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 spherical 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 self-assembling 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.