Cellulose nanocrystals boosted hydrophobically associated self-healable conductive hydrogels for the application of strain sensors and electronic devices

Currently, hydrogel-based flexible devices become hot areas for scientists in the field of electronic devices, artificial intelligence, human motion detection, and electronic skin. These devices show responses to external stimuli (mechanical signals) and convert them into electrical signals (resistance, current, and voltage). However, the applications of the hydrogel-based sensor are hampered due to low mechanical properties, high time response, low fatigue resistance, low self-healing nature, and low sensing range. Herein, a strain sensing conductive hydrogel constructed from the CNCs (cellulose nanocrystal) reinforced, in which acrylamide and butyl acrylate work as hydrophilic and hydrophobic monomers respectively. The incorporation of CNCs in the polymeric system has a direct effect on their mechanical properties. The hydrogel having a high amount of CNCs (C₄), its fracture stress and fracture strain reached 371.2 kPa and 2108 % respectively as well as self-healing of C₄ hydrogel Broke at 499 % strain and bore 197 kPa stress. The elastic behavior of the hydrogels was confirmed by the rheological parameter frequency sweep and strain amplitude. Besides this our designed hydrogel shows an excellent response to deformation with conductivity 420 mS m^-1, shows response to small strain (10 %) and large (400 %) strain, and has excellent anti-fatigue resistance with continuous stretching for 700 s at 300 % strain, with 140 msec response time, and gauge factor 7.4 at 750 % strain. The C₄ hydrogel can also work as electronic skin when it is applied to different joints like the finger, elbow, neck, etc. The prepared hydrogel can also work as an electronic pen when it is worn to a plastic pen cover.