Salvinia-Effect-Inspired Magneto-Responsive Superhydrophobic Surfaces with Cluster-Distributed Microcilia Array

Inspired by the "Salvinia effect", a novel method for fabricating a magneto-responsive superhydrophobic surface coated with a cluster-distributed cilia array (CC-MRSS) was reported. This surface features a magnetically self-assembled nonuniform microcilia array and demonstrates exceptional microdroplet hydrophobicity, magnetic-responsive wettability, and corrosion resistance. The fabrication process involved mixing polydimethylsiloxane (PDMS) and carbonyl iron powders (CIPs), followed by dividing the mixture into two parts. The first part was poured into a 3D-printed female mold to form an elastic substrate with a hemispherical array. The second part was sprayed onto the substrate by using the air spray method. When an external magnetic field was applied during curing, a dense microcilia array self-assembled on the hemispheres of the substrate. As a result, the CC-MRSS, with a two-level composite microstructure, was successfully prepared. Contact angle tests showed a static contact angle of 157.0° for an 8 μL water droplet. Multiple samples were tested for controllable hydrophobicity by varying the spraying volume and CIP weight fraction. The relationship between wettability and the external magnetic field was analyzed, and a magneto-elastic coupling theory was developed to explain the contact angle variation. An optimal parameter scheme was proposed to achieve the maximum magneto-responsive contact angle range. The optimized CC-MRSS can switch between a low-hydrophobic state (118.2°) and a superhydrophobic state (151.5°) upon magnetic field switching, with high repeatability over ten cycles. Notably, the Salvinia-inspired CC-MRSS maintains an air film underwater, just like the Salvinia leaf, reducing surface-solution contact and offering superior corrosion resistance over other magnetic ciliary array surface materials.

Superwettable Nanomaterials: Fabrication, Application, and Environmental Impact

The increasing global concerns over energy consumption, environmental pollution, and sustainable development have sparked intensive research interest in advanced surface engineering solutions. This perspective critically reviews the development of superwettable surfaces as promising candidates for addressing these challenges. We analyze three key architectures that enable different levels of liquid repellency: micro/nano hierarchical structures for superhydrophobicity, re-entrant features for superoleophobicity, and doubly re-entrant designs for superomniphobicity. Recent developments have demonstrated significant progress in creating more environmentally conscious surfaces, including fluorine-free superhydrophobic textiles that reduce water and energy consumption in maintenance, energy-efficient smart windows with switchable wettability for building temperature regulation, and marine protective coatings that minimize chemical pollution. These advances contribute to environmental sustainability through multiple pathways: reduced resource consumption, improved energy efficiency, and decreased chemical pollution. However, challenges remain in achieving long-term durability, cost-effective fabrication, and comprehensive understanding of environmental impacts. This perspective provides insight into the current state of the field while highlighting the critical balance between performance optimization and environmental considerations in the development of next-generation superwettable materials.

Organic Matter Transfer Caused by Concentration Difference Creates TC4 Surfaces with Switchable Wettability

In this paper, low-cost electrochemical processing and heat treatment were adopted to fabricate titanium alloy surfaces with switchable wettability. Meanwhile, surface structure, roughness, and oxide content were regulated by electrochemical processing voltage. The effects of surface structure, roughness, oxide content, temperature, and time of heat treatment on switchable wettability were investigated. In addition to suitable structural conditions, surface chemistry is also crucial to preparing metal surfaces with switchable wettability. The surface chemistry of electrochemical processed surfaces was changed by organic matter transfer during heat treatment. In a certain voltage range, suitable surface structure, high roughness, and surface oxide content by high voltage contribute to the organic matter transfer. In a certain range of heating temperature and time, the concentration difference of organic matter is the premise of organic matter transfer. Concurrently, the higher the temperature, the faster the speed of organic matter transfer. Different from other relevant studies, the hypothesis that the concentration difference promotes organic matter transfer is proposed and verified by interesting experiments. The difference concentration of organic matter between the environment and the samples, as well as between the two samples, was created to promote organic matter transfer. Therefore, the electrochemical processed surfaces with switchable wettability were obtained by organic matter transfer in two ways.

