The University of Science and Technology of China (USTC) has learned on February 28 that a team of Professor Hu Yanlei and Associate Researcher Zhang Yachao from the Micro and Nano Engineering Laboratory of the School of Engineering Sciences at USTC has innovatively considered the working mode and protection mode of Janus films separately, and realized the protection of hydrophilic micropore-groove channels in both exposed and hidden modes, i.e., the switching of the working/protection modes, through the stretching and releasing of the soft materials. The research results were recently published in Nature Communications.
Janus films are widely used in oil-water separation, water-mist collection, and wearable patches with their unique transmembrane oriented water transport function. The functionality of traditional Janus films originates from microchannels in the thickness direction modified with a single-sided chemical coating, through which water can be transported directionally from the hydrophobic to the hydrophilic surface. However, the wear and tear of the chemical coating and the clogging of the microchannels by airborne pollutant particles in the off-peak state have greatly shortened the service life of Janus films. The durability of Janus films is an issue that needs to be addressed in order to meet the increasing demands of real-world applications.
Using femtosecond laser etching, the research team prepared three-dimensional microchannels consisting of lattice-like microgrooves and micropores on a pre-stretched silica substrate and modified the microgrooves with a hydrophilic coating, while the backside of the microgrooves maintained the intrinsic hydrophobicity of the silica gel to realize Janus functionality. After the release of the silicone, the micro-slots and micro-pores are closed to protect the hydrophilic coating inside the micro-channels against mechanical impacts. The on-demand switching of the stretching mode and the release protection mode gives the Janus film mechanical durability. The protection mode not only resists continuous mechanical friction, but also acts as a storage mode to slow down the failure of the hydrophilic coating, realizing the unidirectional water permeability function for a long period of time.
According to the researchers, the durability of the Janus film is improved by actively switching to the protection mode when the film encounters external mechanical friction or impact. Based on the "mode-switching" strategy, the research team utilized a femtosecond laser microfabrication method to prepare durable Janus films. It was found that the protective mode gave the Janus film mechanical durability, maintaining the unidirectional permeability of water droplets after 2,000 friction cycles and 10 days of exposure to air. In addition, the protection mode withstood harsh tests such as sandpaper rubbing, finger pressure, sand impact, and tape peeling.
The researchers say their proposed mode-switching strategy has significant potential for advancing the practical applications of Janus films in a variety of fields, including multiphase separation and purification, microfluidic manipulation, and wearable health-monitoring patches.
