Liquid Metal Droplets in Fluid Systems: Geometry, Chemistry, and Surface Energy

The morphology and surface energy of gallium-based liquid metal (LM) droplets are influenced by the oxygen solubility (x_g) of the surrounding liquid. Using a high-speed camera, we captured the pinch-off frames of macroscopic LM droplets in various solvents. The eccentricity of droplets increased sigmoidally with the x_g of the ambient liquid. Anisotropic pear-shaped LM droplets were observed in high-x_g liquids, concomitantly with surface oxidation. To explore small-scale features, we additionally fabricated micro/nanoscale LM droplets via ultrasonication in organic solvent environments and subsequent evaporation of the solvent. Carbon/Oxygen and Carbon/Gallium atomic ratios of LM microdroplets increased with the solvent’s x_g, indicating that oxygen and organic solvent molecules interacted sequentially with LM. The van Oss-Good model was further implemented to determine the polar and nonpolar surface energy components of LM layers with adsorbates. While the polar component made a minor contribution to the total surface energy, the nonpolar component displayed a strong logarithmic relationship with the x_g of the solvent used to treat the LM layer.