Electric Actuation of Liquid Metal Droplets in Acidified Aqueous Electrolyte

The electric actuation of room-temperature liquid metals, such as Galinstan (gallium-indium-tin), has largely been conducted in alkaline electrolyte. Addition of surface-active anions and a proper acidic pH are expected to influence the interfacial tension of the liquid metal due to a high surface charge density. Hence, it should be possible to actuate liquid metals in such acidic environments. To ascertain this, at first, the dependence of the interfacial tension of Galinstan in NaOH, acidified KI, and acidified NaCl electrolyte on the concentration of the surface-active anions OH-, I-, and Cl-, respectively, were studied. Subsequently, a systematic study of the actuation of Galinstan in acidified KI electrolyte was executed and compared to actuation in alkaline medium. In the presence of HCl and acidified NaCl electrolyte, the interfacial tension of Galinstan is only marginally altered, while acidified KI solution reduced the interfacial tension of Galinstan significantly from 470.8 +/- 1.4 (no KI) to 370.6 +/- 4.1 mN/m (5 M KI) due to the high surface charge density of the electric double layer. Therefore, in acidified electrolyte in the presence of surface-active anions, the electrically actuated motion of LM can be realized. In particular, the actuation of Galinstan achieves a higher average and maximum speed at lower applied voltage and power consumption for acidified KI electrolyte. The formation of high surface charge density in acidified environments signifies a paradigm shift and opens up new possibilities to tune interfacial tension and controlled LM droplet motion of room-temperature liquid metals.

室温液态金属（如镓铟锡合金）的电驱动大多是在碱性电解液中进行的。由于表面电荷密度较高，添加表面活性阴离子以及合适的酸性pH值预计会影响液态金属的界面张力。因此，在这种酸性环境中驱动液态金属应该是可能的。为了确定这一点，首先分别研究了镓铟锡合金在氢氧化钠、酸化碘化钾和酸化氯化钠电解液中的界面张力对表面活性阴离子OH⁻、I⁻和Cl⁻浓度的依赖性。随后，对镓铟锡合金在酸化碘化钾电解液中的驱动进行了系统研究，并与在碱性介质中的驱动进行了比较。在盐酸和酸化氯化钠电解液存在的情况下，镓铟锡合金的界面张力仅有微小变化，而酸化碘化钾溶液由于双电层的高表面电荷密度，使镓铟锡合金的界面张力从470.8±1.4（无碘化钾）显著降低到370.6±4.1毫牛/米（5摩尔/升碘化钾）。因此，在存在表面活性阴离子的酸化电解液中，可以实现液态金属的电驱动运动。特别是，对于酸化碘化钾电解液，镓铟锡合金的驱动在较低的施加电压和功耗下实现了更高的平均速度和最大速度。在酸性环境中高表面电荷密度的形成意味着一种范式转变，并为调节室温液态金属的界面张力和控制液态金属液滴运动开辟了新的可能性。