Superhydrophobic Surfaces Research Articles

A Fast and Green Method Based on Electroplating from Ethaline Electrolyte to Fabricate Superhydrophobic Surface for Corrosion Protection of Copper

A Fast and Green Method Based on Electroplating from Ethaline Electrolyte to Fabricate Superhydrophobic Surface for Corrosion Protection of Copper

Dust removal by water spray, condensation and defrosting based on superhydrophobic fin surface

Dust deposition on the fin surface of the outdoor heat exchanger seriously affects the operating efficiency of the air source heat pump (ASHP). Considering the operation characteristics of ASHP in summer for cooling and in winter for heating, a dust removal strategy is proposed based on superhydrophobic fin surface (SFS). In summer, the SFS is sprayed to remove dust by collecting the condensate water of air conditioning. In winter, by coupling the dust deposition with the condensation or frosting/defrosting phenomenon on SFS, the self-propelled motions of condensate droplets or the peeling off of the frost layer in defrosting is used to realize the dust removal. The experiment results show that the water spray on SFS has excellent dust removal performance, and the deposited dust is completely removed after 2 sprays. The dust is carried away by the jumping or gliding of the water droplets. The condensation has poor dust removal performance and takes long removal time. After several hours of condensation, the dust removal rate is 89.6 % and 40.0 % on SFS under different dust deposition levels. Due to the peeling off of the frost layer from the SFS at beginning of defrosting, the melting water at the bottom of the frost layer carries the dust away from the fin surface effortlessly. After 2 defrosting cycles, the dust removal rate reaches 99.6 %, while it is 50.1 % on the bare surface. Therefore, the strategy of dust removal by water spray in summer and defrosting in winter is suitable for ASHP.

Cost-effective, highly efficient, and stable evaporator constructed of Chinese ink impregnation superhydrophobic Xuan paper for solar-driven interfacial organic solvent purification

The lack of cost-effective, highly efficient, and stable photothermal conversion materials in organic solvents greatly hinders the development of solar-driven interfacial evaporation for organic solvent purification. Herein, inspired by the traditional Chinese calligraphy culture, black ink impregnated superhydrophobic Xuan paper membrane (XPBI) is fabricated via a pressing-impregnation method for solar-driven interfacial organic solvent purification. The high photothermal conversion efficiency and long-term stability of XPBI are attributed to the inherent stability, superhydrophobic surface, and abundant channels of Xuan paper, as well as strong adhesion with carbon black particles. As a result, XPBI exhibited a high light absorption of 94.96 % within a broadband wavelength. The evaporation rates of DMF and NMP for XPBI under one sun were 3.63 and 1.44 kg·m−2·h−1, 49 and 127 times higher than that of natural evaporation. After natural sunlight irradiation for 8 h, XPBI evaporated 37.58 and 9.63 kg·m−2 IPA and DMF with organic dye rejection rates of 99.7 %. Furthermore, the simulation and optimization of cotton bud arrangement for organic solvent transport is proven to inhibit the membrane pollution of dye molecules for XPBI. This work demonstrates a low-cost, highly efficient, and stable photothermal membrane evaporator as an energy-saving and low-carbon technical prototype for organic solvent purification.

Superhydrophobic coatings reduce human bacterial foodborne pathogen attachment to woods used in fresh produce harvest and postharvest packing

Wood is reportedly more difficult to maintain in hygienic condition versus other food contact materials, yet its use in produce packing and retail warrants efforts to reduce the risk of microbial pathogen contamination and attachment. This study characterized antifouling capabilities of fluorinated silanes applied to wood used in fresh edible produce handling to render the wood superhydrophobic and less supportive of bacterial pathogen attachment. Pine and oak cubic coupon surfaces were treated with 1% (w/w) silane or left untreated. Treated and untreated coupons were inoculated with Salmonella enterica or Listeria monocytogenes and held to facilitate pathogen attachment for 1, 4, or 8 h. Silane treatment of wood produced significant reductions in the proportions of strongly attaching cells for both pathogens versus loosely attaching cells (P < 0.01). Salmonella attachment demonstrated a dependency on wood treatment; silane-treated wood supported a lower fraction of strongly adhering cells (1.87 ± 1.24 log CFU/cm2) versus untreated wood (3.72 ± 0.67 log CFU/cm2). L. monocytogenes demonstrated significant declines in strongly attaching cells during extended exposure to silane-treated wood, from 7.59 ± 0.14 to 5.27 ± 0.68 log CFU/cm2 over 8 h post-inoculation. Microscopic analysis demonstrated silane treatment increased the surface roughness of both woods, leading to superhydrophobic conditions on wood surfaces, consequently decreasing strong attachment of pathogenic bacteria.

