Chemical adhesion of a hydrogel on an elastomer surface enabling directionally-bendable actuators

Chemical adhesion is an effective protocol to enhance the interfacial strength of two different elements, which is of great significance in the design and fabrication of kinematics-controllable soft actuators. Based on a series of interfacial chemistry reactions, this work introduces hydrogel networks onto the surface of an elastomer film and enables the formation of an integral sandwich-like composite. The strong interfacial strength completely avoids the interfacial failure during actuating in response to external stimuli. The elastomer layer containing carbon nanotubes is capable of generating photothermal effects, endowing the sandwich-like composite with responsiveness to the irradiation of near infrared light. Upon exposure to humidity or immersion in water, the hydrogel composite absorbs water and swells to trigger the bending motion toward the elastomer side. The improved interfacial adhesion, together with the asymmetric physical structure, results in a sandwich-like composite with reversible and controlled kinematic motility in response to light and humidity/water. To examine it, various soft actuators such as a butterfly, flower, gripper and robot are prepared. All of them exhibit controlled and reversible motility when driven by near infrared light and humidity, where no interfacial failure takes place. The results demonstrate the promising potential for application in sensing and actuating systems.