Highly transparent superamphiphobic surfaces by elaborate microstructure regulation

Mechanistic Insight into the Synthesis and Morphological Evolution of Superhydrophobic Silica Nanotubes

Silica nanotubes have significant applications in various fields, including thermal insulation, self-cleaning, and catalysis. Currently, the synthesis methods of silica nanotubes are mostly limited to the template method. In this work, a template-free strategy and vapor-phase approach were used to prepare silica nanotubes. Poly(methylhydrosiloxane) (PMHS) was hydrolyzed and condensed in a high-temperature closed reactor by using ammonia as a catalyst. The resulting product was then subjected to template-free self-assembly to synthesize silica nanotubes incorporating methyl groups. The silica nanotubes were synthesized under varying conditions, resulting in lengths ranging from 50 nm to several micrometers, exterior diameters between 40 and 120 nm, and wall thicknesses varying from 7 to 30 nm. The synthesized products underwent morphology analysis using TEM and FESEM for morphology analysis, elemental composition analysis using XPS, and chemical structure identification using FTIR, and the possible formation mechanism of silica nanotubes formation was also speculated. Furthermore, the coatings formed by silica nanotubes exhibited remarkable superhydrophobic self-cleaning properties with a water contact angle of 162° and a rolling angle of less than 1°.

Facile Preparation of Robust Superamphiphobic Coatings on Complex Substrates via Nonsolvent-Induced Phase Separation

Superamphiphobic surfaces have great potential in many fields but often suffer from complicated, expensive, and time-consuming preparation methods, difficulty in applying them on complex substrates, and low stability. Herein, we show a facile fabrication of robust superamphiphobic coatings on complex substrates. A stock suspension was prepared by nonsolvent-induced phase separation of a silicone-modified polyurethane (Si-PU) adhesive containing fluorinated silica (FD-silica) nanoparticles. Then, superamphiphobic surfaces could be easily fabricated via dip coating in the suspension. The influences of phase separation and Si-PU/FD-silica ratio on the wettability and morphology of the coatings were studied. The coatings feature a microscale dense and nanoscale rough texture due to phase separation and rapid solvent evaporation, which enhances the stability by forming strong linkages among the nanoparticles while achieving high superamphiphobicity by trapping air stably in the nanopores. Consequently, the coatings show excellent static/dynamic superamphiphobicity, superior impalement resistance, and good mechanical, chemical, thermal, and UV aging stability. Additionally, the coatings have good anti-icing performance as demonstrated by the greatly extended water freezing time and weakened ice adhesion force in both simulated and real conditions.

Eco-Friendly Fabrication of Transparent Superhydrophobic Coating with Excellent Mechanical Robustness, Chemical Stability, and Long-Term Outdoor Durability

Surfaces that possess both superhydrophobicity and high transparency at the same time recently have attracted extensive attention in outdoor applications. However, fabrication and application of transparent superhydrophobic coating usually face following challenges: the micro-nano hierarchical structure required for superhydrophobicity usually leads to a decrease in the light transmittance due to its light trapping effect; fluorine-containing materials used in the preparation of superhydrophobic surfaces are potentially harmful to humans and the environment; and the superhydrophobic surface is easily destroyed by external factors. In this work, a transparent superhydrophobic coating was fabricated via an inexpensive and eco-friendly two-step method, that is, dipping glass substrate into the polydimethylsiloxane/SiO₂ suspension followed by calcination treatment. The prepared coating showed superhydrophobicity with a water contact angle of 164° and a sliding angle less than 1.0°. In the visible light region with the wavelength range of 300-900 nm, the maximal transmittance of the superhydrophobic coating was ∼91.4%, which is higher than that of the untreated glass substrate (∼90.9%). Moreover, the coating can maintain superhydrophobicity and high transmittance after sandpaper abrasion, water flow impact, immersion in strong acid/alkaline solution, UV irradiation, and long-term outdoor exposure. We believing that the coating has huge potential value in outdoor applications.

Robust Superhydrophobic and Repellent Coatings Based on Micro/Nano SiO2 and Fluorinated Epoxy

Superhydrophobic surfaces possess low mechanical strength, and can be easily contaminated by fluids with low surface tension, such as oil; this hinders their practical applications. In this study, fluorinated epoxy was prepared through the thiol-ene click reaction at first. The superhydrophobic surface with high oil-repellency was prepared by the addition of unmodified nano-SiO2 and micron-SiO2 to the fluorinated epoxy. The effect of the ratio of micro- and nano-silica particles on the morphology and wettability of the coating was investigated. It was shown that a re-entrant structure appears and FEP-S coating has good liquid repellency when the amounts of nano-SiO2 and micro-SiO2 are equal. The contact angles of the FEP-S coating (coating with the best liquid repellent performance) for water, glycerol, ethylene glycol, and diiodomethane were 158.6° ± 1.1°, 152.4° ± 0.9°, 153.4° ± 1.3°, and 140.7° ± 0.9°, respectively. In addition, the superhydrophobic coatings possess excellent mechanical and chemical durability, excellent performance in self-cleaning, corrosion resistance, and anti-icing properties. The preparation method of superhydrophobic coating is relatively simple; therefore, it has a wide range of applications and can also be applied to various substrates.

