Abstract
Gallium-based liquid metal can be used as a material for microheaters because it can be easily filled into microchannels and electrified to generate Joule heat, but the liquid metal-based microheater will suffer breakage induced by voids forming within the liquid metal when the temperature normally gets higher than 100 °C. To resolve this problem, a novel liquid metal-based microheater with parallel ventilating side-channels is presented. It consists of a liquid-metal heating channel and two parallel ventilating side-channels. The heating channel is connected with the side-channels by small gaps between polydimethylsiloxane (PDMS) posts. Experimental results show that this novel microheater can be heated up to 200 °C without damage. To explain its excellent performance, an experiment is performed to discover the development of the voids within the liquid-metal heating channel, and two reasons are put forward in this work on the basis of the experiment. Afterward pressing and bending tests are conducted to explore the mechanical stability of the novel microheaters. Finally, the microheaters are applied to warm water to show their good flexibility on non-flat surfaces. In consequence, the novel liquid metal-based microheater is believed to be widely applicable to soft micro-electro-mechanical system(MEMS) heating devices.
Highlights
Recent years have seen great progress in employing microfluidic technology in the field of wearable electronics [1], physiological monitoring systems [2] and biochemical synthesis application [3]
As shown in Supplementary Video S1, the void continued to grow in the same direction rather than the opposite direction after the opposite voltage was applied and no obvious expansion of the PDMS microchannel was observed during the whole expansion
Because no obvious thermal expansion of the PDMS microchannel was observed and the expansion of EGaIn should be even smaller, the thermal expansion difference between the PDMS and EGaIn should not be the reason for the void growing in the video
Summary
Recent years have seen great progress in employing microfluidic technology in the field of wearable electronics [1], physiological monitoring systems [2] and biochemical synthesis application [3]. Our study focuses on a liquid metal-based soft microheater, whose heating element is fabricated by injecting the electrically conductive liquid metal into elastomeric microchannels. This work fabricates and optimizes a flexible microheater which adopts PDMS as its soft substrate and utilizes EGaIn-filled microchannels to produce Joule heat. Despite excellent mechanical softness and easy fabrication of the liquid metal-based microheaters, they are easy to break when the liquid-metal heating channels are subjected to high temperature. This breakage is caused by voids forming and expanding within the microchannels.
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