Graphite induced periodical self-actuation of liquid metal

Abstract

Self-actuation phenomena of liquid metal spheres in NaOH solution, including spreading, oscillating and stretching, induced by graphite alone were demonstrated for the first time. A liquid metal sphere could spontaneously spread on the surface of the graphite once immersed in the NaOH solution. The surface tension gradient on the sphere induced by the graphite/liquid metal galvanic cell was responsible for this deformation. When a liquid metal sphere was leaned against the side of a piece of graphite, it could oscillate periodically. As the sphere contacted the graphite, it rapidly collapsed, while the curvature radius of the sphere at the contact point decreased. Also, as the capillary force imposed on the sphere was larger than the friction force, the sphere recovered its original spherical shape. The surface tension of the liquid metal sphere acted as the restoring force of the oscillatory movement. Further, a phenomenon of resonance could be observed when two spheres were laid respectively on the top and the side of the graphite. The vibration of the top sphere was induced by the vibration of the side sphere. This finding provides a novel enhancement for the fabrication of future liquid metal beating heart systems and graphite/liquid metal-based batteries or machines.