"Honeycomb" Photothermal Lubricated Porous Foam with Low-Temperature, Weak-Light, Anti-Icing/Deicing, and Long-Lasting Lubrication Properties.

The prevalence of icing in nature has become a significant threat to human work and life, prompting the development of more energy-efficient active/passive combination anti-icing/deicing technologies. In order to overcome the disadvantage of the poor durability of superhydrophobic surfaces, lubricated surfaces inspired by nepenthes have been preferred. In this study, a paraffin and silicone oil-infused photothermal foam (PSIPF) with excellent overall performance was prepared using polypyrrole (PPy) as a photothermal conversion material, a mixture of silicone oil and paraffin as a lubricating fluid, and melamine foam (MF) as a carrier. The surface adhesive strength is less than 20 kPa at -20 °C, the melting time is only 1018 s at an irradiance of 200 W/m2 and -20 °C (0.2 sun), and surface droplets do not freeze within 1 h at -10 °C. Furthermore, the surface exhibits excellent mechanical durability and stability, maintaining optimal lubrication properties following repeated cycles of icing/deicing, water rinsing, and immersion for 2 days in acid and alkaline conditions. This photothermal lubricated surface with excellent anti-icing/deicing properties at low temperatures and in weak-light environments provides a wider range of applications for equipment at high latitudes and high altitudes.

Leidenfrost spheres, projectiles, and model boats: Assessing the drag reduction by superhydrophobic surfaces

Superhydrophobic surfaces are expected to reduce drag on bluff bodies moving in water due to the introduction of a thin air layer around the solid and the resulting partial slip boundary condition. The use of Leidenfrost vapor layers, sustained on the surface of a heated metal body is a reliable method to estimate the maximum drag reduction possible due to such air layers. In the past such an approach was used to estimate the drag reduction on a free-falling heated sphere, in which case the form drag is the lead component of the drag force. Here, we extend this approach to evaluate the effect of the thin gas layers on the hydrodynamic drag of free-falling streamlined projectiles and towed model boats, where the form drag is minimal, and the skin friction drag is the lead component of the drag force. By comparing the drag for streamlined bodies with and without sustained air-layers, we see only incremental drag reductions, for the sub-critical Reynolds number tested herein. The same is true for towed model boats. These results hold both for superhydrophobic surface treatments and Leidenfrost vapor layers. Thus, we concluded that for the investigated range of sub-critical Reynolds numbers, the skin friction drag is less sensitive to the effect of the thin gas layers compared to the form drag. These novel findings have important implications for the practical potential of energy savings using gas layers sustained on superhydrophobic surfaces.

Droplet Bottom Expansion and Its Wettability Control Mechanism Based on Macroscopic Defects.

Biomimetic surfaces with special wettability have received much attention due to their promising prospects in droplet manipulation. Although some progress has been made, the manipulation of droplets by macroscopic defects of the millimeter structure and the wetting-state transition mechanism have rarely been reported. Herein, inspired by lotus leaves and desert beetles, biomimetic surfaces with macroscopic defects are prepared by laser processing and chemical modification. Various functions of droplet manipulation are achieved by controlling the millimeter-scale macroscopic defects, such as droplet capture, motion trajectory changing, and liquid well. And a droplet bottom expansion phenomenon is proposed: wetting-state transition in superhydrophobic regions around defects. The "edge failure effect" is proposed to explain the force analysis of droplet capture and the droplet bottom expansion to distinguish it from the adhesion phenomenon presented by the droplet sliding. 53.28° is defined as the expanded saturated angle of the as-prepared surface, which is used to distinguish whether the defect could cause the droplet bottom expansion. An enhanced edge failure effect experiment is designed to make the droplet bottom expansion more intuitive. This work provides a mechanistic explanation of the surfaces that utilize macroscopic defects for droplet manipulation. It can be applied to the monitoring of droplet storage limits, providing a perspective on the design and optimization of superhydrophobic surfaces with droplet manipulation.

Green and Abrasion-Resistant Superhydrophobic Coatings Constructed with Tung Oil/Carnauba Wax/Silica for Wood Surface.

