Water Sliding Angle Research Articles

Facile Fabrication of a Superhydrophobic Surface with Robust Micro-/Nanoscale Hierarchical Structures on Titanium Substrate.

A superhydrophobic surface with robust structures on a metallic surface could improve its application in various harsh conditions. Herein, we developed a new strategy to fabricate robust micro-/nanoscale hierarchical structures with electrical discharge machining and electrochemical etching on a titanium substrate. After modification by fluorinated silane, the static water contact angle and slide angle of the surface could reach 162 ± 2° and 4 ± 1°, respectively. The superhydrophobic surfaces showed good corrosion resistance and mechanical stability after scratching with sandpapers. In addition, the superhydrophobic surfaces had good self-cleaning performance even in an acidic environment as well as the potential to be used as guiding tracks in droplet microfluidics and lab-on-a-chip systems. These results are expected to be helpful in designing the surface of liquid float gyroscope parts.

Effective Harmful Organism Management I: Fabrication of Facile and Robust Superhydrophobic Coating on Fabric

Advances in harmful organism management are highly demanding due to the toxicity of conventional coating approaches. Exploiting biomimetic superhydrophobicity could be a promising alternative on account of its cost-effectiveness and eco-friendliness. Here, we introduce a facile method to fabricate a robust superhydrophobic coating on a fabric substrate. This is achieved by sequentially spraying TiO2-epoxy resin nanocomposite material and fluorocarbon-silane modified SiO2 nanoparticles (FC-silane SiO2 NPs). The superhydrophobicity is attributed to the nanoparticles constituting a micro/nano hierarchical structure and the fluorocarbon of the modified SiO2 NPs lowering the surface energy. The epoxy resin embedded in the coating layer plays an important role in improving the robustness. The robustness of the superhydrophobic surface is demonstrated by measuring the water slide angle of surfaces that are subject to salty water at 500 rpm stirring condition for up to 13 days. This study focuses on ensuring the superhydrophobicity and robustness of the coating surface, which is preliminary work for the practical management of macrofoulers. Based on this work, we will perform practical harmful organism management in seawater as a second research subject.

Three-dimensional Cu-Ni composite superamphiphobic surface via electrodeposition and fluorosilane modification

A superamphiphobic (SAP) surface was fabricated by electrodepositing Cu-Ni micro-nano particles on aluminum substrate and modifying via 1H,1H,2H,2H-perfluorodecyltrimethoxysilane. Scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy were employed to investigate the morphology and chemical composition. The results showed that the SAP surface had three-dimensional micro-nano structures and exhibited a maximum water contact angle of 160.0°, oil contact angle of 151.6°, a minimum water slide angle of 0° and oil slide angle of 9°. The mechanical strength and chemical stability of the SAP surface were tested further. The experimental results showed that the SAP surface presented excellent resistance to wear, prominent acid-resistance and alkali-resistance, self-cleaning and anti-fouling properties.

Fabrication of superhydrophobic Eucalyptus wood surface with self-cleaning performance in air and oil environment and high durability

In this study, a simple and cost-effective method was developed to fabricate superhydrophobic coating on wood surface. The prepared superhydrophobic coating had a large water contact angle (159°), less water slide angle (6°), good durability, abrasion resistance property, excellent thermal stability, and good acid and alkali resistance property. Notably, the coatings had self-cleaning properties in air or oil environment. The superhydrophobic coating was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy. We prepared the classical micro/nanostructured SiO2 on the wood surface on which the low surface free energy substance 1H,1H,2H,2H-perfluoroalkyltrichlorosilane (PFDS) was successfully modified. Furthermore, the treated wood had significantly better physical properties including water uptake and dimensional stability. The developed superhydrophobic coating is easy to fabricate and has great significance for the functional modification of wood.

Fabrication of superhydrophobic concrete used in marine environment with anti-corrosion and stable mechanical properties

Concrete is one of the wide used building materials in both marine engineering and architecture field. The first step of concrete structure deterioration is that corrosive medium invades into concrete. In this paper, a non-toxic fabricating method of superhydrophobic concrete with anti-corrosion and stable mechanical properties was proposed. Copper mesh and stearic acid were used to obtain the hierarchical micro-nano structure and low surface energy. The results indicate that the water contact angle and water slide angle of fabricated superhydrophobic concrete reached 159° and 5°, respectively. In addition, even after 60 s of mechanical polishing, the water contact angle was still greater than 150°. Moreover, compared with ordinary concrete, the anti-corrosion of fabricated superhydrophobic concrete was greatly improved. The fabricated environment-friendly superhydrophobic concrete with anti-corrosion and stable mechanical properties has important potential application value in the marine engineering.

