Water Repellency Performance Research Articles

Highly transparent and highly hydrophobic coating for outdoor camera window glass: Fabrication, transparency, and hydrophobicity

Highly transparent, superhydrophobic coatings are highly desirable for maintaining long-lasting clarity for outdoor camera windows. In this study, the authors present a simple approach to create a wide–range anti-reflective and highly hydrophobic layer on a glass surface. This is accomplished through a hydrothermal alkali etching process combined with a dip-coating process using 1 H, 1 H, 2 H, 2 H-Perfluorooctyltrimethoxysilane (POTS). The sample, etched for 20 h and modified by POTS, exhibiting an average transmittance of 96.5 %, a water contact angle (WCA) of 140° and a sliding angle (SA) of 40°. The results of the water spray experiment indicate this surface exhibits excellent water repellent performance, preventing water droplets larger than 0.01 mm in size. The relationship between optical transmittance and etching depth was thoroughly studied, revealing that an etched depth ranging from 200 nm to 600 nm yields optimal wide-spectrum anti-reflective properties. Furthermore, the influence of surface roughness on apparent WCA and SA was investigated. It was found that root mean square (RMS) roughness can be an effective factor to predict the apparent WCA of a surface, while both the RMS roughness and morphological structure affect the SA.

Nanofluid Droplet Impact on Rigid and Elastic Superhydrophobic Surfaces.

Ice accumulation on cold surfaces is a common and serious phenomenon that exists in numerous industrial fields, such as power transmission, wind turbines, and aircraft. Despite recent efforts in mitigating ice accumulation on the cold surface, it remains a challenge to achieve robust anti-icing on the cold surface in terms of nanofluid droplet. Here, we report a rigid superhydrophobic Cu surface and an elastic polydimethylsiloxane (PDMS) superhydrophobic surface to enhance water-repellency performance, characterized by a significant reduction in contact time and a decrease in the spreading ratio. As for the rigid superhydrophobic Cu surface, the underlying mechanism is ascribed to the existence of stable air cushions between the micropillar array, which reduce the contact area and further suppress the heat conduction. As for the elastic PDMS superhydrophobic surface, the rapid detachment of the nanofluid droplet relies on superior surface elasticity, which can further suppress the nanofluid droplet splashing at a high impacting velocity. We believe that this work can provide a new view for the improvement of water-repellency for a wide range of applications.

Synthesis of Long Alkyl and Fluoroalkyl Substituted Siloxane Copolymers for the Water Repellency of Rammed Earth Walls.

Rammed earth in a built environment has vapor diffusion characteristics and humidity control abilities, each of which is respectively attributed to the porous structures and the hydrophilic properties. Indeed, these structures and properties allow for the easy absorbance of water particles, hence affecting the durability of a rammed earth wall. This paper presents the water-repellency method for rammed earth walls, which utilizes siloxane copolymers containing fluorine. The water-repellent properties are investigated by measuring the contact angle, water absorption rate, and compressive strength after spray-coating with the synthesized siloxane copolymers on the surface of the rammed earth specimens under study. The water contact angle of the specimen, coated with a siloxane copolymer containing 10 mol.% of a silane monomer with a fluorine group, is about 140°. The water absorption of the specimen obtained after immersing in water for 24 h is low, at about 3.5 wt.%. In addition, the compressive strength remains more than 80% of the corresponding strength of the specimen which is not immersed in water. It is confirmed that the use of a 10% by volume of the siloxane copolymer containing the fluorine group may enhance the water-repellent performance and economic competitiveness.

Preparation and properties of a simple super‐hydrophobic carbon fiber composite surface

AbstractSuper‐hydrophobic surface is widely used in waterproof, antifouling, and anticorrosion fields because of its unique wetting characteristics. However, the rough structure of super‐hydrophobic surface is easily damaged in service, which leads to the loss of various properties, making it difficult to apply super‐hydrophobic surface on a large scale in actual production. In this paper, epoxy resin was used as adhesive, mixed with hydrophobic silica particles and sprayed on the surface of carbon fiber composites. After curing, the surface of super‐hydrophobic carbon fiber composites with contact angle of 158 ± 2° and sliding angle of 1 ± 0.5° was formed. The surface had excellent dynamic water repellent performance, and the droplets could bounce more than three times on the surface. Furthermore, the super‐hydrophobic surface had excellent wear resistance and mechanical stability. After the friction damage test, the surface structure of the sample was slightly damaged. The amount of wear was small, and the surface was still in super‐hydrophobic state. Through soaked in solutions with different pH values, the microstructure of the surface was not obviously damaged by corrosion, the contact angle of water droplets was greater than 155°. The preparation method of super‐hydrophobic surface of carbon fiber composite proposed in this study is simple and rapid, and the prepared surface has excellent performance, the practical application of super‐hydrophobic surface is promoted.

