Transient Dual-Response Iontronic Strain Sensor Based on Gelatin and Cellulose Nanocrystals Eutectogel Nanocomposites

The emergence of wearable strain sensors in soft electronics has the potential to revolutionize healthcare and robotics. However, current sensors are based on petroleum-based conductive composites that have a limited strain range. Ionic conductors such as hydrogels offer expanded strain range but have poor long-term stability and restricted temperature operating window. Deep eutectic solvents (DESs) are promising nonaqueous electrolytes alternatives with green credentials. By combining DES electrolytes with biopolymers, transient ionic conductors are developed with high stretchability, and excellent chemical and thermal stability. Herein, cellulose nanocrystals (CNC) are incorporated, bearing OSO3H or COOH groups, to gelatin-based eutectogels to produce nanocomposites with enhanced properties and additional functionalities. The eutectogel nanocomposite containing 1.0 wt.% COOH-CNC demonstrate enhanced stretchability (375%) and ionic conductivity (3.0 mS cm-1) compared to the pristine gelatin-based eutectogel (300% strain and 2.0 mS cm-1, respectively). Moreover, the spontaneous assembly of CNC within the eutectogel results in birefringence, which changes when stretching the nanocomposites. Thus, CNC incorporation provides the gelatin-based eutectogel with a dual-response capabilities when stretched, expanding their applications to new areas such as transient multi-responsive strain sensors for wearable electronics, and multifunctional substrates for soft robotics, without compromising overall performance or sustainability. In this research, a dual-response nanocomposite is introduced, exhibiting simultaneous shear-induced changes in birefringence and resistivity. This dual response is enabled by the incorporation of carboxylated cellulose nanocrystals into a gelatin-based eutectogel containing a nonaqueous ethylene glycol-choline chloride deep eutectic solvent.image