Shell-Mediated Deformation and Fracture Behavior of Liquid Metal Particles for Mechanoresponsive Electronics

Responsive materials utilizing room-temperature liquid metals (LM) are gaining strong interest in flexible electronics, 3D printing, and biomedical therapeutics. The facile production of LM core-shell particles is enabled through the rapid formation of a passivating surface oxide that prevent LM droplets from coalescing. Rupturing these oxides can facilitate mechanically-responsive switching from electrically insulating to conducting states. While the relative ease of gallium oxide deformation is attractive for intrinsically stretchable electronics, the oxide shell dominates much of the LM mechanical behavior. Previous works show that this oxide matures over time under ambient conditions, which can increase the stiffness of the LM particles.¹ Chemical functionalization of LM particles have demonstrated ways to disrupt the oxide formation or hinder its growth.² However, the lack of complete control over the LM oxidation may introduce mechanical hysteresis into these materials systems. Furthermore, environmental conditions and dynamics of particle strain also play a large role in influencing this hysteresis. Therefore, having an improved understanding on the influencing factors towards LM particle rupture can potentially improve efforts in controlling its mechanical response. In this work, we demonstrate the deformation and fracture behavior for single-particles of eutectic Ga-In (eGaIn) alloy under variable conditions. Through in situ compression testing, this investigation focuses on the effects of 1) oxygen content, 2) compression rate, and 3) particle coatings that influences the eGaIn mechanical behavior. By coating eGaIn with materials having well-known mechanical properties (i.e., silica), we can supersede the properties of the gallium oxide and develop LM particles with predictable and tunable mechanical behavior under ambient conditions. Compared to oxide-coated eGaIn, SiO₂-eGaIn particles fracture in an abrupt and brittle manner. The silica shell thickness can be modified to change the mechanical properties of eGaIn particles as desired. With controllable stiffness and fracture behavior that is not dependent on the environmental conditions, these modified eGaIn particles can be explored for a variety of mechanoresponsive applications including pressure-sensitive solders or sensing devices.<br/>Farrell, Zachary J., and Christopher Tabor. "Control of gallium oxide growth on liquid metal eutectic gallium/indium nanoparticles via thiolation." Langmuir 34.1 (2018): 234-240.<br/>Morris, Nicholas J., Zachary J. Farrell, and Christopher E. Tabor. "Chemically modifying the mechanical properties of core–shell liquid metal nanoparticles." Nanoscale 11.37 (2019): 17308-17318.