Water flow tuned by micro/nano hierarchical structures fabricated through two-photon polymerization

Two-photon polymerization (TPP) is a sub-classification of vat photopolymerization. It has been widely used to fabricate micro/nano hierarchical structures that have the potential to be used to tune the fluid flow in chips. The present work first studied the influence of laser power on the feature size of TPP-fabricated 2D structures. It was found that the increase of laser power from 1.0 μW to 1.4 μW leads to the feature size increasing from 203 nm to 307 nm. Then, the effect of scanning parameters on the accuracy and surface quality of 3D structures was investigated. The arrangement of the voxels at different scanning strategies explains the mechanisms of the variation of accuracy and surface roughness. Finally, the pinecone structures with micro/nano hierarchical features were built and evaluated for their water repellence. The increase in the number of rows of pinecone structures significantly enhances the water-repellent performance.

Research on waterproof performance and mechanism of organic silicon hydrophobic material for roadbed soil

In order to provide a new method for inhibiting the rise of capillary water, the influence of hydrophobic materials on the water-repellent performance of roadbed soils was investigated and the influence of hydrophobic substance dosage per unit area and action time on soil impermeability was analyzed. The results demonstrate that the permeability coefficient of the soil reduces dramatically as the amount of hydrophobic material per unit soil area increases, and start with an increment but later turned into a decrement with the action time. The permeability coefficient of the soil was 0.7892×10−7 cm/s as the minimum as with a drop of 98.86 percent under conditions of 125 g per unit area and an action time of 24 h. Furthermore, the organic silicone hydrophobic material will eventually form a dense hydrophobic film to block the infiltration of external water, thereby enhancing the hydrophobicity of the soil.

Improving surface performance of silicone rubber for composite insulators by multifunctional Nano-coating

Composite insulator is an important component of outdoor insulation systems. It works in complex environments and faces a series of problems such as surface contamination, loss of hydrophobicity, and accumulation of surface charges, which may eventually lead to flashover. Aiming to solve these problems in a simple and scalable method, we propose a multifunctional nano-coating based on SiO2/PDMS/EP. By the combination of multiscale structure and low surface energy modification, this coating shows excellent water-repellency performance, a large contact angle greater than 160° and a small rolling angle near 0° are achieved on coated silicone rubber, which enables the surface with excellent self-cleaning performance. Benefiting from the multiscale roughness, the heat transfer is inhibited by the reduced contact area, which further slows down the icing process on coated silicone rubber. The de-icing force on coated silicone rubber is also smaller than that on pristine silicone rubber. This coating also introduces many shallow traps to the surface, which is beneficial to the fast surface charge dissipation in a short time. Besides, the high water-repelling ability can promote the droplet to roll away under the action of electrical field force, which alleviates the electrical distortion caused by the droplets. As a result, the wet flashover voltage of coated silicone rubber is 60% higher than that of pristine silicone rubber. This multifunctional coating is a facile, scalable, and effective approach to improving the comprehensive surface performance of insulators.

Research on the mechanical and water-repellent properties of bionic carbon fiber reinforced plastic composites inspired by coelacanth scale and lotus leaf