Superhydrophobic Methylated Silica Sol for Effective Oil-Water Separation.

Superhydrophobic methylated silica with a core–shell structure was successfully fabricated by a sol-gel process. First, a pristine silica gel with an average particle size of ca. 110 nm was prepared, using tetraethylorthosilicate (TEOS) as a precursor, ethanol as a solvent, and NH4OH as a catalyst. Then, the superhydrophobic methylated silica sol was prepared by introducing methyltrimethoxysilane (MTMS), to graft the surface of the pristine silica gel with methyl groups. The structure and morphology of the methylated silica sol were characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), and transmission electron microscope (TEM). The characterization results showed that methyl groups were successfully grafted onto the surface of the pristine silica, and the diameter of the methylated silica was increased by 5–10 nm. Various superhydrophobic surfaces on glass, polyethylene terephthalate (PET) fabric, cotton, open-cell polyurethane (PU) foam, and polypropylene (PP) filter cloth were successfully constructed by coating the above substrates with the methylated silica sol and reached with a maximum static water contact angle and slide angle of 161° and 3°, respectively. In particular, the superhydrophobic PP filter cloth exhibited promising application in oil–water separation. The separation efficiency of different oil–water mixtures was higher than 96% and could be repeated at least 15 times.

Investigation of Effects of Acid, Alkali, and Salt Solutions on Fluorinated Superhydrophobic Surfaces

Extensive studies have been carried out to investigate the stability of superhydrophobic surfaces under acid, alkali, and salt solutions. It is noted that previous literature studies just demonstrated a variety of experimental phenomena. However, very few works have focused on the protection mechanism or failure mechanism of fluorinated superhydrophobic surfaces from the perspective of chemical aspects. Herein, this paper aims to investigate the effects of acid, alkali, and salt solutions on the stability of fluorinated superhydrophobic surfaces, and the anticorrosion/corrosion mechanism will be further proposed. The superhydrophobic coating was obtained on silicon substrates by laser surface texturing followed by fluoroalkyl silane modification. The resultant surfaces presented a water contact angle (WCA) of 157.6 ± 0.4° with a small water sliding angle (WSA) of 1.3 ± 0.3°. The newly fabricated superhydrophobic surfaces were then immersed in different concentrations of corrosive solutions (acid, alkali, and salt solutions). The revolution of surface wettability and surface morphology on treated silicon surfaces was evaluated through WCAs, scanning electron microscopy, and white light confocal microscopy. The results indicate that the hydrogen ions (H+) played a positive role in the retention of superhydrophobicity. However, the hydroxyl (OH-) and chloride ions (Cl-) presented the negative influence. The protection mechanism or corrosion mechanism under different solutions was proposed based on the X-ray photoelectron spectroscopy results. In addition, the potentiodynamic polarization and electrochemical impedance spectroscopy measurements provided strong support in data and were conducted to verify the rationality of the proposed mechanism.

Oil-Infused Silicone Prevents Zebra Mussel Adhesion

The remarkable underwater adhesion capacity of the invasive freshwater mussel species Dreissena polymorpha (zebra mussel) causes extensive damage each year. The adhesive interface between the substrate surface and the mussels' adhesive plaques plays a key role in zebra mussel biofouling. Silicone-oil-infused polydimethylsiloxane (iPDMS), an omniphobic material in the class of liquid-infused slippery surfaces, has been shown to develop a uniform, microscale, antifouling surface oil layer, which we hypothesized would be effective against zebra mussel fouling. iPDMS substrates with varying levels of oil saturation were tested for their ability to disrupt mussel adhesion by characterizing zebra mussel reattachment in a simulated freshwater environment for 3 days. On fully saturated iPDMS samples or those near full saturation, zebra mussels showed no reattachment, compared to 41% reattachment on PDMS controls (no oil infusion). For lower saturation levels, the frequency of reattachment was decreased relative to PDMS controls. Mussel detachment forces decreased in iPDMS as compared to PDMS, and adhesive failures occurred more frequently with higher iPDMS saturations. Surface analysis of the subsaturated iPDMS substrates showed incomplete coverage of the surface oil layer. After 3 days of immersion in artificial freshwater, subsaturated iPDMS substrates showed a decrease in slipperiness (measured by water slide angle), whereas in fully saturated iPDMS, the slipperiness was unchanged, despite no observed oil loss in either group. The decrease in slipperiness is attributed to microfouling of the subsaturated substrates, consistent with incomplete surface oil layer coverage, and supports the notion that full oil layer coverage is required for effective antifouling properties. Employing iPDMS as an antifouling coating shows promise against freshwater mussel adhesion, and this work further aids in understanding the antifouling mechanism of iPDMS and the role of the plaque-substrate interface in freshwater mussel adhesion.

