Superhydrophobic Materials

This study aims to minimize the mechanical,
chemical and thermal damages on the blades of a compressor
used in aerospace engines by developing a superhydrophobic
coating on the blade surface. In the absence of
any information in open literature for the fabrication of
such coatings, an one-step plasma spray process was
implemented. For this, a well mixed powder of Ni and Ti
was used as feedstock material. The superhydrophobicity
characteristic of the coating was confirmed by the measurement
of the contact (165) and sliding angles (8 ± 1)
by the sessile drop technique. The adhesion test of the
coating showed the high force of adhesion at the interface
with a failure limit of 40.85 MPa. Furthermore, the abrasion
test depicted an excellent abrasion resistance of the
coating. These two investigations indicated that the coatings
had a very high mechanical durability. The coatings
also showed an excellent thermal stability up to 400 C.
Beyond this temperature (at 600 and 900 C), the superhydrophobic
characteristic changed for hydrophobic.
The pH and corrosion tests were also performed to assess
the chemical stability of coatings. They showed that the
coatings retained the superhydrophobic property for pH
ranging between 9.5 and 2.4. Beyond this range, at pH =
10 and pH = 2, the contact angles were 138 and 143,
respectively. In addition, the coatings exhibited a better
corrosion resistance than the substrate and coatings
developed by using other deposition techniques.

Research and development on superhydrophobic carbon nanostructures and their nanocomposites have high industrial significance. Here, a comprehensive review of the topic is provided. Reported works on superhydrophobic surfaces and coatings of carbon nanotubes, nanofibres, nanospheres/nanothorns/others, nanodiamond, fullerene and their various nanocomposites with metals, ceramics, and polymers are described. Superhydrophobic nanostructured carbon soot, graphitic carbon, and others are also presented. The section on superhydrophobic graphene is presented concisely at the end. Reports in different application areas, including anti-corrosion, anti-icing, oil separation, anti-biofouling, and sensors, are discussed separately. Superoleophobic and superamphiphobic surfaces are also discussed.

The economical and straightforward electrochemical methods
have attracted significant research attention as commercially
viable fabrication approaches for superhydrophobic surfaces, particularly
complex-shaped objects. The present review provides a
concise account of recent updates on different electrochemical
methods reported for fabricating superhydrophobic surfaces and
coatings. The methods discussed include electrodeposition, electropolymerization,
electrophoretic deposition, anodic oxidation,
micro-arc oxidation, electrochemical etching, and electrochemical
machining.

Reliable PDMS and aluminum NPS coating have been developed to protect the wood from deterioration and other water-absorbing materials in humid conditions. Thus, alumina that readily available was utilized to make a harsh surface, which afterward combined chemically with PDMS to develop the hydrophobic characteristics. A few substitute layers of PDMS together with alumina particles were established to ensure hydrophobic properties, and the water impact and emery paper tests were investigated. The glass substrates and other hydrophilic materials were used to apply the coating to limit its water absorption. The coated wood that developed super-hydrophobic properties was examined by dif erence and change in contact angle by analyzing the level of water absorption in covered and uncovered wood samples

Superhydrophobic coatings are projected as a practical approach to tackle the weak aqueous corrosion resistance of Mg/Mg alloys. The present review provides the most recent updates in this area. The various low surface energy treatments reported are presented first, followed by the methods employed for developing hierarchical surface micro/nanostructuring. Reported works in different application areas, including anti-corrosion, biomedical and anti-icing are systematically discussed. Concise descriptions of self-healing characteristics and long-term durability of the superhydrophobic surfaces provided. Reports on superamphiphobic surfaces also deliberated.

The development of corrosion resistant superhydrophobic thin films on aluminum surfaces has attracted great interest for industrial applications. In the present work, zirconium-based superhydrophobic thin films were fabricated on AA6061 aluminum alloy substrates by a simple electrode-position process. The thin film coated Al substrate exhibited excellent superhydrophobicity with a higher water contact angle of 162 ± 3˚com3˚com-pared to the hydrophilic as-received Al substrate with a contact angle of 83±2˚. The surface morphology of the fabricated thin films on Al sub-strate shows uniform micro-nano porous structures. The polarization resistance of the as-received Al and the zirconium-based superhydropho-bic thin films on the Al substrate are 23 kΩ.cm 2 and 788 kΩ.cm 2 , respectively. These results show excellent anti-corrosion property of zirconium-based superhydrophobic thin films to provide high corrosion protection for Al substrates.

