Bioinspired Fluoride-Free Magnetic Microcilia Arrays for Anti-Icing and Multidimensional Droplet Manipulation.

The accumulation of ice on surfaces will bring safety issues to various human activities. Researchers have been actively developing superhydrophobic surfaces (SHS) as good anti-icing materials. However, some limitations, such as high cost, complexity of preparation, and lack of sufficient durability in extreme environments, restrict their practical applications. Inspired by bronchial mucosa cilia structure and the superhydrophobic lotus leaf structure, we generated ordered magnetic microcilia arrays (MMA) surfaces within 1 min by a fast and controllable microhole assisted magnetic-induced microcilia self-growth method. Fluoride-free superhydrophobic MMA (SMMA) was prepared by impregnating MMA into hexadecyltrimethoxysilane (HDTMS) modified SiO2 solution. SMMA exhibits excellent static anti-icing performance, which can significantly delay the freezing of static droplets in supercooled environments. The SMMA surface still maintains excellent dynamic anti-icing performance at -30 °C after 100 times of supercooled droplet impact. Furthermore, SMMA shows anti-icing performance for up to 2 months at low temperatures (-18 °C). Due to the sensitive magnetic response and excellent bending properties of the cilia, the MMA and SMMA surfaces also demonstrate outstanding multifunctional droplet manipulation under a magnetic field. The MMA surface has the ability to vertically capture and release droplets. The SMMA can achieve horizontal transport of droplets, mixing and microchemical detection, antigravity droplet transport in an 8° inclined array, and even complex objects can be easily transported. More importantly, the SMMA surface exhibits outstanding mechanical durability and chemical stability. It provides insights into the preparation of integrated anti-icing and droplet manipulation surfaces by using a simple green and low-cost method.

Manipulation of bubble collapse patterns near the wall of an adherent gas layer.

This paper aims to apply experimental methods to investigate the effect of the thickness of gas layers on the wall on the collapse direction of spark-induced bubbles. In the experiment, two high-speed cameras synchronously record the time evolution of the bubbles and the corresponding parameters such as the normalized collapse position and bubble collapse time. Experiments yielded results for individual bubbles over a range of normalized distances from 0 to 4.0 for different air layer thicknesses. Based on the morphology of the bubbles, the experimental jets were visualized into six different modes, namely, forward jet (FJ), merging jet (MJ), bidirectional jet (BJ), reversing jet (RJ), forward followed by reversing jet (FRJ), and non-directional jet (NDJ). The height of the air layer on the wall is affected by the fluctuation of the bubble volume and shows the opposite trend to the change of the bubble volume. The air film reaches its maximum height when the bubble collapses, which affects the final jet pattern. In addition, as the thickness of the air layer increases, the center of the bubble gradually migrates away from the wall. The different collapse modes and the migration of the bubble centers have positive significance for reducing cavitation erosion in engineering.