Environmentally-friendly fabrication of a recyclable oil-water separation material using copper mesh for immiscible oil/water mixtures

Oily wastewater created by industrial disposal and oil spill disasters enormously affects human health and ecological systems. Environmentally-friendly methods for oil–water separation are highly desirable. We propose an environmentally-friendly approach for fabricating superwettable surfaces with recyclability to separate oil-water mixtures efficiently. A superwettable surface with a dendrite-like hierarchical structure for separating various oil–water mixtures was fabricated using copper mesh via modification by non-toxic stearic acid. The prepared surface was confirmed to be superhydrophobic and superoleophilic, in which the water contact angle, water slide angle and oil contact angle are 158°, 3° and 1°, respectively. These properties resulted in the surface achieving oil–water separation driven by gravity, and exhibiting efficient separation (> 98%) and high recyclability (throughout 22 consecutive cycles) of various oil–water mixtures. Moreover, the prepared surface also exhibited self-cleaning performance and stability to long-term water jet exposure. This efficient and environmentally-friendly method provides a green strategy for separating various oils from water.

A stearic acidified-ZnO/methyl polysiloxane/PDMS superhydrophobic coating with good mechanical durability and physical repairability

A robust stearic acidified-ZnO (SA-ZnO)/methyl polysiloxane/polydimethylsiloxane (PDMS) superhydrophobic coating had been fabricated on glass slide by a simple droplet-coating method. The obtained coating showed good superhydrophobicity with a water contact angle (WCA) above 150° and a water sliding angle (WSA) less than 2°. The surface morphology, roughness and components of the coating were analyzed by SEM, 3 D optical profiler and FT-IR, respectively. The SA-ZnO/methyl polysiloxane/PDMS superhydrophobic coating not only displayed good mechanical durability against sandpaper abrasion test and knife-scratch test, but also exhibited physical repairability to recover its superhydrophobicity after being exposed to some extreme conditions such as strong acid and alkali. This physical repair process could be repeated for many times until the coating was worn out. The coating also could maintain its superhydrophobicity under high-intensity UV irradiation and low/high temperature. The SA-ZnO/methyl polysiloxane/PDMS coating could be applied onto other substrates, including filter paper, cotton fabric and aluminium sheet.

Phragmites Communis Leaves with Anisotropy, Superhydrophobicity and Self-Cleaning Effect and Biomimetic Polydimethylsiloxane (PDMS) Replicas

Phragmites communis leaf (PCL) is anisotropic, superhydrophobic and shows a self-cleaning effect. The water contact angle (WCA) values along the vertical and parallel vein directions on PCL are 153° ± 2° and 148° ± 2°, respectively. In contrast, the water sliding angle (WSA) values along the vertical and parallel vein directions for PCL are 12° ± 2° and 7° ± 2°, respectively. The epidermal wax makes the leaves intrinsically hydrophobic. The microstructure of the PCL surface shows sub-millimetre-, micron- and nanometre-scale structures. The sub-millimetre ridge structure is the main reason for the anisotropy of the leaves. The micron-scale papillae structure has a strong hydrophobic enhancement effect, and the nanoscale sheet structure is the key factor in achieving a stable Cassie state, as well as superhydrophobicity and self-cleaning activities. PCL-like polydimethylsiloxane (PDMS) samples fabricated by template transfer technology exhibited the sub-millimetre ridge structure and micron-scale papillae from the natural PCL; they also show obvious anisotropy and strong hydrophobicity and have a certain self-cleaning effect. The WCA and WSA values along the vertical and parallel vein directions on PCL are 146° ± 2°, 23° ± 2°, 142° ± 2° and 19° ± 2°, respectively. The preparation of a biomimetic PCL surface has broad application prospects in micro-fluidic control and the non-destructive transmission of liquids.