Carbon fiber reinforced plastic (CFRP) laminates are widely used in vessel side plate, underwater propeller, and submarine oil pipeline because they possess superior specific strength and hydrophobicity compared with metal materials. However, conventional CFRP laminates are limited by insufficient mechanical properties and incompetent water-repellent performance. Herein, a biomimetic double-helicoidal superhydrophobic laminate (BDHSL) was designed and manufactured through a method combining hot press forming and two-step spraying. The BDHSL was composed of double-helicoidal (inspired by coelacanth scale) carbon fiber prepreg and SiO2-based coating with multiscale hierarchical structures (inspired by lotus leaf), which displayed excellent mechanical properties and water-repellency. Besides, mechanical tests were carried out systematically. Remarkably, the peak impact force of the BDHSL at the impact energy of 20 J was 2865.25 N, which increased by 136.88% compared with traditional unidirectional laminate (UL 1209.56 N). Meanwhile, the finite element simulation was conducted using 3D Hashin's failure criteria. The simulation results showed that the predicted stress-deflection curve for four types of laminates correlated well with experimental results. Moreover, the water contact angle of BDHSL reached approximately 156.5°, which indicated its superhydrophobicity. What is more, the durability and water-repellency of the SiO2-based coatings were investigated, which further confirmed its potential underwater applicability. The investigations in this work offer a promising way to effectively design and fabricate exquisitely structured CFRP laminates with hierarchically textured coatings that are more suitable for various marine applications under practical conditions, such as offshore oil drilling platform, autonomous underwater vehicle, high-speed ship, and so forth.

Toward Surfaces with Droplet Impact Robustness and Low Contact Angle Hysteresis

AbstractSuperhydrophobic surfaces show excellent water repellent performance. However, liquid impalement occurs when a droplet impacts on the surface at high velocity. To achieve higher resistance to liquid impalement at the same scale, a dense array of structures or structures with pinning at the structures top are typically used, but they also lead to increased contact angle hysteresis and higher energy dissipation. Changing the structure side wall shape can help to maintain low hysteresis and withstand high impact energy at the same scale. Droplet contact angle, contact angle hysteresis and droplet impact experiments are performed on both conical and cylindrical pillar surfaces. Comparing conical and cylindrical pillar structures with the same pitch and height, it is found that cylindrical pillars exhibit higher critical Weber number but result in larger contact angle hysteresis and larger liquid residue size when above a critical Weber number. A proper design of conical structures can maintain large contact angle, low hysteresis, strong resistance to impalement, higher number of bouncing and smaller liquid residue size. In addition, the critical Weber number for the conical structures in this work is higher than micro‐patterned pillar surfaces at the same pitch range, implying that we improve the anti‐wetting performance further.

Durability of the hydrophobic treatment on brick and mortar

Hydrophobization lessens the water absorption by facade materials and is thus presumed to reduce moisture problems in internally insulated facades. However, to do this it should retain the water repellency performance throughout aging. The aim of this study is to evaluate the impact of aging on the durability of the hydrophobic treatment on bricks and mortars. The resulting absorption coefficient, after 635 repeating artificial aging cycles of alternating UV radiation (102 min) and water exposure (18 min) reveals that the hydrophobic layer maintains its water repellency performance both in brick and mortar. The samples were treated with two different water repellent agents in different concentrations and tested for capillary water uptake. Additionally, the findings show that cycles of weathering could contribute positively to further reduction of the absorption coefficient of hydrophobized brick and mortar samples. Subsequently, Karsten tube tests on samples from artificial aging illustrate the same water repellency performance as mock-up walls exposed to ambient conditions, six years after being hydrophobized. Contact angle measurements before and after artificial aging reveal that the beading effect declines through aging. However, the beading effect seems to be just a surface effect affected by UV-light. Moreover, after aging, hydrophobized brick and mortar samples, tested by visual inspection, maintain their appearance while untreated samples show signs of efflorescence. In total, these findings indicate that the water uptake of hydrophobized brick or mortar remains very low after aging including water spraying and UV light.

Superhydrophobic and oleophobic dual-function coating with durablity and self-healing property based on a waterborne solution

A superhydrophobic surface is typically constructed by combination of both low surface energy substance and high roughness microstructure. Although these surfaces have been widely used in the application of self-cleaning, water harvesting and anti-icing, the problems of organic solvents during the preparation process and the undesirable durability have largely limited their practical application. This paper describes a new concept and derived environmental friendly method based on a waterborne solution for the fabrication of durable superhydrophobic and oleophobic surfaces with self-healing property. In this concept, aluminum oxide particles were employed to construct the rough microstructure, fluorosurfactant and fluorinated alkyl silane were employed as low surface energy materials. The obtained surfaces coated on different substrates (glass, wood, fabric, polymer, metal) showed not only excellent water repellent performance with water contact angle larger than 150° and sliding angle is less than 10° but also oleophobic for some low surface energy organic liquid such as glycol, oleic acid, cooling oil and dimethyl formamide. The surfaces show excellent durability to solutions with different pH, abrasion resistance and self-healing by heating the oxygen-plasma-destroyed surface. The proposed coatings with excellent superhydrophobic and oleophobic performance will demonstrate the potential application in self-cleaning and antifouling.