As a renewable, environmentally friendly, natural, and organic material, wood has been receiving extensive attention from various industries. However, the hydrophilicity of wood significantly impacts the stability and durability of its products, which can be effectively addressed by constructing superhydrophobic coatings on the surface of wood. In this study, tung oil, carnauba wax, and silica nanoparticles were used to construct superhydrophobic coatings on hydrophilic wood surfaces by a facile two-step dip-coating method. The surface wettability and morphology of the coatings were analyzed by a contact angle meter and scanning electron microscope, respectively. The results suggest that the coating has a micron-nanosized two-tiered structure, and the contact angle of the coating is higher than 150° and the roll-off angle is lower than 10°. Sandpaper abrasion tests and UV diffuse reflectance spectra indicate that the coatings have excellent abrasion resistance and good transparency. In addition, the coated wood shows excellent self-cleaning and water resistance, which have great potential for applications in industry and furniture manufacturing.

Superhydrophobic films with high average transmittance in infrared and visible range prepared by iCVD technology

Superhydrophobic high-transmittance antireflection coatings (ARCs) have significant potential for applications in optical devices such as microscope lenses, as well as in daily life for windows and glasses. However, current technologies encounter challenges in achieving superhydrophobicity on surfaces of ARCs. Here, we successfully combine the initiated chemical vapor deposition (iCVD) process technology with surface structuring to obtain a wide-spectrum transmission-enhanced coatings exhibiting self-cleaning and superhydrophobic properties. Compared with the bared substrate, the average transmittance of the worm-like/nanocones structure increases from 93.0 % to 95.1 %. Furthermore, an impressive water contact angle of 177.1° and a sliding angle of less than 1.0° are achieved. Moreover, the transmittance and hydrophobic properties can be easily adjusted by manipulating morphology of the film. The formation mechanism and fabrication processes of nanocones and worm-like structures are comprehensively investigated for flexible adjustment of the film properties. This provides a practical solution for the application of ARCs in various scenarios.

Synthesis of polymeric superhydrophobic coatings of nickel stearate for excellent corrosion resistance, self-cleaning, and photodegradation

Superhydrophobic coatings (SHCs) have been widely reported for various applications; however, the practical applications of SHCs have been restricted by recurrent preparation methods, complex equipment, and low mechanical robustness. The development of a simple, low-cost, and effective superhydrophobic coating remains a challenge. Here, we reported a simple way to fabricate the SHC by using fluoropolymeric suspension of nickel stearate nanoparticles (Ni-St-NPs) on the copper and other substrates. The surface of copper coated by SHC showed a static contact angle of 161 ± 1º and a sliding angle of 2º. Scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometer were used to determine the surface morphology, elemental content, crystal structures, chemical bonding, and structure of the SHCs. The fluoropolymeric coating of Ni-St-NPs showed excellent anti-corrosion and self-cleaning with mechanical durability and stability. Photodegradation of methylene blue (MB) and rhodamine B (RhB) dyes were done at 25 °C and obtained the degradation efficiency of 99 % and 98.1 %, respectively. The existence of self-cleaning, mechanical durability, and photocatalytic properties makes the fluoropolymer coating of nickel stearate a very promising superhydrophobic coating material for multifunctional applications.

A Superhydrophobic Coating with Sturdy Abrasion and Weather Resistance

A Superhydrophobic Coating with Sturdy Abrasion and Weather Resistance

Enhanced surface performance of insulating ceramic by plasma polymerization with nanosecond-pulse dielectric barrier discharge: Insight into the effect of the repetition frequency

Insulating ceramics are widely used in power systems, but their high polarity makes them prone to wet and pollution flashover. In this paper, an Ar/polydimethylsiloxane dielectric barrier discharge excited by a parametric nanosecond-pulse power source is utilized for plasma polymerization to enhance ceramic surface insulating performance. Diagnosis of the discharge characteristics and surface physiochemical properties is conducted at different repetition frequencies to investigate the mechanism associated with the relationship between repetition frequency and the plasma polymerization process. The results indicate that a superhydrophobic surface can be achieved at repetition frequencies above 2 kHz. This transformation brings about multiple effects, including a decrease in surface polarity, an increase in charge dissipation, and an improvement in surface dry and wet flashover voltages. It is discovered that the discharge mode shifts from homogeneous to filamentary due to the memory effect of high repetition frequencies. Additionally, several filaments are generated simultaneously during a single pulse, facilitating the polymerization reactions. For high repetition frequencies, a low-polarity silicon-containing film with micro-nanometer structures is deposited on the ceramic surface, while scattered polymer fragments are generated on the surface without a cross-linked film for repetition frequencies below 2 kHz, despite longer treatment durations.

SUPERHYDROPHOBIC AND ANTIBACTERIAL COATINGS ON VARIOUS COTTON FABRICS USING ZNO AND AESO

Superhydrophobic coatings on cotton utilized in medical applications like hospital gowns and bed linens to offer a protective barrier against fluids and bacteria. Masks were worn with different types of materials. In this study, various cotton employed ZnO and AESO to effectively decrease the surface energy of cotton fabric via a Schiff base reaction. This chemical transformation resulted in the formation of a textured surface structure that exhibited robust adhesion qualities. The study demonstrates that the superhydrophobic coating on silk fabric increases 153. 59%. The coating on silk provides a reference for fabric types with ZnO and AESO coatings.