Fabrication of durability superhydrophobic LDH coating on zinc sheet surface via NH4F-assisted in-situ growth and post-modification for enhancing anti-corrosion and anti-icing

In this work, a superhydrophobic layered double hydroxide (LDH) coating was fabricated on zinc sheet surface by in-situ growth and post-modification technology. The obtained zinc sheet exhibited excellent superhydrophobicity with a water contact angle (WCA) of 160° and a water sliding angle (WSA) of 5o. To determine the mechanical stability, chemical stability, storage stability of the superhydrophobic LDH coating on zinc surface, sandpaper abrasion test, tape-peeling test, immersion test and long-term exposure to the outdoors were employed. The results of stability test suggested that the LDH coating on zinc surface possessed excellent superhydrophobic stability (WCA > 150°, WSA < 10°) during all kinds of harsh conditions except pH = 1, indicating the superior adaptability to outdoor environment. More importantly, the superhydrophobic LDH coating on zinc surface exhibited excellent anti-corrosion efficiency (η = 99.99%) and delay icing ability (t = 75 min), which was beneficial to the application of zinc in a variety of practical fields.

Fabrication of multifunctional amphiphobic surfaces on copper substrates

Amphiphobic surfaces can protect metal from corrosion and pollution, while most methods of fabricating amphiphobic surfaces mainly focused on how to obtain specific rough structures by complex processes, particular equipments, tightly controlled conditions and long time modification with a low surface energy material, lacked of exploring how to obtain lower surface energy by improving low surface energy materials. Herein, a facile, easy to control, and time-saving modification method using an ingenious mixed modified solution of stearic acid and perfluorooctanoic acid was proposed to fabricate amphiphobic surfaces on copper substrates. The as-fabricated surface presented superhydrophobicity and oleophobicity with high oil contact angle (OCA) (136.6°), higher water contact angle (WCA) (156.7°) and fairly low water sliding angle (WSA) (close to 0°). In addition, superior stability was displayed by measuring the WCA in pH ranging from 1 to 13 and long-time water jet impact test. Furthermore, the amphiphobic surface possessed an excellent antifouling property even after being extracted from foul water contaminated with cement and some other common solutions. An outstanding anticorrosion property in 3.5 wt.% NaCl solution was also showed. The facile, easy to control, and time-saving method can provide insight into the fabrication of amphiphobic surfaces on metal substrates and can pave the way for various industrial and practical applications of amphiphobic surfaces.

Hybrid Nanosecond Laser Processing and Heat Treatment for Rapid Preparation of Super-Hydrophobic Copper Surface

The super-hydrophobic copper surface was obtained by using a nanosecond pulsed laser. Different micro- and nano-structures were fabricated by changing the laser scanning interval and scanning speed, before heating in an electric heater at 150 °C for two hours to explore the effect of laser parameters and heat treatment on the wettability of the copper surface. It was found that the laser-treated copper surface is super-hydrophilic, and then, after the heat treatment, the surface switches to hydrophobic or even super-hydrophobic. The best super-hydrophobic surface’s apparent contact angle (APCA) was 155.6°, and the water sliding angle (WSA) was 4°. Super-hydrophobic copper is corrosion-resistant, self-cleaning, and dust-proof, and can be widely used in various mechanical devices.

Transmittance and self-cleaning polymethylsiloxane coating with superhydrophobic surfaces

ABSTRACTA transmittance and self-cleaning polymethylsiloxane (PMS) coating with superhydrophobic surfaces was fabricated through an easy sol–gel method by using fluorine-free and available materials (methyltriethoxysilane). The PMS superhydrophobic surface was covered with low-surface-energy compounds, bestrewed with many micropores, had a water contact angle of 164 ± 1°, and had a water slide angle of <5°. The average transmittance of glass with PMS coating was 89.35% at 380–800 nm, which was close to the transmittance (90.09%) of bare glass. The coating was endowed higher transmittance (91.13%) after calcining at 500°C, it still retained its superhydrophobicity.

Double-function SiO2-DMS coating with antireflection and superhydrophobic surface

A double-function SiO2 coating with antireflection and superhydrophobic properties was fabricated through a cost-effective and time-efficient sol-gel method. Tetraethoxysilane was used as a precursor to obtain SiO2 with an antireflection property. Hexamethyldisilazane was used as a modifier to produce SiO2-DMS with a superhydrophobic behaviour. The SiO2-DMS coating had a water contact angle of 153° and a water slide angle of <10°. The optimised SiO2-DMS coating had an average transmittance of 96.07% at a wavelength of 300–800 nm. The entire process could be completed in a short time.

