【Research Background】

Flexible, wearable strain sensors have received widespread attention due to their numerous applications in electronic skin, personalized medical monitoring, and human-computer interaction. At the same time, conductive hydrogels are widely studied as emerging materials for flexible wearable strain sensors due to their excellent electronic properties, adjustable mechanical properties, and significant biological properties. However, conductive hydrogels using pure water as the dispersion medium inevitably freeze below zero, thereby limiting the transmission of ions. Therefore, such hydrogels cannot maintain electrical conductivity or mechanical properties, which severely limits their practical application at low temperatures. Even at room temperature, these hydrogels inevitably lose moisture due to evaporation, which hinders long-term stability and durability. Therefore, it is very necessary to develop a conductive hydrogel flexible strain sensor with reliable antifreeze performance, long-lasting moisturizing performance and long-term stability.

In recent years, a variety of anti-freezing, non-drying organic hydrogels have been prepared by adding organic reagents such as EG, glycerin, etc. to the hydrogel. However, the conductivity of organic hydrogels is reduced due to the reduced water content, which limits their potential applications in the field of flexible, wearable soft strain sensors. In order to obtain better conductivity, conductive fillers (such as carbon nanotubes, graphene, and conductive polymers) are integrated into the elastic hydrogel matrix to make a representative conductive hydrogel sensor.

【Achievement Introduction】

In 2019, Professor Wan Pengbo of Beijing University of Chemical Technology and Professor Yu Guihua of the University of Texas at Austin published an article in the internationally renowned academic journal Advanced Functional Materials : Conductive MXene Nanocomposite Organohydrogel for Flexible, Healable, Low-Temperature Tolerant Strain Sensors The research paper reports the production of a flexible wearable strain sensor with anti-freezing, long-lasting moisture retention, self-healing ability, superior mechanical properties and sensing performance based on strain-sensitive MNOH, which is a simple solvent The replacement method was obtained from MNH. MNH was prepared on a conformal coating of conductive MXene nanosheet network using a hydrogel polymer network composed of polyacrylamide (PAAm) and polyvinyl alcohol (PVA). The prepared MNOH shows strong anti-freezing ability under extreme temperature (-40 ℃) and has long-lasting moisture retention (8 d). In addition, thanks to the dynamic crosslinking between PVA hydroxyl and tetrahydroxyborate ions and the supramolecular interaction between EG, PVA and MXene, MNOH has excellent self-repairing ability. In addition, MNOH can also be assembled into a wearable anti-freezing self-healing strain sensor that detects human activities in real time at very low temperatures (-40 ° C), with a wide strain range (up to 350% strain) and high sensing sensitivity (GF = 44.85) and other advantages. This design shows huge potential applications for artificial skin, soft robots, and human-machine interfaces at extremely low temperatures.

【Graphic introduction】

Figure 1. Manufacturing principle diagram and SEM characterization of conductive, antifreeze, self-healing MNOH.

Figure 2.  Low temperature resistance of MNOH .

Figure 3.  MNOH‘s long-lasting moisturizing properties.

Figure 4. Self-healing properties ofMNOH.

Figure 5. Strain performance of MNOH.

【Summary of this article】

    This article demonstrates the manufacture of freeze-proof, non-drying and self-healing strain sensors assembled with MNOH, where MNOH is prepared from MNH by simple solvent replacement. MNH is obtained by incorporating a conductive MXene network into a hydrogel polymer network. By immersing MNH in the EG solution to replace part of the solvent of the water molecules, MNOH can be obtained simply. The large number of hydrogen bonds formed between water molecules and EG molecules prevent the formation of ice crystal lattices and also hinder the evaporation of water. Therefore, MNOH remains unfrozen and flexible at low temperatures ( -40 ° C ), and exhibits stable and long-lasting moisture retention (8 d). In addition, the dynamic cross-linking between PVA and tetrahydroxyborate ions and the supramolecular interaction between EG, PVA and MXene give MNOH self-healing ability. In addition, a wearable strain sensor was made using MNOH, which can monitor human activities wirelessly, with significant sensitivity (GF = 44.85) and wide strain range (up to 350%). This research provides a novel antifreeze, self-healing and non-drying organic hydrogel strategy for the assembly of wearable electronic sensors. The wearable electronic sensor has reliable antifreeze performance, stable long-lasting moisture and self-healing capabilities. It is widely used in electronic skin, human-computer interaction, and personalized health monitoring.

Literature link:

https://dx.doi.org/10.1002/adfm.201904507.

Source: MXene Frontier