Suppression of coffee rings by controllable nanoparticle enrichment through superhydrophobicity-enabled dynamic evaporation

Coffee rings formed by evaporation of analyte-containing droplets are widely observed in micropatterning, bio-arrays, and trace detection. The coffee-ring effect caused by contact line pinning significantly affects the detection uniformity and sensitivity. Here, we propose a simple and operable method to effectively suppress coffee rings through controllable nanoparticles aggregation by superhydrophobicity-enabled dynamic evaporation. The gold nanoparticles (AuNPs) deposition footprint formed after dynamic evaporation on an integrated superhydrophobic surface was reduced by ∼3 orders of magnitude compared to that of non-interventional evaporation. Detailed experiments, numerical simulations, and theoretical studies have revealed that substrate wettability, temperature and droplet motion behaviors play significant roles in suppressing coffee-ring effect. More critically, based on the force mechanism of AuNPs at the interface/contact line, universal mathematical models and regime maps were established to classify the different deposition modes for AuNPs under different evaporation conditions by introducing dimensionless parameter G, revealing the enrichment mechanism of AuNPs in droplets under superhydrophobicity-enabled dynamic evaporation. The accuracy of the theoretical model and enrichment mechanism was demonstrated through the single-molecule detection of rhodamine 6G with excellent sensitivity (10–17 M, enhancement factor ∼1013) and perfect uniformity (relative standard deviation ∼5.57 %), which provides a valuable guide for research and applications of nanoparticle aggregation.

Water-Borne Photo-Thermal Superhydrophobic Coating for Anti-Icing, Self-Cleaning and Oil–Water Separation

Superhydrophobic coatings with photo-thermal effects have advantages in anti-/de-icing and self-cleaning. Here, an eco-friendly and low-cost fabrication of superhydrophobic coating was proposed by spraying a water-borne suspension including carbon black and paraffin wax onto substrate-independent surfaces. The a water-borne suspension coated on stain steel plate showed a strong water-repellence, delaying the ice freezing time to 665 s, which is much higher than that of bare stain steel plate (210 s) under the same experimental condition. The ice-melting time was measured as 120 s under a solar irradiation of 0.1 W/cm2, while the control group had no sign of ice-melting during the same time. As a concept of proof, the self-cleaning, anti-corrosion, and oil–water separation were enabled by spraying the water-borne suspension on various substrates, demonstrating its diverse performances. Hence, the water-borne superhydrophibic coating provides an efficient, safe, and sustainable solution for wettability-related applications.

Superhydrophobic surface with good anti-icing properties and high durability

Ice formation is a widespread phenomenon in nature, and superhydrophobic surfaces, due to their excellent hydrophobic properties, are extensively employed in the field of ice prevention. In this study, silane coupling agent (Si69) is used to modify the petal-like SiO2 surface to reduce its surface energy. An epoxy/benzoxazine/Si69-SiO2 ternary mixed superhydrophobic surface is constructed on basalt fiber fabric using a spray and thermal curing method. Examination of the data reveals that a 1:2 proportion of Si69-SiO2 and epoxy/benzoxazine yields a surface whose hydrophobicity is quantified by a water contact angle measuring 165±2°. The water droplet bounces three times on the surface, demonstrating optimal superhydrophobicity. Compared to samples without the addition of Si69-SiO2, the icing time is extended by approximately 4.83 times. Following 30 iterations of freeze-thaw processes, the surface retains its exceptional water-repellent properties, demonstrating excellent ice-phobic stability. Furthermore, the surface maintains its superhydrophobic performance, demonstrating excellent mechanical durability, even after being subjected to friction with SiC sandpaper (220 mesh) for 200 cm under a pressure of 3.2 Kpa and reciprocal friction for 30 minutes under a 50 g load. The surface can withstand over 12 hours of acid and alkali corrosion, and it also possesses excellent self-cleaning capabilities.