Synthesis of a novel metal-organic nanocomposite film (MONF) with superior corrosion protection performance based on the biomimetic polydopamine (PDA)-based molecules and Sm2O3 particles on the steel surface

In recent years, the nanocomposite films have been utilized for the metals' corrosion resistance enhancement. In this research, an eco-friendly samarium (III) and bio-compatible polyodopamine-based biopolymer have been applied to mitigate the corrosion of steel through the construction of a hybrid film with effective anti-corrosion potency. For this purpose, the PDA micro/nano-particles were synthesized via two well-known self-polymerization and oxidant-facilitated methods. Then, they were introduced into the Sm (III)-based chemical modification bath, and the resulting solutions were sprayed on the steel surface continuously. The steel panels coated with samarium-oxide nanofilm, as well as the Sm-PDA composite coating, have shown excellent water-repellency performance. Results evidenced 34% enhancement in the water contact angle (CA) and a 74% decrease in surface free energy (γs). Also, the SEM/EDS, XRD, and FT-IR analyses results revealed that the great surface hydrophobicity characteristic of the Sm-PDA modified sample is because of the synergistic effect of the nano-roughness of the Sm-nano film and the micro-scale roughness of the PDA particles. In addition, the XRD and FT-IR analysis outcomes affirmed the development of the films composed of the samarium oxide and PDA on the treated steel surface. The EIS and polarization test results revealed that via the steel surface treatment by Sm-PDA film, the total resistance (Rt) and icorr values increased/decreased for 4-fold and 65%, respectively. The Rt of the steel sample subjected to 0.6 M NaCl solution for 96 h is about 1163 (Ω.cm2), while this value for the Sm-treated, Sm-PDAS, and Sm-PDAO samples was 2778, 2915 and 4735 (Ω.cm2), respectively. Overall, the results confirmed the high water-proof and superior anti-corrosion potency of the composite Sm-PDA film.

Preparation of tetrafluoro‐λ6‐sulfanyl bridged‐bonding perfluoroalkyl styrene and its emulsion copolymerization with acrylate monomers for cotton fabrics finishing

Abstract4‐(Perfluorobutyl)styrene, 4‐(Perfluorohexyl)styrene, 4‐[Perfluorobutyl(tetrafluoro‐λ6‐sulfanyl)]styrene (C4F9SF4styrene), and 4‐[Perfluorohexyl(tetrafluoro‐λ6‐sulfanyl)]styrene (C6F13SF4styrene) were prepared in two or three steps. The short‐chain perfluoroalkyl groups are modified through the insertion of tetrafluoro‐λ6‐sulfanyl linked groups (SF4). The prepared perfluoroalkyl styrene acts as functional monomers to react with butyl acrylate, methyl methacrylate, and hydroxyethyl methacrylate for emulsion copolymerization to obtain side‐chain fluoropolymers. The long‐chain fluoropolymer formed in contrast to the tetrafluorosulfanyl (SF4) modified ones. The emulsions were applied on cotton fabrics to give hydrophobicity. The result showed that the fabrics treated with tetrafluorosulfanyl‐modified fluoropolymers were more hydrophobic, indicating that the introduction of SF4 was beneficial to provide lower surface energy and obtain better water repellent performance. The water contact angles record the varying degrees of variation in polymer degradation under UV exposure. The result showed that, as the perfluoroalkyl is bonded by SF4, when comparing with the carbon‐chain perfluoroalkyl polymer, the tetrafluorosulfanyl‐modified fluoropolymer is more degradable during UV irradiation.

Experimental Study on the Evaluation of Physical Performance and Durability of Cement Mortar Mixed with Water Repellent Impregnated Natural Zeolite.

