Nature-Inspired Superhydrophobic Coating Materials: Drawing Inspiration from Nature for Enhanced Functionality.

Superhydrophobic surfaces, characterized by exceptional water repellency and self-cleaning properties, have gained significant attention for their diverse applications across industries. This review paper comprehensively explores the theoretical foundations, various fabrication methods, applications, and associated challenges of superhydrophobic surfaces. The theoretical section investigates the underlying principles, focusing on models such as Young's equation, Wenzel and Cassie-Baxter states, and the dynamics of wetting. Various fabrication methods are explored, ranging from microstructuring and nanostructuring techniques to advanced material coatings, shedding light on the evolution of surface engineering. The extensive applications of superhydrophobic surfaces, spanning from self-cleaning technologies to oil-water separation, are systematically discussed, emphasizing their potential contributions to diverse fields such as healthcare, energy, and environmental protection. Despite their promising attributes, superhydrophobic surfaces also face significant challenges, including durability and scalability issues, environmental concerns, and limitations in achieving multifunctionality, which are discussed in this paper. By providing a comprehensive overview of the current state of superhydrophobic research, this review aims to guide future investigations and inspire innovations in the development and utilization of these fascinating surfaces.

Water Purification by Green Synthesized Nanomaterials.

BACKGROUND: Water pollution is one of the important causes of human fatality in the world, particularly in underdeveloped or developing countries. Moreover, with rapid industrialization and urbanization, the problem of water pollution is posing a severe threat to health and livelihood. The pollutants found in water are of varied nature and depend on the source of the water. Several techniques have so far been adopted to purify contaminated water. All the techniques have one or the other disadvantages, limiting their applications on large scale, sustainability, and long-term usage. The advances in the field of nanoscience and technology have opened a new horizon for replacement/improvement of conventional ways with more efficient methods. Presently, green synthesized nanomaterials are being used for water purification. METHODS: Plant extracts and microbes are being used to synthesize nanomaterials, which are used as catalysts, adsorbents and membranes for water purification. RESULTS: Nanomaterial-based techniques could create problems for the environment due to various chemicals used in their production step, thus defeating the ultimate purpose. In this regard, green nanomaterials can prove to be extremely useful both in terms of sustainability and efficiency. CONCLUSION: This review illustrates various ways of how green nanomaterials can be utilized for water remediation and summarizes the recent work done in this emerging research area.

Rapid fabrication of a dual-scale micro-nanostructured superhydrophobic aluminum surface with delayed condensation and ice formation properties.

Aluminum (Al) is widely used in all forms of industry, including automobile, aerospace, transmission lines, and exchangers, and in general household appliances. Ice accumulation on Al surfaces may cause serious problems, especially during the winter, leading to critical damage to mechanical systems. In this study, we developed a superhydrophobic coating with anti-icing properties on an Al surface using a simple and cost-effective technique. The superhydrophobic dual-shape micro-/nanostructured (MN-) Al surface was fabricated by a facile chemical etching and an anodization method, followed by surface modification with polydimethylsiloxane (PDMS) via a simple thermal vapor deposition method. The static contact angle of the fabricated surface was more than 160 °C. Compared with the bare surface and the silicone oil-infused PDMS coating (SLIPS) on the MN-structured Al substrate, the fabricated superhydrophobic surface displayed excellent anti-icing. Ice formation on the superhydrophobic surface was delayed by 80 and 45 min at -5 °C and -10 °C, respectively, at a relative humidity of 80% ± 5%. The superhydrophobic surface demonstrated an increase of almost four and two times delay in icing time on the surface over bare and SLIPS surfaces, respectively. The coalescence induced jumping behavior of condensate water droplets was also investigated on the fabricated surfaces. The result indicates that the superhydrophobic surface can effectively delay ice/frost formation by the synergetic effect of surface morphology and the extremely low adhesive property of the surfaces, which allows the self-propelled jumping phenomenon at low temperature and high humidity. This proposed simple, fast, and cost-effective method could be applied to design large-scale anti-icing surfaces.

Tuning of structural, optical, and magnetic properties of ultrathin and thin ZnO nanowire arrays for nano device applications.

