Multifunctional flexible polyvinyl alcohol nanocomposite hydrogel for stress and strain sensor

Recently, hydrogels have attracted considerable interests due to their intrinsic flexibility and adjustable mechanical properties. However, the integration of high conductivity, enhanced mechanical performance, and plasticity into one single hydrogel is still challenging. In this work, TEMPO-oxidized cellulose nanofibers (TOCNF, diameter 20–50 nm, length $$\ge$$ 1 um) are used as the efficient dispersant of multiwalled carbon nanotubes (MWCNTs, out diameter 5–15 nm, length 10–30 um). Conductive hydrogels are prepared through a simple one pot process and freeze–thaw cyclic method in combination with Fe3+ ions and TOCNF-MWCNT dispersions in polyvinyl alcohol (PVA) hydrogels. The resulting hydrogels demonstrate high water content (~ 88.8%), mechanical properties (ultimate stress of 1.1 MPa, strain of 336%), and conductivity (0.57 S/m), which can be applied to the preparation of stress or strain sensors. The hydrogel-based resistance sensor is applied to human motion detection, showing a sensitivity of 1.876 kPa−1 with pressure lower than 16 kPa. Similarly, the hydrogel-based capacitive sensor can detect imperceptible pressure of 20 Pa. In addition, the hydrogels also reveal excellent plasticity. In conclusion, the conductive hydrogel possesses excellent comprehensive properties, providing inspiration and potential for the preparation and application of wearable strain sensors.