembles on the surface of polyurethane sponge to form a dense and uniform layer of LMNPS.Futher,a continuous conductive network of 3D PUS-PDA coated by 2D LM layer was successfully obtained by mechanical sintering(3) The number of immersion in the LMNPS dispersion by sponge was used to control the LM content and control the electrical conductivity of the composites.The highest electrical conductivity of composites reached 478S cm-1.The conductivity stability of the stretchable conductive elastomer composite was further explored.It was found that when the LM content is 15.4 mg mg-1,the ?R/R0 of the composite is only 2% at 50% strain,indicating that it has a high conductivoty stability.In addition,the composite exhibits good electrical conductivity stability under small deformations such as compression cycles,small strain stretching (?30%),bending,and bending cycles:its maximum ?R/R0 is only 0.02-0.06.we also found that the interface design helps to reduce the LM leakage of the composites under compression and other strain,and the LM leakage of the matrix in the composite material after polydopamine treatment is lower.