A Superhydrophobic and Oleophobic Silicone Sponge with Hierarchical Structures

The fabrication of amphiphobic materials requires a precise and complicated design, especially for 3D porous materials, and amphiphobic sponges have rarely been investigated. This paper describes the synthesis of a superhydrophobic and oleophobic silicone sponge (SS-F) by simply building hierarchical structures, that is, introducing a secondary structure on the pore walls of a hydrophobic and oleophilic silicone sponge. This simple and efficient synthesis method is based on the thiol-ene click reaction. The uniform structure, composition, and hierarchical structures of SS-F are confirmed. The results of the analyses show that the secondary microstructure improves liquid repellency, while the rough and porous surface design ensures durability. Thus, SS-F exhibits good stability, and the amphiphobicity of the surface could withstand scalpel cutting, cyclic compression, extreme temperatures of 250 and -196 °C for 5 h, and long-term storage in an ambient environment. Both its outer and inner surfaces show superhydrophobicity and oleophobicity, which restrict the ability of the adsorption of liquids, enabling its use in oil and water. The introduction of hierarchical structures paves a way for preparing other 3D porous materials.

Superamphiphobic coatings with antifouling and nonflammable properties using functionalized hydroxyapatite

Functional superamphiphobic coatings have attracted much attention due to their promising application prospects in oil transportation and anti-contamination, which call for the requirements of flame retardancy.

Coating of Silica Nanolayers on Carbon Nanofibers via the Precursor Accumulation Method

Surface modification of nanocarbons, for example, by coating with oxide nanolayers, is a research topic of significant interest because of the drastic changes in the physicochemical properties of the modified nanocarbons. One simple method of creating these oxide nanolayer coatings on nanocarbons is the precursor accumulation (PA) technique, which entails the following: (1) a precursor solution is added dropwise onto nanocarbon powder; (2) the solvent is dried, leaving the accumulated precursor on the nanocarbon surface; and (3) hydrolysis or decomposition of the precursor in air leads to the formation of oxide nanolayers on the nanocarbons. In this study, tetraethoxysilane (TEOS) was used as a precursor for coating silica nanolayers onto carbon nanofibers (CNFs). TEOS is so stable that it hardly undergoes hydrolysis on the surface of pristine CNFs. By treating CNFs with H₂SO₄/HNO₃, acidic functional groups were introduced onto the CNF surfaces. Silica nanolayers were successfully synthesized on these acid-treated CNFs via PA coating because the acidic functional groups catalyzed the hydrolysis of TEOS accumulated on the CNF surfaces. Scanning transmission electron microscopy indicated that the thickness of silica layer is approximately several nanometers. Pore size distribution analysis for the silica nanolayer suggested the presence of nanopores with 3-5 nm. The TEOS molecules could have accessed the functional groups through the nanopore; therefore, the number of silica nanolayers formed increased with the number of PA coatings. Finally, we compared the PA coating with conventional sol-gel and atomic layer deposition techniques.

A highly fluorinated SiO2 particle assembled, durable superhydrophobic and superoleophobic coating for both hard and soft materials

Solid surfaces with unique superhydrophobic and superoleophobic wettability in air have thus far shown incomparable applications in various fields. However, existing superoleophobic surfaces are always limited by their sophisticated fabrication strategies. Moreover, surface durability also restricts their further application since the well-designed structures and low-surface-energy chemical components are very susceptible to chemical and physical damage. In this study, we report the exploitation of a durable superhydrophobic and superoleophobic spray and dip coating, which is successfully fabricated by employing 3-aminopropyltriethoxysilane and fluoroalkyl silane to modify two sizes of SiO₂ particles. The wettability of the developed surface can be tuned by adjusting the mass ratio of the particles due to the change in hierarchical structure. On account of its super-repellence and independence from the substrate, the coating can be coated onto various hard and soft substrates. The as-prepared surfaces exhibit superphobicity to both water and organic fluids with low surface tension, and these liquid droplets can easily roll and bounce on the coated surface, leaving no residues. Furthermore, the coating shows positive antifouling and self-cleaning performances when contaminated or immersed in different liquids. Importantly, the coating is also durable, withstanding harsh environments, such as exposing the coated surface in acid and alkali solution or to high temperatures for a long time, without obviously altering its superamphiphobicity due to the high adhesiveness of poly(vinylidene fluoride hexafluoropropylene) and stable re-entrant-like structure. Its merits of a straightforward fabrication approach and multifunctionality may make the coating suitable for widespread practical applications.