Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature
Title: Eutectic Gallium-Indium (EGaIn): A Liquid Metal Allloy for teh Formation of Stable Structures in Microchannels at Room Temperature
Authors: Michael D. Dickey, Ryan C. Chiechi, Ryan J. Larsen, Emily A. Weiss, David A. Weitz, and George M. Whitesides
Source: Advanced Functional Materials 2008, 18, 1097-1104 
Eutectic gallium-indium is an electrically conductive liquid metal at room temperature used in microfluidic devices to make microscale electronics and electromagnets. Interestingly, for small surface stresses, the fluid behaves as an elastic solid, but readily flows once enough stress is applied to the surface. Because of this property, eutectic gallium-indium can be forced through microfluidic channels by applying a pressure, like any other fluid, but once the pressure is relieved, the gallium-indium alloy remains structurally stable.
The rheological properties of the gallium-indium alloy are thought to be caused by the unusual surface of the alloy. In air, the alloy will spontaneously develop a “skin” composed mostly of gallium oxide, which confines the liquid gallium-indium alloy beneath it. The gallium oxide skin also acts as a surfactant, which serves to lower the surface tension of the material.