Mechanically Robust, Time-Programmable, Janus Hydrogel Actuator, and the Insights into Its Driving Principles

Abstract

Poly(N-isopropylacrylamide) (PNIPAM)-based hydrogels are widely used in the preparation of Janus actuators due to their remarkable temperature-responsive properties. However, preparing PNIPAM-based hydrogel actuators with excellent mechanical properties, mass transfer ability, and programmable deformation, as well as gaining a profound and systematic understanding of their driving mechanisms, remains a challenge to date. To address these challenges, an efficient PNIPAM-hydroxypropylmethyl cellulose/polyacrylamide-Graphene oxide (PNIPAM-HPMC/PAM-GO) Janus hydrogel actuator with strong interfacial stability was constructed based on the self-generation method; PNIPAM-HPMC was used as the active layer, and PAM-GO was used as the passive layer. The introduction of HPMC makes the active layer have excellent tensile strength (7.55–28.3 kPa) and mass transfer ability (39.07–73.03%), thereby improving the deformation ability of the actuator (239–360°). It can still achieve a 360° deformation after being actuated repeatedly 5 times. The deformation dynamics of the Janus hydrogel actuator under thermal response conditions were quantitatively analyzed by real-time tracking of the response behavior, and the important role of mechanical moduli in the deformation process of the Janus hydrogel actuator was revealed for the first time. Therein, the effect of the elastic modulus difference on the deformation of the actuator is 48 times that of the compression modulus difference. Finally, the Janus hydrogel actuator with high interface stability, mechanical robustness, time-programmable, and double-layer integration prepared in this work shows potential application in the fields of bionics, intelligent switches, and display systems.