A fluorine-free and high-robustness photothermal self-healing superhydrophobic coating with long-term anticorrosion and antibacterial performances

Superhydrophobic surface is a promising strategy for antibacterial and corrosion protection. However, the use of harmful fluorine-containing materials, poor mechano-chemical stability, the addition of fungicides and poor corrosion resistance often limit its practical application. In this paper, a high-robustness photothermal self-healing superhydrophobic coating is prepared by simply spraying a mixture of hydrophobically modified epoxy resin and two kinds of modified nanofillers (carbon nanotubes and SiO2) for long-term anticorrosion and antibacterial applications. Multi-scale network and lubrication structures formed by cross-linking of modified carbon nanotubes and repeatable roughness endow coating with high robustness, so that the coating maintains superhydrophobicity even after 100 Taber abrasion cycles, 20 m sandpaper abrasion and 100 tape peeling cycles. The synergistic effect of antibacterial adhesion and photothermal bactericidal activity endows coating with excellent antibacterial efficiency, which against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) separately reaches 99.6% and 99.8%. Moreover, the influence of modified epoxy resin, superhydrophobicity, organic coating and coating thicknesses on the anticorrosion of magnesium (Mg) alloy is systematically studied and analyzed. More importantly, the prepared coating still exhibits excellent self-cleaning, anticorrosion and antibacterial abilities after 20 m abrasion. Furthermore, the coating exhibits excellent adhesion (level 4B), chemical stability, UV radiation resistance, high-low temperature alternation resistance, stable heat production capacity and photothermal self-healing ability. All these excellent performances can promote its application in a wider range of fields.

Development of superhydrophobic fractal surfaces using Silica nanoparticles based on polylactic acid through molding technique

This research introduces a novel approach to creating superhydrophobic surfaces on polymer substrates. The objective is to develop a general method for producing various types of superhydrophobic polymer surfaces using modified nanoparticles, as well as making Unplasticized PolyVinyl Chloride(UPVC) and polylactic acid hydrophobic. To achieve this goal, we investigate the circulation of a rotating cover, pressure, and pressure time. We embed modified silica nanoparticles onto UPVC boards, which confirms surface hydrophobicity with a contact angle of 155° and a sliding angle of 6–7° for water droplets. Under specific conditions, including a suspension concentration of 10 g/L, coating time of 5 seconds, temperature of 155°C, rotation speed of 400 rpm, and pressure of 2 MPa with a pressure time of 4 minutes, we achieve superhydrophobicity on PVC boards, resulting in contact angles of 150–160°. Additionally, we find that the sliding angle of water droplets is less than 10°.

Engineering of ceramic membranes with superhydrophobic pores for different size water droplets removal from water-in-oil emulsions

Superhydrophobic (SHB) ceramic membrane surfaces have proved their superiority in water-in-oil (W/O) emulsion separation. However, the construction of ceramic membranes with SHB pores remains challenging and the interaction between the SHB pores and water droplets is still unclear. Herein, by growing uniform ZnO nanoclusters (NCs) onto the SiC grains of a symmetric SiC ceramic membrane and then grafting with triethoxy(octyl)silane, a series of ZnO NCs@SiC membranes with SHB pores were prepared. Prior to secondary hydrothermal synthesis ZnO NCs, the small-sized ZnO nanoparticles (NPs) were grown onto the SiC grains via a sol–gel process. All the ZnO NCs@SiC membranes with SHB pores showed improved water removal performance from W/O emulsions compared with that of the pristine membrane. The optimal membrane with SHB pores displayed a pore size of 0.19 μm with a water contact angle of 163.96°. The smaller water droplets in W/O emulsions, the membrane pores are easier to be polluted. When separating a 1000 ppm W/O emulsion with a water droplet size of 500 nm at a transmembrane pressure of 0.5 bar, the water rejection reached 98.90 %, and the steady-state oil flux was 92.99 L·m−2·h−1. Based on the separation experiments, the separation mechanism was revealed. This work provides significant perceptions into constructing SHB pores of ceramic membranes, which might be useful for other possible applications.

Facile fabrication of microstructured superhydrophilic and superhydrophobic STS316L

The enhancement of the wettability characteristics in stainless steel holds substantial significance for the application of inhibitor coatings. Investigating a s surface design along with assessing the influences of roughness, surface topography, and chemical heterogeneity on wettability has been a primary focus. In this context, the manipulation of stainless steel surface properties has gained significant attention, specifically for the purpose of fine-tuning wettability. Despite this, uncomplicated surface treatment techniques for stainless steels remain insufficiently established. This study presents a simple etching and oxidation approach for tuning the wettability of stainless steel (STS316L). Through etching and oxidation of STS316L, a superhydrophilic wetting state was achieved (contact angle ∼ 2°). Subsequent application of a monolayer coating led to the reversal of wettability from superhydrophilic to superhydrophobic (contact angle ∼ 168°). Additionally, the proposed methodology for STS316L surface treatment opens up broad expansion possibilities for the applications of superhydrophobic surfaces.