Multipleresponsive Hydrogel with a Janus Structure: Fabrication, Characterization, and Application in Soft Actuator and Sensor Engineering

Polymer hydrogels have advantages in actuator/sensor engineering because of their various responses to environmental stimuli. However, the reported complicated synthetic routes and high-cost of monomers used limit their large-scale utilization in related areas. In this study, a Janus hydrogel composed of temperature-responsive poly (N-isopropyl acrylamide) (PNIPAM) and pH-responsive poly (sodium acrylate) (PSA) was fabricated from inexpensive monomers using a facile synthesis route. Owing to the asymmetric swelling behavior originating from the specific polymer in each layer and the porous structures in different media and at different temperatures, the Janus hydrogel exhibited excellent advantages in actuator/sensor engineering. Thus, these hydrogels have potential applications in the gripping and releasing of objects in toxic media as well as cryptography and can be used in an alarm system to monitor the safety of chemical production and the temperature of flammable and explosive solvents. In addition, the features of the Janus hydrogels incorporated with carbon nanotubes, such as the high sensitivity, large stretchability, and rapid and linear response, enabled their application as strain sensors for wearable technologies in the recognition of body movement and health detection.