Superhydrophobic Surfaces Research Articles

Superhydrophobic synergistic antibacterial ZrO2-based surfaces with tertiary hierarchical structures fabricated by femtosecond laser texturing and surface modification

Zirconia (ZrO2) is a hard and brittle dental implant material without anti-infective property. This work reports the preparation of a tertiary micro-nano hierarchical structure on a ZrO2 surface via femtosecond laser texturing combined with magnetron sputtering deposition of an Ag layer (Ag/ZrO2), aiming to achieve a superhydrophobic synergistic antibacterial effect. Laser-scanning pitch and Ag layer thickness were systematically optimized for obtaining the tertiary hierarchical structure. The wettabilities, antibacterial properties and durabilities of various ZrO2 and stearic acid modified Ag/ZrO2 (S-Ag/ZrO2) surfaces were further tested and comparatively analyzed. The results revealed that the optimal process parameters were a laser-scanning pitch of 30 μm and an Ag layer thickness of 100 nm. The as-obtained S-Ag/ZrO2 sample displayed a tertiary micro-nano hierarchical structure, which was featured by a periodic regular conical micro-convex structure covered with ZrO2 nano-protrusions and Ag nanoparticles. This structure could not only greatly reduce the solid-liquid contact area to achieve outstanding superhydrophobicity and durability, it could also sustainably release bacteria-killing Ag+ to obtain an antibacterial ratio of 95.1 % and ensure a long-term antibacterial effect. In addition, the optimal S-Ag/ZrO2 sample having this structure showed a PC12 cell survival rate of up to 81.75 %, demonstrating its good biocompatibility. This work may be of great inspiration and reference for the expansion of the use of ZrO2 in dentistry.

A superhydrophobic mortar with ultra-robustness for self-cleaning, anti-icing, and anti-corrosion

Superhydrophobic cement-based materials are promising candidates to alleviate the performance deterioration of concrete constructions caused by water penetration. However, the weak mechanical performance of superhydrophobic surfaces, and severe reduction in compressive strength due to bulk modification, present significant challenges for the application of superhydrophobic cement-based materials. In this work, a superhydrophobic mortar (S-mortar) was prepared using a facile and economical method by surface micro-nano roughness construction and matrix silane modification, and nano-silica was introduced to compensate for the strength loss. The obtained S-mortar exhibits superb surface mechanical durability and chemical stability, no significant decrease in superhydrophobic property after sandpaper rubbing, knife scratches, and exposure to extreme temperatures, while even new surfaces exposed by cutting and powders obtained by grinding possess excellent water repellency. Furthermore, the superhydrophobicity endows the S-mortar with self-cleaning, anti-fouling, anti-icing, anti-freezing, and anti-corrosion properties. This approach creates a balance between superhydrophobic property and mechanical performance, broadening application prospects of superhydrophobic cement-based materials.

Superhydrophobic surface preparation and tribological properties of Ti-1023 alloy with parallel groove

Superhydrophobic surfaces are increasingly vital in materials science due to their exceptional properties such as water repellency, self-cleaning, and corrosion resistance. However, fabricating these surfaces on metal substrates poses significant challenges, including the need for precise control over micro- and nano-structures and ensuring their durability under mechanical and environmental stresses. This study introduces a novel fabrication method for superhydrophobic surfaces on Ti-1023 alloy utilizing nanosecond laser ablation followed by chemical modification with perfluorodecyltriethoxysilane. This technique allows precise microstructural adjustments and enhanced durability. Our findings demonstrate that a groove spacing (GS) of 100 μm optimizes the water contact angle to 162.8° and the water sliding angle to 7.8°. Meanwhile, a GS of 200 μm minimizes the coefficient of friction to 0.176 under starved-water lubrication conditions. These advancements demonstrate the method’s effectiveness in reducing wear and friction, and highlight its potential in aerospace and other high-performance industries.

