C. Liu, J. Ding
New York State College of Ceramics at Alfred University,
United States
Keywords: Stretchable electronics, liquid metal, composites, hierarchical structure
Summary:
Gallium-based liquid metal (LM) alloy is a promising material in applications such as flexible electronics and thermal management due to its outstanding electrical conductivity, thermal conductivity, and reconfigurable under harsh stretching conditions. Polymeric elastomers are extensively used as matrix materials to embed LM reinforcement to form composites for better electromechanical performance. Polydimethylsiloxane (PDMS) is a widely used elastomer due to its stretchability, biocompatibility, and moldability. Research has shown that PDMS/LM composites demonstrate excellent electrical conductivity and robust elasticity as flexible conductors and strain sensors. LM particles are homogeneously dispersed in the PDMS matrix, which demonstrates an isotropic performance of electrical conductivity. However, these composites usually require mechanical activation process to create electrically conductive channels in the composites. In addition, little research has focused on forming non-uniform structures for an anisotropic electrical property which is required in many electrical devices. In this work, we fabricate an inhomogeneous PDMS/LM composite with a hierarchical structure. The hierarchical structure is formed by the self-assembly of LM droplet. LM droplets sink down and deposit on the bottom of each layer due to a larger density compared to PDMS. The influence of the LM concentration, LM droplet size, sinking down time, and viscosity of PDMS on the sedimentation process of LM droplets is studied. The deposited LM layers demonstrate a larger local density of electrical pathways compared to structures with homogeneous dispersion. Therefore, the hierarchical PDMS/LM composite demonstrates a better electrical conductivity on the bottom surface, but nonconductivity between top and bottom surface. The tensile and electromechanical testing are performed to investigate the mechanical strength and the electrical conductivity of the composites. The hierarchical PDMS/LM composite can be used as a wearable electronic due to its stretchability and electrical conductivity.