Fluidic-enabled formation of EGaIn capsules and droplets with tunable surface chemistry and electromechanics

The combination of high electrical conductivity and fluidity and biocompatibility exists in liquid metals including eutectic gallium-indium (EGaIn) but their application remains restricted because of spontaneous oxide development and unstable flow behavior. Here we describe a microfluidic method to create EGaIn droplets and capsules with adjustable dimensions and mechanical and surface properties. The acidity level of the suspending fluid, ethanol, determines whether EGaIn will create oxide-covered capsules or non-oxidized liquid droplets. The oxide coating stabilizes aspherical shapes, which deform irreversibly. Droplets readily reform into spheres after applied stress is removed, but are susceptible to coalescence. A thiolated PEG-click complex forms selfassembling structures at metal-liquid interfaces to protect droplets from merging while allowing surface modification. When cast in thin films, the fluidic-generated EGaIn structures exhibit different electromechanical responses: oxide-coated capsules function as field-effect elements while thiol-stabilized droplets operate as ohmic conductors. By integrating microfluidic generation, shape programmability, and chemical stabilization, we open new pathways to multifunctional liquid-metal architectures with controllable electromechanical response. in thin films using four-point probe measurements. 176 In this work, we establish a unified microfluidic plat-177 form for microscale EGaIn formulations that enables si-178 multaneous control over droplet size, shape, mechani-179 cal response, and surface functionalization. By chemi-180 cally modulating pinch-off conditions, we generate tun-181 able droplets or capsules, assess mechanical reversibility 182