Jumping behavior of water nanodroplets on a superhydrophobic surface in high Ohnesorge number (Oh) regime

The coalescence-induced jumping of nanodroplets on superhydrophobic surfaces has recently gained research attention due to its application in energy harvesting, self-cleaning, and cooling of nanoscale electronic devices. This study aims to investigate the jumping behavior of water nanodroplets in a high Ohnesorge number regime, where 0.45 < Oh < 1 and identify the critical size of droplets where jumping terminates. The study utilized molecular dynamics simulations to analyze the jumping characteristics of droplets ranging from 1.5 nm to 7 nm in radius. The findings of this research developed a universal jumping mechanism for droplets of all sizes, identified the lower limit of droplet size, below which coalescence-induced jumping does not occur, and explained a special phenomenon of jumping velocity becoming maximum before it approaches zero. The study also investigated how jumping terminates due to the size difference between droplets. These findings align well with prior micro-scale studies and experimental predictions. Surface energy, viscous dissipation, kinetic energy, and varying surface tension have been identified as the dominating factors influencing nanoscale droplet jumping at such a high Oh regime. The findings will provide insights for developing various applications at this scale.

Super hydrophobic self-stratified coating based on epoxy terminated polyurethane/siloxane nano-composite

ABSTRACT Recently, the application of superhydrophobic coatings on insulators has emerged as an effective strategy for mitigating risks and damages. In the current investigation, a superhydrophobic coating formulated with polyurethane (PU) prepolymer and polydimethylsiloxane (PDMS) has been developed, featuring a surface layer of SiO2 nanoparticles (NPs) modified with fluoroalkyl silane (FAS). The identification of peaks within the ranges of 567, 650, 747, and 898 cm− 1, corresponding to CF, CF₂, and CF₃ bonds, along with the reduction of the peak associated with the hydroxyl group around 3433 cm− 1, substantiates the interaction between FAS13 and SiO2 nanoparticles. The resultant coating exhibited a 39% increase in hydrophobicity compared to the coating without nanoparticles. The surface modification of nanoparticles resulted in an escalated degradation rate for the USMN sample, reaching a temperature range of 300 to 400°C. This phenomenon is attributed to the interaction between the hydroxyl groups on the nanoparticle’s surface and the Si-O bonds present in the FAS13 composition, leading to increased thermal resistance of the nanoparticle. This study successfully produced a PDMS/PU coating utilizing modified SiO2 particles through a self-stratified approach. This coating acts as an adhesive layer for high-voltage insulation surfaces, effectively protecting against water intrusion and dust accumulation.

Superhydrophobic performance of aluminum textured with a picosecond laser

Aluminum is a common and light engineering metal with high strength, good processability, corrosion resistance, high electrical conductivity, and strong recyclability, properties that allow its wide use in different fields. Strengthening the surface properties of aluminum materials can not only enable aluminum materials to be applied to complex environments but also extend their service life. In this study, two kinds of micro–nano structures—unidirectional micro-grooves and grid micro-grooves—were prepared on the surface of 1060 aluminum using picosecond-laser direct etching, so that its surface can attain superhydrophobic properties and enhance its application performance. The effect of the scanning interval of picosecond laser on the hydrophobic performance was investigated, and the findings indicate that the hydrophobic properties are most effective by using scanning interval of 20 μm. The scanning electron microscope (SEM) and atomic force microscope (AFM) analyses revealed the formation of a micro-nano structure resembling nanoflower particles on the laser-treated aluminum surface, which contributed to increased surface roughness. EDS analysis indicated an increase in carbon (C) content, likely due to the adsorption of organic molecules from the air, which further promoted hydrophobicity. X-ray diffraction spectrometry (XRD) and X-ray photoelectron spectroscopy (XPS) provided insights into the surface chemistry and the presence of various elements and compounds. The superhydrophobic aluminum surfaces demonstrated remarkable stability and self-cleaning capabilities, desirable traits for many practical applications. This study provides a simple and rapid method for preparing superhydrophobic materials on aluminum surfaces and has potential practical application value.This innovation paves the way for the development of high-performance aluminum materials suitable for a wide range of environments and uses.

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.