Conductive MXene Nanocomposite Organohydrogel for Flexible, Healable, Low-Temperature Tolerant Strain Sensors

Researchers are of great interest because of the enormous potential of conductive hydrogels in areas such as wearable strain sensors, electronic skin and personalized medical monitoring. However, a general conductive hydrogel uses water as a dispersion medium, and inevitably freezes below zero, resulting in deterioration of electrical conductivity and mechanical properties. At the same time, the water in the hydrogel is inevitably reduced due to evaporation at room temperature, resulting in poor moisturizing properties.

[Introduction]

Professor Yu Guihua from the University of Texas at Austin and Professor Wan Pengbo from Beijing University of Chemical Technology (co-author) and others by immersing MXene nanocomposite hydrogel (MNH) in ethylene glycol (EG) solution, using B An antifreeze, self-healing and conductive MXene nanocomposite oil hydrogel (MNOH) was prepared by replacing the diol solution with a portion of the water molecules in the hydrogel. MNH is prepared by introducing conductive MXene nanosheets into a hydrogel. MNOH can not freeze at a low temperature of −40 °C, and it can be wet for 8 consecutive days, with excellent self-repairing ability and mechanical properties. Moreover, it can be assembled into a wearable strain sensor to monitor human physiological activity at a very low temperature with a relatively wide strain range (up to 350% strain) and a high strain factor (44.85). The above results were recently published on Adv. Funct. Mater.

[Graphic introduction]

figure 1.



a. Preparation of MNOH

b. SEM image of the stripped MXene nanosheet

c, d. SEM image of lyophilized MNH

figure 2.



a. Effect of different soaking time on MLOH antifreeze performance in EG

b. Mass change of EG (inset) in MNOH and MNOH corresponding to different soaking times

c. Low temperature resistance of MNOH and MNH

Figure 3. Long-lasting moisturizing properties of MNOH



a. Comparison of MNH and MNOH stored for 8 days in an environment of 20 ° C and 50% RH

b. Mass change of MNOH stored in 20 ° C, 50% RH environment after soaking for different time

Figure 4.



a. Self-repair behavior of MNOH, where i is the original state, Figure ii is the fully segmented state, Figure iii is the state of successful self-repair, and Figure iv is the state of successful self-repairing and stretching.

b. Change in resistance during MNOH self-repair process

c. A circuit consisting of MNOH and LED indicators, where i is the original state, Figure ii is the fully segmented state, Figure iii is the state of successful self-healing, and Figure (iv–vi) is Figure i, ii and Schematic diagram of iii

Figure 5.



a. Circuit composed of MNOH or MNH and LED indicator at low temperature

b. Relative resistance change of MNOH sensor under different strains

c. Relative resistance change of MNOH sensor under small strain

d. Relative resistance change of MNOH sensor under large strain

e. Change in relative resistance of the MNOH sensor stored in response to finger bending for 6 hours at a low temperature of -40 °C

f. Changes in relative resistance of the MNOH sensor stored in response to swallowing saliva for 6 hours at a low temperature of -40 °C

【summary】

The research team used ethylene glycol solution to replace some of the water molecules in MNH, prepared MNOH, and assembled a flexible, repairable and low temperature resistant strain sensor with MNOH. The large number of hydrogen bonds between the water molecules and the ethylene glycol molecules in the MNOH prevents the freezing of MNOH and the evaporation of water. Therefore, MNOH has flexibility at a low temperature of -40 ° C and has a stable room temperature moisture retention. In addition, dynamic chemical bonds and supramolecular interactions within MNOH confer self-healing ability on MNOH. The strain sensor wirelessly monitors human activity with a strain factor of 44.85 and a strain range of up to 350%. This work has potential application prospects in the fields of electronic skin, human-computer interaction and personalized medical monitoring.

Literature link: Conductive MXene Nanocomposite Organohydrogel for Flexible, Healable, Low-Temperature Tolerant Strain Sensors (Adv. Funct. Mater., 2019, DOI: 10.1002/adfm.201904507)

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