One-dimensional (1-D) ultrathin (15 nm) and thin (100 nm) aligned 1-D (0001) and (0001¯) oriented zinc oxide (ZnO) nanowire (NW) arrays were fabricated on copper substrates by one-step electrochemical deposition inside the pores of polycarbonate membranes. The aspect ratio dependence of the compressive stress because of the lattice mismatch between NW array/substrate interface and crystallite size variations is investigated. X-ray diffraction results show that the polycrystalline ZnO NWs have a wurtzite structure with a = 3.24 Å, c = 5.20 Å, and [002] elongation. HRTEM and SAED pattern confirmed the polycrystalline nature of ultrathin ZnO NWs and lattice spacing of 0.58 nm. The crystallite size and compressive stress in as-grown 15- and 100-nm wires are 12.8 nm and 0.2248 GPa and 22.8 nm and 0.1359 GPa, which changed to 16.1 nm and 1.0307 GPa and 47.5 nm and 1.1677 GPa after annealing at 873 K in ultrahigh vacuum (UHV), respectively. Micro-Raman spectroscopy showed that the increase in E2 (high) phonon frequency corresponds to much higher compressive stresses in ultrathin NW arrays. The minimum-maximum magnetization magnitude for the as-grown ultrathin and thin NW arrays are approximately 8.45 × 10-3 to 8.10 × 10-3 emu/g and approximately 2.22 × 10-7 to 2.190 × 10-7 emu/g, respectively. The magnetization in 15-nm NW arrays is about 4 orders of magnitude higher than that in the 100 nm arrays but can be reduced greatly by the UHV annealing. The origin of ultrathin and thin NW array ferromagnetism may be the exchange interactions between localized electron spin moments resulting from oxygen vacancies at the surfaces of ZnO NWs. The n-type conductivity of 15-nm NW array is higher by about a factor of 2 compared to that of the 100-nm ZnO NWs, and both can be greatly enhanced by UHV annealing. The ability to tune the stresses and the structural and relative occupancies of ZnO NWs in a wide range by annealing has important implications for the design of advanced photonic, electronic, and magneto-optic nano devices.

Mechanically robust superamphiphobic aluminum surface with nanopore-embedded microtexture.

A simple fabrication technique was developed for preparing a mechanically robust superamphiphobic surface on an aluminum (Al) plate. Dual geometric architectures with micro- and nanoscale structures were formed on the surface of the Al plate by a combination of simple chemical etching and anodization. This proposed methodology involves (1) fabrication of irregular microscale plateaus on the surface of the Al plate, (2) formation of nanopores, and (3) fluorination. Wettability measurements indicated that the fabricated Al surface became super-repellent toward a broad range of liquids with surface tension in the range 27.5-72 mN/m. By varying the anodization time, we measured and compared the effects of morphological change on the wettability. The adhesion property and mechanical durability of the fabricated superamphiphobic Al surface were evaluated by the Scotch tape and hardness tests, respectively. The results showed that the fabricated Al surface retained mechanical robustness because the down-directed surface made by nanopores on the microtextured surface was durable enough even after high force was applied. Almost no damage of the film was observed, and the surface still exhibited superamphiphobicity after the tests. The fabricated superamphiphobic surface also remained stable after long-term storage. The simple and time-saving fabrication technique can be extended to any large-area three-dimensional surface, making it potentially suitable for large-scale industrial fabrications of mechanically robust superamphiphobic surfaces.

Fabrication of amphiphobic surface by using titanium anodization for large-area three-dimensional substrates.

Superamphiphobic functional Ti foils were fabricated using anodization techniques. By varying the supply voltage and anodization time, a two-step anodization method was used to maximize the contact angle of water and various oils. The morphology of the TiO2 nanotube surface is important to achieve superamphiphobicitiy. The anodized surface maintained good superamphiphobic stability with long-term storage. Furthermore, the wettability properties toward both water and various oils can be easily and reversibly switched from hydrophobic and oleophobic to hydrophilic and oleophilic, respectively, and vice versa via air-plasma treatment and fluorination. The developed simple technique can be applied to any large-area three-dimensional surfaces to fabricate amphiphobic Ti surfaces.

PECVD based silicon oxynitride thin films for nano photonic on chip interconnects applications.

Thin silicon oxynitride (SiO(x)N(y)) films were deposited by low temperature (~300°C) plasma enhanced chemical vapour deposition (PECVD), using SiH(4), N(2)O, NH(3) precursor of the flow rate 25, 100, 30 sccm and subjected to the post deposition annealing (PDA) treatment at 400°C and 600°C for nano optical/photonics on chip interconnects applications. AFM result reveals the variation of roughness from 60.9 Å to 23.4 Å after PDA treatment with respect to the as-deposited films, favourable surface topography for integrated waveguide applications. A model of decrease in island height with the effect of PDA treatment is proposed in support of AFM results. Raman spectroscopy and FTIR measurements are performed in order to define the change in crystallite and chemical bonding of as-deposited as well as PDA treated samples. These outcomes endorsed to the densification of SiO(x)N(y) thin films, due to decrease in Si-N and Si-O bonds strain, as well the O-H, N-H bonds with in oxynitride network. The increase in refractive index and PL intensity of as deposited SiO(x)N(y) thin films to the PDA treated films at 400°C and 600°C are observed. The significant shift of PL spectra peak positions indicate the change in cluster size as the result of PDA treatment, which influence the optical properties of thin films. It might be due to out diffusion of hydrogen containing species from silicon oxynitride films after PDA treatment. In this way, the structural and optical, feasibility of SiO(x)N(y) films are demonstrated in order to obtain high quality thin films for nano optical/photonics on chip interconnects applications.