Eutectic Gallium‐Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature

TLDR

The study investigates the rheological behavior of liquid metal eutectic gallium‑indium (EGaIn) when injected into microfluidic channels to form stable microstructures at room temperature. EGaIn behaves elastically until a critical surface stress is reached, then yields and flows, allowing rapid filling of microchannels under pressure while maintaining structural stability when pressure is removed. Experiments reveal that the critical surface stress (~0.5 N/m) required for EGaIn to flow is governed by its surface oxide layer and is inversely proportional to the smallest channel dimension, informing future microfluidic design.

Abstract

Abstract This paper describes the rheological behavior of the liquid metal eutectic gallium‐indium (EGaIn) as it is injected into microfluidic channels to form stable microstructures of liquid metal. EGaIn is well‐ ;suited for this application because of its rheological properties at room temperature: it behaves like an elastic material until it experiences a critical surface stress, at which point it yields and flows readily. These properties allow EGaIn to fill microchannels rapidly when sufficient pressure is applied to the inlet of the channels, yet maintain structural stability within the channels once ambient pressure is restored. Experiments conducted in microfluidic channels, and in a parallel‐plate rheometer, suggest that EGaIn's behavior is dictated by the properties of its surface (predominantly gallium oxide, as determined by Auger measurement s); these two experiments both yield approximately the same number for the critical surface stress required to induce EGaIn to flow (∼0 .5 N/m). This analysis–which shows that the pressure that must be exceeded for EGaIn to flow through a microchannel is inversely proportional to the critical (i.e., smallest) dimension of the channel–is useful to guide future fabrication of microfluidic channels to mold EGaIn into functional microstructures.