Dual thermo-responsive multifunctional ionic conductive hydrogel by salt modulation strategy for multilevel encryption and visual monitoring

Despite the current progress in thermo-responsive materials, it is still a significant challenge to develop superior multiple temperature-sensitive ionic conductive hydrogels with programmable regulation capability for interactive wearable iontronics. Here, a dual thermo-responsive ionic conductive hydrogel (DTICH) is constructed based on a salt modulation strategy, which cleverly integrates low-temperature sensitive sodium dodecyl sulfate (SDS) and high-temperature sensitive poly(N-isopropylacrylamide) PNIPAm-based polymer. Owing to the common ion effect and salting-out effect, the resultant DTICH hydrogel visually presents wide and tunable dual temperature response behaviors of 0-18℃ (Tk) and 37-80℃ (LCST) by controlling NaCl concentration for the first time. Meanwhile, benefiting from the synergy of NaCl and thermo-sensitive materials, the hydrogel is concurrently endowed with excellent stretchability (>900 %), adhesion (adhesion strength >30 kPa), frost resisting (-40℃) and multilevel encryption functions. More importantly, the DTICH hydrogel can ingeniously perceive mechanical force and external temperature via the changes of relative resistance and transparency, which can be applied as human–computer interfaces to interactively monitor human motions and temperatures in real time. Therefore, our study establishes a brand new and effective route for the rational design and fabrication of high-level visual interactive devices and smart wearable iontronics.