An asymmetric graphene oxide film for developing moisture actuators

Although Janus films of different compositions have been commonly utilized to develop moisture actuators due to the different capabilities of swelling in materials, a sole material with a distinct structural design is also able to provide moisture-actuation. In this study, we simply used graphene oxide (GO) to fabricate a sole GO film with an asymmetric structure which consisted of a wavy layer and a smooth layer. Due to the asymmetric structure and excellent hygroscopicity of the GO material, the asymmetric graphene oxide (AGO) film (2.5 x 0.5 cm(2)) was responsive to moisture and showed a maximum bending angle change of approximate to 1800 degrees as the relative humidity (RH) changed. Compared with other reports about moisture actuators, the AGO film exhibited a superior bending capability. Furthermore, we propose a novel mechanism for moisture actuation of the AGO film based on our detailed observations, and a wavy structure has been introduced for showing great potential in bending deformation. Finally, the AGO film was used as a grabber to grab a leaf and it exhibited good capability to twine around a plastic rod. This work provides a novel pathway for the development of moisture-responsive materials for potential applications in robotics, artificial muscles and switches.