Preparation of PVA/GO/h-BN Janus Film with High Thermal Conductivity and Excellent Flexibility via a Density Deposition Self-assembly Method

Janus films with asymmetric physical/chemical properties have attracted considerable attention due to their promising applications in personal thermal management, electronic skins, sensors, actuators, etc. However, traditional methods for fabricating Janus films conventionally need the assistance of an interface or auxiliary equipment, which are usually complex and time-consuming. Herein, flexible poly(vinyl alcohol) (PVA)/graphene oxide (GO)/h-BN (recorded as PVA/GO/h-BN) Janus films with thermally, optically, and electrically anisotropic properties are fabricated by a simple density deposition self-assembly method, which just utilizes the density difference between GO and h-BN during water evaporation. Experimental results show that the two sides of the acquired Janus films have obvious asymmetric characteristics. In the original state of the PVA/GO/h-BN Janus films, the thermal conductivity of the GO side (10.06 W·m⁻¹·K⁻¹) is generally lower than that of the h-BN side (10.48 W·m⁻¹·K⁻¹). But after GO is reduced, the thermal conductivity of the rGO side reaches 12.17 W·m⁻¹·K⁻¹, surpassing that of the h-BN side. In addition, the relative reflectance of the h-BN side of Janus film is also significantly higher than that of the rGO side, and the surface resistance difference between the two sides is about 4 orders of magnitude. The prepared PVA/GO/h-BN Janus films show great application potential in human thermal management, light conversion switches, and electronic skins. This study provides a simple and versatile strategy for fabricating Janus films with multifunctional (such as thermal, optical, and electrical) anisotropies.