Physics Colloquium: Fingers and Fractals in Liquid Metals
March 10 @ 4:00 pm
North Carolina State University, Department of Physics
Abstract: A droplet of pure water placed on a clean glass surface will spread axisymmetrically, and a droplet of mercury will bead up into a spherical droplet. In both cases, the droplet is minimizing its surface energy — creating an object with a minimized surface area — and there is nothing to break the symmetry. Remarkably, droplets of the room-temperature liquid gallium-indium (EGaIn), which like all metals have an enormous surface tension, can nonetheless undergo fingering instabilities in the presence of an oxidizing voltage. I will describe how this oxide acts like a reversible surfactant, generating fingering instabilities, tip-splitting, and even fractals through Marangoni instabilities. Remarkably, we find that EGaIn droplets placed in an electrolyte under an applied voltage can achieve near-zero surface tension. Furthermore, at larger voltages, we observe a re-entrant surface tension driven by oxidative stresses. Quantitative control of these effects provides a new route for the development of reconfigurable electronic, electromagnetic, and optical devices that take advantage of the metallic properties of liquid metals.
Bio: Karen Daniels is a Professor of Physics at NC State University. She received her BA in Physics from Dartmouth College in 1994, taught school for a few years, and then pursued a PhD in Physics at Cornell University. After receiving her doctorate in 2002, she moved to North Carolina to do research at Duke University and then joined the faculty at NC State in 2005. Her lab at NC State investigates a number of problems in the deformation and failure of materials, from fluid flows, to piles of sand, to fracturing gels. When not working with her students on experiments in the lab, she likes to spend time in the outdoors, which has led her to contemplate the implications of her research for geological and ecological systems. In 2011-2012, she received an Alexander von Humboldt fellowship which allowed her to spend the year conducting research in Göttingen, Germany.