Liquid metals exhibit remarkable mechanical properties, in particular largesurface tension and low viscosity. However, these properties are greatlyaffected by oxidation when exposed to air. We measure the viscosity, surfacetension, and contact angle of gallium (Ga) and a eutectic gallium-indium alloy(eGaIn) while controlling such oxidation by surrounding the metal with an acidbath of variable concentration. Rheometry measurements reveal a yield stressdirectly attributable to an oxide skin that obscures the intrinsic behavior ofthe liquid metals. We demonstrate how the intrinsic viscosity can be obtainedwith precision through a scaling technique that collapses low- andhigh-Reynolds number data. Measuring surface tension with a pendant dropmethod, we show that the oxide skin generates a surface stress that mimicssurface tension and develop a simple model to relate this to the yield stressobtained from rheometry. We find that yield stress, surface tension, andcontact angle all transition from solid-like to liquid behavior at the samecritical acid concentration, thereby quantitatively confirming that thewettability of these liquid metals is due to the oxide skin.
展开▼
