An Al-assisted GO/rGO Janus film: Fabrication and hygroscopic properties

In this paper, we present a novel method combining drop-casting GO dispersion with an Al-assisted partial reduction technique to fabricate a freestanding Janus GO/rGO film. The laminar structure of Janus film facilitates the diffusion pathway of water molecules efficiently. The asymmetrical oxygen content of the film promotes a significant gradient of moisture uptake in GO (hydrophilic) and rGO (hydrophobic) layers, resulting in a macroscopic deformation of the Janus film proportional to the change in relative humidity. The induced strain in the film changes the resistance of the rGO film, which systematically varies as a function of the strain amplitude or equivalently the change in relative humidity. In the range of relative humidity (5 to 100%), the resistance increases gradually with measurable change in response to a change in relative humidity (RH) as low as 1%, with the change being steeper at RH >85%. The results provide foundational knowledge for developing a relative humidity sensor with high sensitivity, excellent repeatability, and fast response-recovery without the complexity of the currently available interdigitated transducer-based humidity sensors.