Conformal ZnO nanocomposite coatings on micro-patterned surfaces for superhydrophobicity

A conformal coating process is presented to transform surfaces with inherent micro-morphology into superhydrophobic surfaces with hierarchical surface structure using wet chemical spray casting. Nanocomposite coatings composed of zinc oxide nanoparticles and organosilane quaternary nitrogen compound are dispersed in solution for application. The coating is applied to a micro-patterned polydimethylsiloxane substrate with a regular array of cylindrical microposts as well as a surface with random micro-structure for the purpose of demonstrating improved non-wettability and a superhydrophobic state for water droplets. Coating surface morphology is investigated with an environmental scanning electron microscope and surface wettability performance is characterized by static and dynamic contact angle measurements.     

Addressable Protein Patterning via Switchable Superhydrophobic Microarrays

We report on a simple process to create a switchable superhydrophobic surface where the water contact angle can be switched from a superhydrophobic state (ca. 167°) to a completely wetted state (< 10°). In the superhydrophobic state, the switchable superhydrophobic surface was resistant to the adsorption of proteins. However, once converted to a wetted state, the same surface promoted protein adsorption. We have developed a novel multicomponent protein‐patterning technique based on this unique property of the switchable superhydrophobic surface. It is demonstrated that up to 100 × 100 protein spots can be created within one second. Each element on the switchable superhydrophobic microarray can be addressed individually and different types of biomolecules can be selectively deposited on the microarray without losing their activity. When integrated with microfluidic channels, the switchable superhydrophobic surface allows the parallel patterning of protein molecules to be carried out without cross contamination.     

Effect of plasma pretreatment on durability of sol-gel superhydrophobic coatings on laser modified stainless steel substrates

Superhydrophobic surfaces were generated on stainless steel SS 304 substrates, using a combination of physical as well as chemical modification of the surface and tested for use in biomedical applications. Nanosecond pulsed laser was used for physical modification, i.e. creating nanoscaled roughness on the substrates. An additional chemical modification was performed using fluorosilane-based sol-gel nanocomposite coatings to further improve the hydrophobicity. Presently, the key challenge that such surfaces face, is to possess a substantial durability. In this study, a surface activation technique such as plasma pre-treatment was adopted to improve the adhesion of coatings on the laser treated substrates. The coatings deposited using dip coating technique were cured at 150 °C. The surface morphology and the roughness of the processed substrates and the coated samples were characterized using Atomic Force Microscope and Scanning Electron Microscope. The wettability of the surface was monitored and evaluated throughout the study using water contact angle measurements. Weathering tests and scratch resistance measurements using a crockmeter were carried out to evaluate the durability, which revealed that the adhesion could be improved with plasma treatment of the laser textured substrates, prior to coating deposition. Maximum anti-bacterial activity of up to 90% towards the bacterial species Escherichia coli was found on the substrates coated with the fluorosilane-based superhydrophobic coatings for an exposure time of 30 min, without any addition of external anti-bacterial agents. Thus, the preliminary results obtained from the present investigation were found to be promising and were indicative of use of these surfaces for biomedical applications.     

Superhydrophobic Pt–Pd/Al2O3 catalyst coating for hydrogen mitigation system of nuclear power plant

Passive auto-catalytic recombiner (PAR) system is an important hydrogen mitigation method which has been applied in most modern light water nuclear reactors. The two challenges for the highly efficient PAR are the detrimental effect of water and poisoning by fission products. In this study, to address the two challenges, superhydrophobic Pt–Pd/Al₂O₃ catalyst coatings were prepared by wet impregnation method and the grafting of 1H,1H,2H,2H-perfluorooctyltriethoxysilane.The formation of a Pt–Pd intermetallic compound was confirmed by in situ diffuse reflectance infrared Fourier transform infrared spectroscopy for the Pt–Pd/Al₂O₃ catalyst. The Pt–Pd/Al₂O₃ catalyst exhibited a superior resistance of water poisoning to the monometallic catalysts. In addition, compared with the monometallic catalysts, the least influence by the iodine poisoning was observed for the Pt–Pd/Al₂O₃ catalyst, which is attributed to the smallest influence on the bindings of H₂ and O₂ on the Pt–Pd intermetallic compound by the iodine addition. For the reactor with the superhydrophobic Pt–Pd/Al₂O₃ catalyst coating, under the conditions simulating the nuclear accident, the reaction was ignited immediately as soon as the hydrogen was introduced at 298 K and the hydrogen conversion kept 100% when the reaction temperature exceeded 398 K. The superhydrophobic Pt–Pd/Al₂O₃ catalyst coating showed great potential for the mitigation of hydrogen containing various poisons during the nuclear accident.     