To complement the shortcomings of concrete surface treatment technology and improve the durability of concrete structure, the purpose of this study was to impregnate water-repellent performance into natural zeolite, which has many pores inside, to achieve water-repellent performance inside concrete. The physical performance and durability of cement mortar mixed with water-repellent natural zeolite was evaluated. Cement mortars were prepared by mixing ZWR1%, 3%, and 5% (ZWR: Zeolite + Water Repellent impregnation) in cement powder, and compressive strength, contact angle, water penetration test, resistance chloride penetration test, chloride diffusion coefficient, and accelerated carbonation test were evaluated. When the mixing ratio of ZWR increased, the compressive strength of the test specimen was reduced compared to OPC. In contact angle measurement, water penetration test, chloride penetration resistance test, chloride diffusion coefficient, and accelerated carbonation test, the ZWR-containing samples showed superior properties compared to OPC. It was found that the durability test results improved as the amount of mixing was increased, and the durability of the test specimen containing 5% ZWR was found to be the best.

Effect of Morphology of Nano-Structured Surfaces on Anti-Icing Performance

Abstract Droplets bouncing off cold surfaces before being frozen is one way to achieve anti-icing, in which process superhydrophobic surfaces have been proven to play an important role. By using template-assisted method, three types of copper nanowired superhydrophobic surfaces (NSHSs) with mainly two morphologies (aggregated and upright) are fabricated. CuO nanograssed superhydrophobic surface (SHS) and copper smooth hydrophobic surface (HS) are also fabricated as a comparison. Compared with smooth HS and nanograssed SHS, all NSHSs exhibit better performance in repelling impacting droplet. In detail, on three types of NSHSs with temperatures ranging from 20 °C to −20 °C, impacting droplets can totally rebound. Among the three types, nanowires aggregated most exhibit the best water-repellency performance. The different performances among the five surfaces are due to surface temperature and surface morphology parameters, including micro/nano-size and surface roughness.

Anti-icing performance of hydrophobic material used for electromechanical drill applied in ice core drilling

AbstractUsing an anti-icing coating to prevent ice accretion on the drill surface is a feasible solution to address the drilling difficulties in warm ice. In this study, four types of commercially available hydrophobic coating materials were tested to evaluate their water repellency and anti-icing properties, namely, a mixture of silica and fluorocarbon resin with polytrifluoroethylene, modified Teflon, silica-based emulsion and an acrylic-based copolymer. Their water contact angles are ~107°, 101°, 114° and 95°, respectively. All these hydrophobic coatings can significantly reduce the strength of the ice adhesion within a temperature range of −10 to −30°C on a planar or curved surface. The coating of an acrylic-based copolymer, in particular, can reduce the average tensile strength and the shear strength of the ice adhesion by 87.08 and 97.11% on planar surfaces at −30°C, and by 98.06 and 96.15% on a curved surface, respectively. The main challenge in the practical application of these coatings is their durability. An acrylic-based copolymer coating will lose its water repellency performance after 140 cycles of abrasion. The shear strength of ice adhered on curved surfaces coated with this material will approach that achieved on uncoated surfaces after 11 cycles of icing and de-icing tests.

Bioresin-based superhydrophobic coatings with reduced bacterial adhesion

HypothesisCertain biobased polymers or natural compounds can be effectively used in superhydrophobic coating formulations to reduce environmental impact of fluorinated compounds and related bioaccumulation and toxicity problems. Many environmental concerns have thus far been raised in relation to toxicity of solvents and C8 fluorine chemicals. Elimination of these important elements from non-wettable coating formulations can jeopardize non-wetting performance significantly. However, intelligent and innovative approaches that introduce ecofriendly resins and compounds in superhydrophobic coating formulations without significantly altering self-cleaning superhydrophobicity are possible and being reported. ExperimentsSuperhydrophobic coatings based on a biomass-derived bioresin polyfurfuryl alcohol (PFA) were prepared. The coatings were made by blending PFA resin with a C6 perfluorinated acrylic copolymer PFAC in solution and subsequent spray coating. Silica nanoparticles were also added in order to repel some common oils. Coating morphology, chemical and thermal properties, biocompatibility and bacterial adhesion properties were studied in detail. FindingsCoatings having 50 wt% bioresin revealed equal water-repellency performance comapred to 100% PFAC-based coatings. Healthy cell growth was maintained on the coatings with no cell toxicity using human cell line, HeLa cells. Superhydrophobic coatings demonstrated very low bacterial adhesion to E. coli, S. aureus and Ps. aeruginosa indicating promising biofouling resistance. The coatings did not require any post thermal annealing. This would cause significant energy savings for large-scale adaptation.

