Professor Hu Yanlei from the University of Science and Technology of China, Nat Commun Preparation of Durable Janus Thin Films with Mode Switching by Femtosecond Laser

Janus film is widely used in fields such as oil-water separation, water mist collection, and wearable patches due to its unique transmembrane directional water transport function. The function of traditional Janus thin films comes from the thickness direction of microchannels and single-sided chemical coating modifications (single-sided hydrophilic and hydrophobic modification of hydrophobic and hydrophilic substrates respectively). Water can be transported directionally from hydrophobic to hydrophilic surfaces through microchannels. However, during use, the chemical coating is prone to wear and tear, leading to functional failure. In non working conditions, microchannels are easily blocked by pollutants in the air, which greatly shortens the service life of Janus films. Faced with increasingly urgent practical application needs, the durability issue of Janus thin films urgently needs to be solved.

Professor Hu Yanlei from the School of Engineering Science at the University of Science and Technology of China and Associate Professor Zhang Yachao from Hefei University of Technology have innovatively considered the working mode and protection mode of Janus thin films separately. By stretching and releasing soft materials, they have achieved exposed and hidden protection of hydrophilic microporous groove channels, that is, switching between working and protection modes. When the Janus film encounters external mechanical friction or impact, the durability of the Janus film is improved by actively switching to the release protection mode. Based on the "mode switching" strategy, the team used femtosecond laser micro nano manufacturing method to prepare durable Janus thin films.

Research has found that the protective mode endows Janus film with mechanical durability, and it can still maintain the unidirectional transmission function of water droplets after 2000 friction cycles and 10 days of exposure to air (Figure 1). In addition, the protection mode can withstand harsh tests such as sandpaper friction, finger pressing, sand impact, tape peeling, and prevent pollutant particles from blocking channels (Figure 2). As a proof of concept, apply the mode switching durable Janus film to water mist collection in desert environments. For example, in the early morning when water mist is diffuse and there is no wind or sand, the Janus membrane is stretched to the working mode for water mist collection, and when a sandstorm occurs, it switches to a protective state to resist sand friction and impact. Taking the 30 minute water mist collection volume as an example, the results showed that the collection volume only decreased by 10% after rigorous testing, demonstrating the durable water mist collection ability of Janus film. In addition, long-term storage experiments were conducted on the protective mode Janus film under different temperatures, humidity, and chemical environments. The results showed that the water mist collection ability of the Janus film stored for 10 days was basically consistent with the original film, demonstrating the thermal stability, humidity stability, and chemical stability of the Janus film (Figure 3). The mode switching strategy proposed in this study has significant potential in promoting the practical application of Janus thin film functional devices in various fields such as multiphase separation purification, microfluidic control, and wearable health monitoring patches.

On February 16, 2024, the work was titled "Dual Janus membrane with on-demand mode switching fabricated by femtosecond laser" and published in Nature Communications.

Figure 1. Design and preparation of durable Janus film with "mode switching"

Figure 2. Mechanical durability test of Janus membrane under extreme conditions

Figure 3. Application of water mist collection based on durable Janus film

Source: Sohu