ENGINEERING TECHNOLOGY

New progress has been made in the research of multifunctional liquid metal hydrogels


Recently, the team of Tian Xingyou and Zhang Xian, Department of Polymer and Composite Materials Research, Institute of Solid Matter, Chinese Academy of Sciences, together with Associate Professor Yang Yanyu of Zhengzhou University, used gallium-indium alloy (EGaIn) to initiate polymerization and used as a flexible filler to construct a super-stretched, self-healing LM/PVA/P (AAm-co-SMA) dual-network hydrogel that can be used for human-computer interaction and infrared camouflage. The results were published in Materials Horizons.

A hydrogel is a soft material with a three-dimensional network structure, and conductive hydrogels can be obtained by introducing ions, conductive polymers, and conductive fillers. However, due to the inherent rigidity of the conductive polymer conjugated structure, the incompatibility of the conductive filler with the hydrogel matrix, and the salting out effect, the mechanical properties of most conductive hydrogels are poor, such as low toughness, low tensile strength, and unsatisfactory self-healing and self-healing properties, which greatly limits the application field of hydrogels.

As a liquid metal (LM) with a melting point close to or below room temperature, gallium indium alloy (EGaIn) can be prepared into EGaIn microspheres by ultrasonic dispersion for use as nanofillers. Unlike other rigid nanofillers, they can adapt to the deformation of the polymer matrix, effectively toughening the polymer. In addition, gallium (Ga) in EGaIn can initiate radical polymerization of vinyl monomers. Ga3+ can coordinate with carboxyl groups and hydroxyl groups to form dynamic sacrificial bonds for energy dissipation. Therefore, gallium-based liquid metals have the potential to improve the mechanical properties of polymer matrices.

In view of this, the researchers used gallium indium alloy (EGaIn) to initiate polymerization while acting as a flexible filler to construct a super-stretched and self-healing LM/PVA/P (AA-CO-SM) dual-network hydrogel. The synergy of rigid PVA microcrystalline network and tough P(AAm-co-SMA) hydrophobic network, as well as ion coordination and hydrogen bonding (multiple physical crosslinking) between polymer networks, confer excellent superstretchability (2000%), toughness (3.00 MJ/m3), notch resistance and self-healing (healing efficiency greater than 99% at room temperature 24 h). LM hydrogels exhibit sensitive strain sensing behavior and can be used for human-computer interaction for motion recognition and health monitoring. In addition, due to EGaIn’s good photothermal effect and low infrared emissivity, LM hydrogel shows great application potential in infrared camouflage.

Researcher Zhang Xian of Hefei Institute of Materials and Associate Professor Yang Yanyu of Zhengzhou University are co-corresponding authors of the paper, and Master student Li Xiaofei is the first author of the paper. The research work was supported by the National Natural Science Foundation of China and the President Fund of Hefei Institute of Materials. (Source: Hefei Institute of Physical Sciences, Chinese Academy of Sciences)

Related paper information:https://doi.org/10.1039/D3MH00341H

Figure 1. Characterization of mechanical properties of liquid metal hydrogels.

Figure 2. (a) Schematic diagram of the pressure sensor; (b, c) the change in resistance when “CAS” and “USTC” are written on the pressure sensor; (d) Schematic diagram of a human-computer interaction system; (e) The volunteer wearing the human-computer interaction glove opens his finger and the LED screen displays the number “5”; (f) Human-robot interaction gloves prepared by LM hydrogel display numbers based on the flexion of the volunteer’s fingers.

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