Arylazopyrazole-Modified Thiolactone Acrylate Copolymer Brushes for Tuneable and Photoresponsive Wettability of Glass Surfaces

Photoswitches have long been employed in coatings for surfaces and substrates to harness light as a versatile stimulus to induce responsive behavior. We previously demonstrated the viability of arylazopyrazole (AAP) as a photoswitch in self-assembled monolayers (SAMs) on silicon and glass surfaces for photoresponsive wetting applications. We now aim to transfer the excellent photophysical properties of AAPs to polymer brush coatings. Compared to SAMs, polymer brushes offer enhanced stability and an increase of the thickness and density of the functional organic layer. In this work, we present thiolactone acrylate copolymer brushes which can be post-modified with AAP amines as well as hydrophobic acrylates, making use of the unique chemistry of the thiolactones. This strategy enables photoresponsive wetting with a tuneable range of contact angle change on glass substrates. We show the successful synthesis of thiolactone hydroxyethyl acrylate copolymer brushes by means of surface-initiated atom-transfer radical polymerization with the option to either prepare homogeneous brushes or to prepare micrometer-sized brush patterns by microcontact printing. The polymer brushes were analyzed by atomic force microscopy, time-of-flight secondary ion spectrometry, and X-ray photoelectron spectroscopy. Photoresponsive behavior imparted to the brushes by means of post-modification with AAP is monitored by UV/vis spectroscopy, and wetting behavior of homogeneous brushes is measured by static and dynamic contact angle measurements. The brushes show an average change in static contact angle of around 13° between E and Z isomer of the AAP photoswitch for at least five cycles, while the range of contact angle change can be fine-tuned between 53.5°/66.5° (E/Z) and 81.5°/94.8° (E/Z) by post-modification with hydrophobic acrylates.

Thermal and magnetic dual-responsive switchable device with superhydrophilicity/underwater superoleophobicity and excellent targeted oil–water separation performance

In view of the increasingly serious problem of oil–water separation, it is a convenient and practical method to introduce a hydrogel coating on the surface of materials to make super-wetting materials. Nowadays, researchers of super-wetting materials pay more attention to the research and development of responsive materials. Here, a thermal and magnetic dual-responsive superhydrophilicity/underwater superoleophobicity switchable device (Fe3O4@PNIPAM-Cu) was simply fabricated using the Fe3O4 nanoparticles, poly-N-isopropylacrylamide (PNIPAM) hydrogel as the functional coating and copper foam as the skeleton through a one-step solution immersion method. The separation efficiency of the benzene-water mixture of this dual-responsive device can reach up to 99.98%. Even after 10 separation cycles, it maintained an efficiency of more than 99.90%. At temperatures above ~34°C, the device can stop oil–water separation. The experiments presented here demonstrate this dual-responsive device possesses excellent superhydrophilicity/underwater superoleophobicity, thermal-responsive property and magnetic navigation function.

Intelligent Coatings with Controlled Wettability for Oil-Water Separation

Intelligent surfaces with controlled wettability have caught much attention in industrial oily wastewater treatment. In this study, a hygro-responsive superhydrophilic/underwater superoleophobic coating was fabricated by the liquid-phase deposition of SiO₂ grafted with perfluorooctanoic acid. The wettability of the surface could realize the transformation from superhydrophilicity/underwater superoleophobicity (SHI/USOB) to superhydrophobicity/superoleophilicity (SHB/SOI), both of which exhibited excellent separation performance towards different types of oil-water mixtures with the separation efficiency higher than 99%. Furthermore, the long-chain perfluoroakyl substances on the surface could be decomposed by mixing SiO₂ with TiO₂ nanoparticles under UV irradiation, which could reduce the pollution to human beings and environment. It is anticipated that the prepared coating with controlled wettability could provide a feasible solution for oil-water separation.

Biomimetic macroscopic hierarchical moire gratings

Large-scale hierarchical macroscopic moire gratings resembling the surface structure of Peruvian lily flower petals are fabricated on azobenzene molecular glass thin films using a Lloyd's mirror interferometer. It is shown that nanostructured linear and crossed moire gratings can be made with pitch values reaching a few millimeters. Also, using atomic force microscopy, scanning electron microscopy, optical microscopy, and surface profilometry techniques, it is shown that the obtained moire gratings have two-fold or three-fold hierarchical structures fabricated using a simple all optical technique.

Evolution of and Disparity among Biomimetic Superhydrophobic Surfaces with Gecko, Petal, and Lotus Effect

It is desirable to turn one kind of superhydrophobic (SHPO) surfaces into another by changing surface topography alone and attaining solid surfaces with tunable properties. Herein, gecko-, petal-, and lotus-like SHPO surfaces, composed of ZnO tetrapods and polydimethylsiloxane, are realized by adjusting the roughness factor and length scale of roughness, while keeping the surface chemistry the same. Afterward, water droplet sliding and impacting are investigated. The surfaces behave similarly in spreading but deviate from each other in sliding, receding, jetting, and rebounding due to their different adhesive properties. Moreover, the disparity between surfaces with petal and lotus effects is well explained by Furmidge's and Young-Dupre equations. On the other hand, these formulas fail to elucidate the surface with gecko effect because of its inside sealed air that produces negative pressure upon droplet motion. This paper provides a facile topography evolution path and a manifest correlation between topography and performance in water droplet dynamics for SHPO surfaces with gecko, petal, and lotus effects.