A multi-responsive actuator with sensing capability based on poly (N-isopropyl acrylamide)/poly (sodium acrylate) Janus hydrogels

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. The asymmetric swelling between PNIPAM and PSA in different media and at different temperatures makes the Janus hydrogels have a multi-stimuli response, meanwhile, the interpenetrating layer between PNIPAM and PSA indicated a good interfacial adhesion for easy transfer of internal stress and deformation. Thus, the Janus hydrogels exhibited excellent advantages in actuator/sensor engineering, demonstrating the potential to grip and release objects in toxic media, encrypt, monitor and control safety in chemical production, and alert 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.