Amongst vertebrates, the avian egg is unique in its structure and form. Bird eggs show a large range in shape, size and colour, the diversity of which has inspired much interest and debate. We have identified a new biological structure present in the surface of the eggshell, which is seemingly specific to one group of birds whose breeding ecology is unique within the avian kingdom. The guillemot group (Uria sp.) of the Alcidae family breed on exposed marine cliff faces, and with no nest used, the eggs are laid directly on the rock surface. The eggs are constantly exposed to sea-salt spray and guano from the incubating parents. The conical-like structural protrusions present in the eggshell surface of guillemot eggs are analogous with the nano-scale hierarchical arrangements identified in lotus leaves (Nelumbo sp.), the purpose of which is self cleaning. These structures are entirely absent in the eggs of 217 other birds species studied, including those nesting in similar environment...

Amongst vertebrates, the avian egg is unique in its structure and form.  Bird eggs show a large range in shape, size and colour, the diversity of which has inspired much interest and debate. We have identified a new biological structure present in the surface of the eggshell, which is seemingly specific to one group of birds whose breeding ecology is unique within the avian kingdom. The guillemot group (Uria sp.) of the Alcidae family breed on exposed marine cliff faces, and with no nest used, the eggs are laid directly on the rock surface.  The eggs are constantly exposed to sea-salt spray and guano from the incubating parents. The conical-like structural protrusions present in the eggshell surface of guillemot eggs are analogous with the nano-scale hierarchical arrangements identified in lotus leaves (Nelumbo sp.), the purpose of which is self cleaning. These structures are entirely absent in the eggs of 217 other birds species studied, including those nesting in similar environments, and those closely related to the guillemots from a phylogenetic perspective. Through comparative experiments we demonstrate how the guillemot eggshells exhibit hydrophobicity, have increased surface roughness and surface area, and a high rate of gas exchange under constant conditions. We conclude that these differences, a result of the conical protrusions in the eggshell surface, are an adaptation to the unusual breeding environment of the guillemot, in particular the salt and guana exposure.

Perfluorocarbon chains, that is, perfluoroethyl, CF3CF2−, perfluoro-n-propyl, CF3CF2CF2−, perfluoro-iso-propyl, (CF3)2CF−, and perfluoropolyether (PFPE) residues, were covalently bonded on the surface of a carbon black using perfluorodiacyl and PFPE peroxides. Thermal decomposition of the fluorinated peroxides allows the covalent linkage of fluorinated radicals to the polycyclic aromatic structure of the carbon black. Contact angle measurements in agreement with XPS data revealed a gradual enhancement of the water repellence with increasing fluorine content on the surface. When perfluoroalkyl chains were bonded to the carbon black the morphology and the surface areas of the modified carbonaceous materials were mostly retained as shown by BET and SEM analyses.

Superhydrophobic conductive carbon blacks were prepared by covalent bonding of perfluorocarbon and perfluoropolyether chains on the conductive carbon black surface. Perfluorodiacyl and perfluoropolyether peroxides were used as reagents for the chemical treatment. Their thermal decomposition produced respectively, perfluoroalkyl and perfluoropolyether radicals that directly bonded the polycyclic aromatic structure of carbon black surface. Measurements of contact angles with water on molded pellets made with carbon black powder demonstrated that water droplets were enduringly stable on the treated carbon blacks. Contact angle values were significantly high, exceeding the superhydrophobicity threshold. On the contrary, the droplets were adsorbed in few seconds by the native carbon black. Conductivity measurements showed that the covalent linkage of fluorinated chains weakly modified the electrical properties of the conductive carbon black, even if the surface properties changed so deeply. The relationship between the linkage of fluorinated chains and the variations of physical–chemical properties were studied combining electron spectroscopy, resistivity measurements, X-ray diffraction, scanning electron microscopy, surface area analysis and thermal gravimetric analysis. The superhydrophobic conductive carbon blacks were compared with a superhydrophobic carbon black obtained by direct fluorination of conductive carbon black with elemental fluorine, F2.