Dimensional limitation of polymeric microfluidic platform for liquid metal manipulation

We report a study on the minimum microfluidic channel dimension in which gallium-based liquid metal alloy can be filled. Based on the non-toxicity of gallium-based liquid metal, it was expected to be utilized in many applications. Specifically, in order to possess advantages of its liquid property, there are several efforts to use it in microfluidic-based applications. However, due to its high surface tension of the liquid metal, the applicable dimension of the microfluidic channel has been simply limited. In order to investigate the minimum channel dimension, we have fabricated three different thick (5, 10, and 25 μm) PDMS-based microfluidic channel with various widths in the range from 20 μm to 3 μm using SU-8 mold technique. We successfully filled the liquid metal into as small as 3 μm wide channel with 25 μm thickness which has a rectangle cross section of 75 μm². As a demonstration of the filling of liquid metal, we transferred the shape of channel in which liquid metal is filled, to positive photoresist by liquid metal-based photolithography.