With the rapid development of electronic technology and the continuous improvement of people's living standards, the demand for flexible electronic devices is increasing. Flexible electronic technology requires electronic devices to have many new characteristics such as flexibility, stretchability, and biocompatibility. Liquid metal (LM) perfectly combines the deformation ability of liquid with the conductivity of metal, and has good chemical stability and excellent biocompatibility. It is an ideal flexible circuit material. However, the surface tension of LM is extremely high (such as gallium indium alloy (of which 74.5 wt% Ga and 25.5 wt% In), 624 mN m-1), which is difficult to process and difficult to compound with other substrates, which greatly limits the flexibility of LM. Practical applications in electronics.
The biomimetic intelligent materials research group led by Li Zhaoxu, a researcher at the Qingdao Institute of Bioenergy and Process, Chinese Academy of Sciences, prepared LM micro-nano droplets coated with alginate microgels by ultrasonicating LM in an alginate solution. In the process of ultrasound, alginate can not only promote the reduction of particle size by coordination of carboxyl group with Ga3 +, but also chelate Ga3 + to form microgels, thereby inhibiting further release of Ga3 + and improving the biocompatibility of the material. The alginate microgel-coated LM dispersion not only increases colloidal stability and chemical stability, but also greatly increases its affinity with flexible substrates, and can be used in electronic inks. Although the circuit composed of micro-nano droplets is insulated due to the oxide shell, its conductivity can be restored by applying pressure (4.8 × 105 S m–1). Such circuits can be used in areas such as wearable microcircuits, electrothermal drivers, and electronic skins.
Due to the presence of an oxide layer or a stabilizer on the surface of LM micro-nano droplets, the circuits deposited with it need to be restored by applying pressure, laser, high temperature and other treatments. These post-processing technologies not only consume energy, but also have many limitations in their application. . The research group found through research that ultrasonic LM in aqueous dispersion of biomass nanofibers (Nanofibers, NFs) (such as cellulose NFs, chitin NFs, silk NFs, etc.) can obtain stable dispersed LM micro-nano droplets . The dispersion liquid is dried at normal temperature and pressure, and the LM micro-nano droplets can be sintered into a continuous liquid metal conductive film.
In-depth research shows that bio-based NFs may have three effects: First, bio-based NFs have rich hydrophilic groups (such as hydroxyl, carboxyl, etc.), which can be cross-linked with Ga3 + during ultrasound, reducing the Particle size and increase the colloidal stability of liquid metal droplets. Second, bio-based NFs can generate high capillary forces during evaporation, which can destroy the outer shell of the LM micro-nano droplets. Third, increase The large liquid metal layer's adhesion to the substrate makes it stable to glass, polyethylene terephthalate (PET), styrene-ethylene-butene-styrene block copolymer (Styrene -ethylene-butene-styrene block copolymer (SEBS), Polydimethylsiloxane (PDMS), greased paper and other materials. The thin film or coating material prepared based on evaporation sintering has flexibility, high reflectivity, scalable electrical conductivity (200% elongation), good electromagnetic shielding effect, biodegradability, and has super fast resistance to humidity, light and electricity. The stimulus responsiveness and other characteristics, the evaporation sintering method can be widely used in flexible electronics such as microcircuits, sensing, wearable devices and flexible robots.