Slippery magnetic track inducing droplet and bubble manipulation

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.

Photoelectric synergistic anisotropic slippery interface for directional droplets manipulation

Stimuli-responsive anisotropic slippery surfaces have displayed remarkable performance in directionally manipulating droplet transport behavior. However, most current reported anisotropic slippery materials have been limited to a single response mode, which often fails to satisfy the practical conditions of double or synergetic stimulation in complex environments. Here, an anisotropic photoelectric synergistic responsive paraffin-injected directional oxidized copper foam slippery interface (P/DOC3-S) with a low response threshold is reported. Owing to the fast photoelectric response of P/DOC3-S, the reversible control of the anisotropic sliding behavior of droplets is realized by remotely switching on and off the photoelectric field. Additionally, through optimizing the structure, the response voltage for P/DOC3-S can be reduced to 0.3 V under one sunlight. This work will provide insights into creating new types of smart slippery surfaces, which are potentially useful in microfluidics, directional liquid transportation, the semiconductor industry, and other related fields.

Controllable and Directional Transportation of Bubbles on Asymmetric Hexagonal Cage Substrate in Aqueous Environment

Controllable and directional bubble transport is usually the critical step in applications involving bubbles. However, current bubble transport strategies either are limited in controllability and transport distance or require the assistance of a specific external field. Here, we propose a strategy for bubble transport in an asymmetric hexagonal cage (ASHC), which works smoothly even under antibuoyancy conditions. The transport efficiency of bubbles can be greatly improved by adjusting the structural parameters of the cage. The control of the bubble depends only on the change of the bubble's volume, so there is no strict restriction on the driving force, which can be pressure, photothermal, electrothermal, and even acoustic-thermal forces. Moreover, we demonstrate that long-distance transport and controllable merging of bubbles can be easily achieved by cascading multistage ASHC structures. This investigation offers a simple, low-cost, extensible, and versatile construction for bubble transport for fundamental research and practical applications.