Capillary-Based Microfluidic Fabrication of Liquid Metal Microspheres toward Functional Microelectrodes and Photothermal Medium

Abstract

Liquid metals (LMs) possess tremendous potential applications in flexible electronic devices, heat flow management, and smart actuators. Splitting the bulk LMs into microspheres is of great significance to fabricate free-standing and microscale LM-based functional materials and devices. However, it is difficult to disperse the bulk LMs into microspheres because of their large surface tension and high density. In this work, the capillary-based microfluidic chip is employed to continuously and automatically generate LM microspheres in a large scale. The capillary-based microfluidic fabrication is universally applicable in ionic aqueous solution, hydrophobic solution, and the polymeric aqueous solution. The precise size control of LM microspheres can be easily realized by the co-flowing configuration in the microchannels. The coefficient of size variation of monodispersed LM microspheres can be controlled to as low as 0.47%. The free-standing LM microspheres can be used as functional microelectrodes within a wide temperature range from −19.8 to 20 °C and to fabricate tunable integrated circuits with different output powers. Most importantly, the LM microspheres exhibit photothermal property, which is used to make the optical sensor with linear response and to conduct the solar energy harvesting. The capillary-based microfluidic fabrication of LM microspheres provides a facile and templated methodology for processing bulk LMs into microscale units. The LM microspheres with excellent electrical conductivity and photothermal property hold great promise for the development of miniature soft electronics, light-driven actuators, and energy conversion medium.

Liquid Metal Droplet and Graphene Co‐Fillers for Electrically Conductive Flexible Composites

“…The XRD patterns in Figure a depict that all samples contain peaks of crystalline α‐Ga and tetragonal In . Similar to the XRD pattern of the as‐sonicated EGaIn particles (Figure S4, Supporting Information), no oxide peaks of Ga and In are identified, which confirms the successful suppression of surface oxidation of the EGaIn droplets inside the composite using our two‐step method . An amorphous band between 30° and 40° is also observed in the diffractogram due to the molten gallium .…”

Liquid Metal–Based Soft Microfluidics

“…Microfluidics, which integrate functional fluids onto a chip‐like system with compact size and low energy consumption in a portable manner, show tremendous prospects in the field of drug/cell screening, sensing, health monitoring and microfabrication . Replacement of the traditional fluids by LM results in additional features to the system and shifts the applications away from biorelated fields to electronics and related fields . LM shows some unique advantages in LM‐based microfluidics.…”

“…[7] Replacement of the traditional fluids by LM results in additional features to the system and shifts the applications away from biorelated fields to electronics and related fields. [8][9][10][11] LM shows some unique advantages in LM-based microfluidics. First, LM can maintain electrical continuity while the system undergoes significant deformations.…”

Advances in Liquid Metal-Enabled Flexible and Wearable Sensors

“…There is a photo-thermal conversion in liquid metal microsphere, which is promising to not only liquid-metal optical sensors, but also light-driven actuators and as an energy conversion medium. Moreover, Zhang et al presented a flexible capacitive sensor based on liquid-metal microsphere as well [138]. It worked through the multi-plateau capacitance waveform when liquid metal sphere passed through the sensing area.…”

“…(E) Microscopy images showing liquid-metal microspheres produced by capillary-based microfluidics, reproduced with permission from [77]. (F) Schematic diagram of the photothermal conversion of liquid-metal microspheres and the near-infrared (NIR) sensor based on the liquid metal microsphere, reproduced with permission from [138].…”