Self-assembled ultrathin film of CNC/PVA–liquid metal composite as a multifunctional Janus material†
Ultrathin flexible Janus membranes with asymmetric structure and anisotropic conductive characteristics have attracted considerable attention due to their promising applications in soft electronics, microsensors, and energy management technologies. Conventional fabrication methods for Janus films usually require the assistance of interfacial or auxiliary equipment, which are usually complex and time-consuming. Herein, flexible and ultrathin liquid metal (LM) Janus films with integrated electrically, optically, and thermally anisotropic properties are presented for the first time. They were fabricated by the simple mixing of liquid metal nanoparticles with cellulose nanocrystal cotton and polyvinyl alcohol suspension, followed by self-assembly density deposition without the necessity of any interface or equipment, thereby making it easier and time-saving when compared with traditional interfacial or noninterfacial fabrication methods for Janus films. This unique substrate-ink-integrated nature of the liquid metal Janus film and shear-friction-enabled direct-writing technology provide a novel approach for the field manufacturing of customized electronics and one-step fabrication of multilayer circuits. It is particularly important to note that a microscale depth sensor can also be achieved in a simple manner; further, a smart acupuncture depth training model was developed by using liquid metal Janus films. In addition, the as-prepared Janus film could be used as a light conversion switch and temperature regulator. This study suggests a versatile strategy for creating Janus films with multifunctional (such as electrical, thermal, and optical) anisotropies.