Due to very high surface tension, when small pools of an alloy of gallium and indium are immersed in water they quickly organize themselves into spheres. No More!
Professor Michael Dickey's research group has developed a technique for controlling the surface tension of the liquid metal by applying very low voltages, opening the door to a new generation of reconfigurable electronic circuits, antennas and other technologies. The technique hinges on the fact that the oxide "skin" of the metal - which can be deposited or removed - acts as a surfactant, lowering the surface tension between the metal and the surrounding fluid.
According to Dr. Dickey, "......we discovered that applying a small, positive charge - less than 1 volt - causes an electrochemical reaction that creates an oxide layer on the surface of the metal, dramatically lowering the surface tension from 500 mN/meter to around 2 mN/meter...... This change allows the liquid metal to spread out like a pancake, due to gravity." The change in surface tension is reversible, so when the polarity of the charge is flipped from positive to negative, the oxide is eliminated and high surface tension is restored. The surface tension can be tuned between these two extremes by varying the voltage in small steps.
A paper describing the work, "Giant and Switchable Surface Activity of Liquid Metal via Surface Oxidation," was published in the Proceedings of the National Academy of Sciences. Lead authors of the paper are graduate students Mohammad Rashed Khan and Collin Eaker. The paper was co-authored by Dr. Edmond Bowden, a professor of chemistry at NC State. Dr. Dickey is the senior author. The work is supported by a grant from the National Science Foundation.
In mid-October, "Shape Configurable Liquid Metal", a YouTube video demonstration of the technique, had logged nearly 440,000 hits