Interfacial Tension Hysteresis of Eutectic Gallium‐Indium

Abstract

When in a pristine state, gallium and its alloys have the largest interfacial tensions of any liquid at room temperature. Nonetheless, applying as little as 0.8 V of electric potential across eutectic gallium indium (EGaIn) placed within aqueous sodium hydroxide (NaOH, or other electrolyte) solution will cause the metal to behave as if its interfacial tension is near zero. The mechanism behind this phenomenon has remained poorly understood because NaOH dissolves the oxide species, making it difficult to directly measure the concentration, thickness, or chemical composition of the film that forms at the interface. In addition, the oxide layers formed are atomically‐thin. Here, it presents a suite of techniques that allow to simultaneously measure both electrical and interfacial properties as a function of applied electric potential, allowing for new insights into the mechanisms, which cause the dramatic decrease in interfacial tension. A key discovery from this work is that the interfacial tension displays hysteresis while lowering the applied potential. It combines these observations with electrochemical impedance spectroscopy to evaluate how these changes in interfacial tension arise from chemical, electrical, and mechanical changes on the interface, and close with ideas for how to build a free energy model to predict these changes from first principles.

Interface of gallium-based liquid metals: oxide skin, wetting, and applications

“…Interestingly, when the metal oxidizes electrochemically, the effective tension drops significantly beyond that predicted by Lippman's equation. 105 The term ‘effective tension’ is utilized because the interface contains a thin layer of oxide species and is therefore not a pure liquid–fluid interface. The role of electrochemical oxidation has been reviewed elsewhere and is briefly highlighted here.…”