Fabrication of durable superhydrophobic Mg alloy surface with water-repellent, temperature-resistant, and self-cleaning properties

Superhydrophobic surfaces have superiority in the manufacturing of engineered materials and have attracted considerable interest because of their water-resistant and self-cleaning properties. However, variations in temperature and complex environments limit their use particularly in self-cleaning windows, automobiles, and aircraft body panels. In this work, durable superhydrophobic surfaces were fabricated on a Mg alloy through an electrochemical etching method using NaCl and NaNO3. The contact angle of the superhydrophobic surface was up to 162.1°, and the sliding angle was only 3°. Interestingly, the surfaces were superhydrophobic and thus exhibited excellent water-repellent performance even when impacted by droplets or continuous water jet at a wide range of temperatures. Furthermore, the superhydrophobic surfaces have desirable temperature resistance, which is up to 260 °C owing to the thermal stability of the microstructures and the fluoroalkylsilane (FAS) film. Scanning electron microscopy (SEM) result demonstrates that the microstructures have good thermal stability, and X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectrometry (FTIR) confirm the stable FAS film. The prepared surfaces maintain exceptional self-cleaning properties after alternating-temperature treatment. This work presents a facile strategy for fabricating superhydrophobic surfaces with excellent water-repellent, temperature-resistant, and self-cleaning properties and demonstrates its great potential in practical applications.

Corncoblike, Superhydrophobic, and Phase-Changeable Nanofibers for Intelligent Thermoregulating and Water-Repellent Fabrics.

The comfort and protection of clothes are critically important for human well-being in life; however, constructing multifunctional fabrics with excellent thermoregulating and water-repellent performance still presents an exciting scientific challenge and a significant technological advancement. Therefore, we report a novel and straightforward methodology to fabricate corncoblike and phase-changeable nanofibers by incorporating n-octadecane phase change capsules (PCCs) for creating water-repellent and thermoregulating nanofibrous membranes. This strategy causes PCC to be uniformly distributed on the nanofibers to form a unique corncoblike structure, preventing the abscission of PCC and the leakage of the phase change ingredient (n-octadecane). Besides, the resultant nanofibrous membranes are endowed with hierarchical roughness, small pore size, and energy storage/release capacity in response to environmental changes. As a consequence, the nanofibrous membranes present prominent water repellence with superhydrophobicity (a water contact angle of 153°) and a high hydrostatic pressure of 84 kPa, robust mechanical properties with a tensile strength of 9.2 MPa, as well as excellent hybrid active-passive thermal regulation with a water vapor transmittance rate of 11.4 kg m-2 d-1 and a high phase change enthalpy of 74 J g-1 after 50 heating/cooling cycles, indicating them to be an exceptional candidate for personal protection and thermal management.

Investigation of sewing and water repellent performance of outdoor clothing

PurposeDurability of textile materials under wet conditions has become very important in recent years. The water repellency performance of fabrics should be maintained in the seam areas. The purpose of this paper is to analyze the effect of water repellent agents and sewing threads on the seam and water repellency performance properties of woven fabrics.Design/methodology/approach100 percent polyester woven fabrics were treated with three different water repellent finishing agents (silicone, fluorocarbons with 6 and 8 carbons) and then sewn with different sewing threads (unfinished/water repellent finished polyester/cotton corespun and polyamide filament). Afterwards, mechanical properties, seam performance and water repellency properties of these materials were measured.FindingsThe effect of finishing which was statistically significant on seam strength only in warp direction was significant on seam elongation and efficiency in both warp and weft directions. Seam strength, seam efficiency, seam slippage and seam pucker of fabrics sewn with polyamide threads were higher than others. The fluorocarbons applied to the fabrics gave higher water repellency values than silicones. In addition, as the chain length increased in fluorocarbons, water repellency performance increased. Sewing process reduced water resistance of fabrics; however, water repellent finish applied to the threads increased water resistance of fabrics.Originality/valueAs a result of the literature review, it was seen that water repellency property of a wear were studied in only seamless areas of fabrics. Originality of this study is that the water repellency properties are also analyzed in the seam areas of the fabrics and evaluated together with the seam performance characteristics.