Controlled shape deformation of bilayer films with tough adhesion between nanocomposite hydrogels and polymer substrates.

Shape-shifting materials have received increasing attention owing to their promising applications in soft robotics, biomedical devices, actuators, morphing aircraft and so on. However, their practical applications are limited due to their weak mechanical strength, low interfacial adhesion and complex preparation method. In this paper, bilayer films were synthesized by in situ one-step forming soft and water-swellable nanocomposite hydrogels on the surface of the rigid and nonresponsive poly(ethylene terephthalate) (PET) film without any surface modification. The strong interfacial toughness between the hydrogel layer and the PET layer, the high swelling ability of the soft hydrogel layer, and the high strength of the rigid PET film endowed the bilayer film with excellent self-bending behaviour. The shape deformation of the bilayer films can be controlled by adjusting the geometry parameters of the bilayer film, such as the hydrogel thickness, the aspect ratio and the width of the bilayer film. Moreover, the bilayer film exhibited excellent reversible bidirectional self-bending behaviour. In addition, the mechanisms for driving the shape transformation were discussed. We believe this work will provide a promising and simple strategy to develop novel responsive materials with controlled shape deformation.