Smooth Transportation of Liquid Metal Droplets in a Microchannel as Detected by a Serially Arranged Capacitive Device

Gallium alloy liquid metals (Ga-LMs) possessing fluidity, electric conductivity, and low toxicity are attractive for use in flexible devices and microfluidic devices. However, the oxide skin of Ga-LMs in the atmosphere adheres to the microchannel surface, preventing the transportation of Ga-LMs in the channel. We introduced liquid with Ga-LMs into a channel with a radius of 500 µm to prevent the oxide skin of the Ga-LM from adhering to the channel. Then, we found that the cylindrical shape of the channel enabled smooth transportation of Ga-LMs independently of both the liquid and the channel material. The liquid introduced with Ga-LMs not only prevents adhesion but also improves the spatial controllability of Ga-LMs in the channel. We can control the position of Ga-LMs with 100 µ m resolution using highly viscous (> 10 cSt) liquid. In addition, we combined the microchannel with patterned electrodes, fabricating a serially arranged capacitive device. The local capacitance detected by the patterned electrodes changed by more than 6 % via the smooth transportation of Ga-LMs. The analysis results based on an equivalent circuit quantitatively agree with our experimental results. We can modulate the serially arranged capacitors using the smooth transportation of Ga-LMs in the channel.