Low-Temperature Tensile Fatigue of a PVA/SA/CNT/CaCl ₂ Flexible Pressure Sensor

The flexible hydrogel-based sensor has gained much attention owing to chemical stability, high sensitivity, and ease of preparation. However, the low-temperature tensile fatigue of such a sensor is yet to be explored. Herein, we fabricate a flexible pressure sensor with antifreezing hydrogel developed by using poly(vinyl alcohol), sodium alginate, carbon nanotube, and CaCl2. The sensor exhibits a high sensing sensitivity (14.36 kPa–1) and fast response time (146 ms), which can be used to monitor various human activity signals. The sensitivity of the sensor remains about 88% after 10,000 stretching cycles at room temperature; however, it is attenuated to 17% at the same stretching condition at −40 °C. The 3D laser scanning microscopy observation shows that the crack growth rate is strongly temperature dependent. The finite element analysis and theoretical calculation results indicate that the disruption of dynamic hydrogen and ionic-bond networks and ice crystal formation is the key factors responsible for the fatigue failure of the sensor under low-temperature cyclic stretching. The presence of hydrogen/ionic bonds may provide sacrificial dynamic bonds that can break to dissipate the stress from mechanical deformation at room temperature. With the temperature decreasing, the disruption of ionic cross-links between the SA chains and Ca2+ increases the stress accumulation at the CNT/matrix interface, and the formation of rigid ice crystals within the PVA will generate additional stress concentration points, which accelerate PVA/CNT interfacial mismatch and ultimately lead to poor low-temperature fatigue performance of such sensors.