Preparation of Ag superhydrophobic surface on metal substrates

In this work, the facile approaches are developed for preparation the Ag superhydrophobic surfaces (SHSs) on zinc (Zn), copper (Cu) and aluminium (Al) substrates. The water contact angles (WCAs) of the Ag SHSs on Zn, Cu and Al substrates are 167°, 165° and 154°, respectively. Furthermore, the water sliding angle (WSA) of each surface is less than 1°. The morphology and chemical composition of the samples are characterized using scanning electron microscopy (SEM) and X-ray diffraction pattern (XRD). The as-prepared three kinds of SHSs possess the self-cleaning performance, which can quickly take the chalk away when the water droplets fall down the SHSs. In addition, the superhydrophobicity of the SHSs can well maintain after exposure to the air for 6 months, indicating that the surfaces can sustain good stability.

Polydimethylsiloxane-Based Superhydrophobic Surfaces on Steel Substrate: Fabrication, Reversibly Extreme Wettability and Oil-Water Separation.

Functional surfaces for reversibly switchable wettability and oil-water separation have attracted much interest with pushing forward an immense influence on fundamental research and industrial application in recent years. This article proposed a facile method to fabricate superhydrophobic surfaces on steel substrates via electroless replacement deposition of copper sulfate (CuSO4) and UV curing of vinyl-terminated polydimethylsiloxane (PDMS). PDMS-based superhydrophobic surfaces exhibited water contact angle (WCA) close to 160° and water sliding angle (WSA) lower than 5°, preserving outstanding chemical stability that maintained superhydrophobicity immersing in different aqueous solutions with pH values from 1 to 13 for 12 h. Interestingly, the superhydrophobic surface could dramatically switch to the superhydrophilic state under UV irradiation and then gradually recover to the highly hydrophobic state with WCA at 140° after dark storage. The underlying mechanism was also investigated by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Additionally, the PDMS-based steel mesh possessed high separation efficiency and excellent reusability in oil-water separation. Our studies provide a simple, fast, and economical fabrication method for wettability-transformable superhydrophobic surfaces and have the potential applications in microfluidics, the biomedical field, and oil spill cleanup.

Polyester hydrophobicity enhancement via UV-Ozone irradiation, chemical pre-treatment and fluorocarbon finishing combination

Abstract Enhancement in polyester substrates hydrophobicity was carried out by surface modification via chemical pre-treatment, UV-Ozone irradiation and fluorocarbon finishing combinations, which are referred to as CUF-process in this paper. Polyester fabrics were impregnated with different chemicals (Na 2 CO 3 , H 2 O 2 , H 2 O 2 /Na 2 SiO 3 , NaOH and CH 3 NH 2 ) before UV-Ozone gases exposure to investigate the effects of these precursor surface pre-impregnation on the effectiveness of UV-Ozone modification and final superhydrophobicity formation. The changes in substrate properties were by measuring 3 M water repellency (Water/Alcohol Drop Test), water sliding angle (WSA), water contact angle (WCA), wash and abrasion fastness, air permeability, tensile strength and visual appearance of treated fiber surfaces via SEM. The results indicated the usefulness of UV-Ozone treatment for creating proper surface roughness to improve the hydrophobicity of polyester fabrics after fluorocarbon finishing, especially when the fabric was pre-treated with NaOH and H 2 O 2 solutions. The lowest WSA value of 7.9° and the highest WCA of 142.2° were achieved on polyester fabrics using pre-treatment with 60 g/l NaOH and 42 ml/l H 2 O 2 CUF-treatments. Also, the obtained highest water repellency levels and the best air permeability properties led to significant increase in the substrate hydrophobicity did not show any adverse effect on tensile properties and strength deterioration.

Facile and scalable preparation of highly wear-resistance superhydrophobic surface on wood substrates using silica nanoparticles modified by VTES

In this study, an efficient, facile method has been developed for fabricating superhydrophobic surfaces on wood substrates using silica nanoparticles modified by VTES. The as-prepared superhydrophobic wood surface had a water contact angle of 154° and water slide angle close to 0°. Simultaneously, this superhydrophobic wood showed highly durable and robust wear resistance when having undergone a long period of sandpaper abrasion or being scratched by a knife. Even under extreme conditions of boiling water, the superhydrophobicity of the as-prepared wood composite was preserved. Characterizations by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy showed that a typical and tough hierarchical micro/nanostructure was created on the wood substrate and vinyltriethoxysilane contributed to preventing the agglomeration of silica nanoparticles and serving as low-surface-free-energy substances. This superhydrophobic wood was easy to fabricate, mechanically resistant and exhibited long-term stability. Therefore, it is considered to be of significant importance in the industrial production of functional wood, especially for outdoor applications.