@article{hillaire_nithyanandam_song_nadimi_kiani_dickey_daniels_2023, title={Interfacial Tension Hysteresis of Eutectic Gallium-Indium}, volume={12}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202311501}, DOI={10.1002/adfm.202311501}, abstractNote={AbstractWhen 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.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Hillaire, Keith D. and Nithyanandam, Praneshnandan and Song, Minyung and Nadimi, Sahar Rashid and Kiani, Abolfazl and Dickey, Michael D. and Daniels, Karen E.}, year={2023}, month={Dec} }
 @article{song_mehrabian_karuturi_dickey_2021, title={Jumping liquid metal droplets controlled electrochemically}, volume={118}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/5.0036416}, DOI={10.1063/5.0036416}, abstractNote={Jumping droplets are interesting because of their applications in energy harvesting, heat transfer, anti-icing surfaces, and displays. Typically, droplets “jump” from a surface when two or more drops coalesce. Here, we demonstrate an approach to get a single droplet of liquid metal (eutectic gallium indium) to jump by using electrochemistry in a solution of 1M NaOH. Applying a positive potential to the metal (∼1 V relative to the open circuit potential) drives electrochemical surface oxidation that lowers the interfacial tension from ∼450 mN/m to ∼0 mN/m. In the low interfacial tension state, the droplet flattens due to gravity. Rapid switching to a negative potential (relative to the open circuit potential) reduces the surface oxide, returning the deformed droplet to a state of high interfacial tension. This rapid change in interfacial tension in the flattened state generates excess surface energy, which drives the droplet to return to a spherical shape with enough momentum that the liquid droplet jumps. This work is unique because (1) the jumping is controlled and tuned electrically, (2) the approach works with a single droplet, (3) it does not require a superhydrophobic surface, which is typically used to prevent droplets from adhering to the substrate, (4) the drops jump through a viscous medium rather than air, and (5) the potential energy obtained by the jumping drops is one order of magnitude higher than previous approaches. Yet, a limitation of this approach relative to conventional jumping drops is the need for electrolyte and a source of electricity to enable jumping. Herein, we characterize and optimize the jumping height (∼6 mm for a 3.6 mm diameter drop) by changing the reductive and oxidative potential and time.}, number={8}, journal={APPLIED PHYSICS LETTERS}, author={Song, Minyung and Mehrabian, Nazgol and Karuturi, Sahil and Dickey, Michael D.}, year={2021}, month={Feb} }