Page 104 - Read Online

Huang et al. Soft Sci. 2025, 5, 24 https://dx.doi.org/10.20517/ss.2025.07 Page 11 of 19

High thermal effect of MXene and PA enables PCM organohydrogels to function as effective temperature
sensors for detecting thermal stimuli [Supplementary Figure 17]. The sensitivity of the thermal response is
quantified by the temperature coefficient of resistance (TCR). Relative resistance variation (ΔR/R , where ΔR
0
and R represent the resistance change and the original resistance, respectively) decreases significantly with
0
increasing temperature from -30 to 60 °C [Figure 4E], demonstrating a clear monotonic resistance-
[32]
temperature dependence and a typical negative resistance temperature coefficient characteristic .
Calculated TCR values are -43% and -2% °C in the temperature ranges of -30~10 and 10-60 °C,
-1
respectively, surpassing most reported temperature sensors [Figure 4F and Supplementary Table 5] [33-39] .
This exceptional thermal responsiveness is attributed to two main factors. Firstly, due to the narrow
bandgap semiconducting behavior of MXene nanosheets , thermal excitation during heating provides
[5]
electrons with enough energy to transition to higher energy states, increasing the carrier concentration. As a
result, MXene nanosheet’s conductivity increases with rising temperature, enhancing electron transport
efficiency. Secondly, migration rate of H ions, which are ionized from PA, accelerates with temperature,
+
enhancing the temperature-sensing ability of the PCM organohydrogel. Thus, the combination of electron
transitions and increased ion migration contributes to the superior temperature detection abilities of PCM
organohydrogels. Moreover, stable and repeatable temperature-sensing behavior was confirmed in five
cyclic tests, where the temperature was varied from 25 to -10, -20, and -30 °C [Figure 4G] and then from 25
to 40, 50 and 60 °C [Figure 4H], manifesting excellent reliability and electrical replicability of the PCM
organohydrogel as a temperature sensor. Notably, the temperature sensor can also detect consecutive
temperature variations, showcasing its practical applicability [Figure 4I]. For example, the temperature
sensor successfully distinguished the consecutive thermal flows produced by a hair dryer set to low,
medium, and high temperatures, illustrating the high sensitivity of the PCM organohydrogel temperature
sensor due to the temperature-induced changes in electron transport efficiency and ion migration rates.

Owing to excellent conductivity and mechanical robustness, the PCM organohydrogel is highly suitable as a
flexible strain sensor. Strain sensitivity is a crucial factor for evaluating the performance of strain sensors,
which is typically quantified by calculating the gauge factor (GF) from the slope of ΔR/R as a function of
0
the applied strain. As depicted in Figure 5A, the ΔR/R value increases with increasing the tensile strain and
0
can be split into three distinct linear sensing regimes: a low GF of 0.91 in the strain range of 0%-1,000%, a
medium GF of 1.67 in the range of 1,000%-2,300%, and an impressive GF of 3.24 in the range of 2,300%-
2,800%, demonstrating high sensitivity and wide strain sensing window. Notably, the PCM organohydrogel
exhibits an improved GF compared to the PC organohydrogel, indicating that the incorporation of MXene
significantly enhances the strain sensitivity of the sensor. Encouragingly, compared with the
organohydrogel without CS, the addition of CS in the organohydrogel system greatly improves the strain
response behavior of the flexible strain sensor [Supplementary Figure 18]. The strain-resistance
responsiveness of the PCM organohydrogel during the stretching process can be explained as follows:
firstly, a large number of evenly dispersed MXene nanosheets interconnect with each other in the PCM
organohydrogel matrix to form a complete conductive network framework for electron transport between
MXene nanosheets, while the porous microstructure facilitates the effective transmission of free ions,
endowing the PCM organohydrogel with favorable conductivity [Supplementary Figure 19A]. At small
strains, the spacing between adjacent MXene nanosheets increases due to their slippage, and the reduction
in the cross-sectional area of the hydrogel due to the Poisson effect decreases the transmission of free ions,
leading to an increase in resistance [Supplementary Figure 19B]. As the strain further increases, the MXene
nanosheets gradually separate from each other and the free ion conduction becomes slower, generating the
discontinuous conductive pathways in the PCM organohydrogel and a higher GF [Supplementary Figure
19C]. Figure 5B shows that the electrical signals of the PCM organohydrogel remain nearly identical when
stretched circularly at a 100% strain under applied stretching rates ranging from 50 to 400 mm·min ,
-1
demonstrating the typical rate-independent strain response feature, which is important for the rapid and