Modification of the wettability of polymer surfaces using nanoparticles

The effects of nanoparticles, embedded into the matrices of polymer films, on the wettabilities of the surfaces of the composite films are investigated following a two-fold procedure. First, five particles such as silica (of two sizes), tin oxide, alumina and zinc oxide ranged from 7 to 100 nm are mixed with a poly(methyl siloxane). Second, silica nanoparticles (7 nm) are embedded in five different polymers such as poly(methyl methacrylate), polystyrene and three poly (alkyl siloxane) products. Nanocomposite films are produced by adding nanoparticles in the polymer solutions which are then sprayed on silicon substrates.     

A review on challenges,recent progress and applications of silica nanoparticles based superhydrophobic coatings

Over the past few decades, the study of superhydrophobic coatings (SHCs) gained the significant interest of worldwide researchers due to their tremendous applications in various sectors including, the metal industry, membrane industry, automation, structures, marine, defense, and medicines. The literature is full of review papers on the basics of SHCs, their synthesis methods, and their applications. But, minimal reviews are available on silica nanoparticles-based SHCs. However, silica nanoparticles are well-known material for SHCs due to their abundance, economical, transparency and ease of surface modification by various surface-functionalizing agents compared to other nanomaterials. Furthermore, silica nanoparticles are the most preferred material for the generation of nano-level roughness in the coatings to exhibit superhydrophobicity. Therefore, there is a great need to work in this direction. This work is dedicated to the challenges, recent progress and applications of silica nanoparticles-based superhydrophobic coatings.     

Fabrication of superhydrophobic self-cleaning manganese dioxide coatings on Mg alloys inspired by lotus flower

Superhydrophobicity is evolutionarily adaptive to surrounding environment. Lotus flower is naturally occurring superhydrophobicity. Artificial self-cleaning materials function effectively on superhydrophobic surfaces so that water droplets bead up and roll off the surface taking the contamination particles away. Inspired by lotus flower, we have fabricated superhydrophobic Mg alloy surfaces using manganese dioxide (MnO₂) microspheres encased in stearic acid shells. The prepared superhydrophobic Mg alloy surface provides exceptional self-cleaning ability in air and oil, and remains non-wetting even after dynamic water shear, or exposure to strong acid, strong base, and saline solutions as well as organic solvents showing excellent mechanochemical durability, with broad application prospect.     

Simultaneously spray-assisted assembling reversible superwetting coatings for oil–water separation

Here, superhydrophobic cuprous oxide(Cu_2O) with hierarchical micro/nanosized structures was synthesized via spray-assisted layer by layer assembling. The as-prepared superhydrophobic meshes with high contact angle(159.6°) and low sliding angle(1°) are covered with Cu_2O ‘‘coral reef"-like micro/nanosized structures. Interestingly, the superhydrophobic mesh surfaces became superhydrophilic again due to the oxidization of Cu_2O to CuO by annealing at a higher temperature(300 ℃). And the superhydrophobic properties would be recovered by heating at 120 ℃. Furthermore, the superwetting meshes were applied to design a miniature device to separate light or heavy oil from the water–oil mixtures with excellent separation efficiency. These superwetting surfaces by simultaneously spray-assisted layer by layer assembling technique show the potential application in universal oil–water separation.     

Prediction of sessile drop evaporation considering surface wettability

Previous studies suggest that most theoretical models for drop evaporation based on an ideally simplified domain in which evaporation occurs do not correlate well with experimental results. The present paper proposes a novel empirical model f(θ) as a simple function of the contact angle θ, which is to be used to predict temporal evolution of a sessile water drop volume when the drop evaporates on surfaces of various wettabilities widely adopted in microelectronic engineering. For hydrophilic and hydrophobic surfaces, the evolution of the drop volume during the evaporation process can be predicted more accurately by representing f(θ) as an empirical linear function rather than by using previous theoretical models. Furthermore, the proposed model can account for the increased evaporation rate on smooth surfaces, thus providing a wide applicability to various substrate surfaces. For cases involving a superhydrophobic surface, f(θ) can be represented by an empirical constant because the contact angle remains constant during evaporation, which is in excellent agreement with the experimental observation.     

Enhancement of superhydrophobicity and conductivity of carbon nanofibers-coated glass fabrics

This paper explores the role of carbon nanofibers (CNFs) on its potential to produce surperhydrophobic and conductive surfaces of glass fiber (GF) fabrics when processed by the catalytic chemical vapor deposition. Large-area helical CNFs were prepared over GF surfaces by the pyrolysis of acetylene. CNFs/GFs composites were characterized by XPS, SEM, and contact angle measurements. The results indicate the CNFs/GF fabrics surface exhibited excellent superhydrophocity and electroconductivity due to the grown CNFs The contact angle and volume resistivity of CNFs decorating the GF fabrics was equal to 152° and 1.13 × 10⁻³ Ω cm, respectively.