UNS: A Fundamental Study of Reversible and Giant Surface Activity on Soft Metals

1510772 - Dickey

This award supports fundamental research on a new class of surfactants that can be controlled electrically to manipulate the shape and flow of liquid metals. These liquid metals are based on alloys of gallium and provide a low-toxicity alternative to mercury, which is a common liquid metal that has been limited historically by its toxicity. These metals are liquids like water, yet have electrical properties similar to metals. This combination of properties could enable electronic devices that are soft, stretchable, or shape-reconfigurable. The proposed work focuses on a new method to control the shape of liquid metals by utilizing electrical signals to control the surface properties of the metal and thereby manipulate the liquid metal at small length scales. The ability to control the shape or flow of metals using low voltages may enable new types of switches, antennas, wires, and electronics.

The scientific goals focus on understanding this new method to control the interfacial tension of liquid metal via electrochemical deposition (or removal) of an ultra-thin oxide layer on its surface. Unlike conventional surfactants (e.g., soaps or detergents), this approach can tune the interfacial tension of liquid metal significantly (from ~500 mN/m to near zero), rapidly, and reversibly using only modest voltages (~1 V). The proposed work seeks to understand this complex interfacial system by characterizing the role of the surface oxide on interfacial tension through three tasks. These studies will provide new fundamental understanding of soft material interfaces and in turn, help extend this phenomenon to other materials that form surface oxides as well as enable entirely new micro-scale phenomena involving shape reconfigurable metals using low voltages. The work will also establish the importance of surface oxides as a new class of fluid surfactants, which bring about some of the largest changes in surface tension ever reported.

The project will produce new techniques to control the shape of liquid metals and thereby enable new types of reconfigurable optics, microfluidics, and electronics. It will also lay the foundation for new, innovative opportunities for the use of liquid metals that go beyond toxic mercury.

The research will be integrated with an outreach module called 'The Science of the Terminator' that describes liquid metals within the context of the popular motion picture. A partnership with the Engineering Place at NC State will ensure that the presentations are appropriately targeted and widely disseminated. The project will integrate undergraduate, high school, and exchange students on research projects and will continue to do so with this project by using the visually appealing nature of this project to attract students.