Water-repellent Characteristics Research Articles

Optimised fluorine free polysiloxane based water repellent for cellulosic fabric

This research focuses on creating a new water-repellent finish for textiles utilising a sol-gel process and the combination of 3-glycidyloxypropyltrimethoxysilane (KH560) and gamma-Methacryloxypropyltrimethoxysilane (KH570) as a precursor which was then modified with branched silicone through sol-condensation. A fluorine-free, new-generation polysiloxane-based water repellent was prepared and analysed to achieve the best water repellent characteristics. Different parameters and conditions were tested during the preparation of chemicals to achieve this. After preparation, all the chemicals were characterised using various scientific analysing tools such as Fourier Transform Infrared radiation, thermogravimetric analysis, particle size analysis, contact angle and water-repellent testing. Following the particle size investigation, it was discovered that the particle size distributions for these samples were homogenous and advantageous, allowing for more efficient contact and penetration with the textile fibres. The results of this study confirm the existence of functional groups that can contribute to the desirable characteristics of the compounds to repel water with one coupling agent, KH570:KH560 = 0.02 mol:0.04 mol, showing particularly good water-repellence performance.

Self‐Assembly of 0D/3D Perovskite Bi‐Layer from a Micro‐Emulsion Ink

Abstract2D/3D bilayer perovskite synthesized using sequential deposition methods has shown effectiveness in enhancing the stability of perovskite solar devices. However, these approaches present several limitations such as uncontrolled chemical processes, disordered interfacial states, and microscale heterogeneities that can chemically, structurally, and electronically compromise the performance of solar modules. Here, this work demonstrates an emulsion‐based self‐assembly approach using natural lipid biomolecules in a nonionic solution system to form a 0D/3D bilayer structure. The new capping layer is composed of 0D‐entity nanoparticles of perovskite encapsulated by a hydrophobic lipid membrane, analogous to a cell structure, formed through a molecular self‐assembly process. This 0D layer provides a strong water repellent characteristics, optimum interface microstructure, and excellent homogeneity that drives significant enhancement in stability. Solar modules with a large active area of 70 cm2 fabricated using films comprising of 0D/3D bilayer structure are found to show consistent efficiency of >19% for 2800 h of continuous illumination in the air (60% relative humidity). This emulsion‐based self‐assembly approach is expected to have a transformative impact on the design and development of stable perovskite‐based devices.

Effect of Pore Size and Hydrophobic Coating on Oil-Water Separation System for Grease Trap

Public concern towards solidification of fat, oil, and grease (FOG) through disposed wastes into the drainage system is an unresolved issue to this day. The use of skimmer to separate oil and water form their mixture is a less comprehensive solution. This paper aimed to design the concept and fabricate oil-water separation medium, as well as to analyse the effect of different pore sizes of wire mesh and coating respectively. Water separation system is designed based on Pugh Method, while stainless steel wire mesh is used in analysing the water repellent and oil absorption characteristics. Titanium dioxide is used as coating. Surface characterization and contact angle of droplet were observed using scanning electron microscope and contact angle measurement tools. Hydrophobicity of uncoated stainless steel of wire mesh will increase if the pore size of wire mesh is decreasing in size. The more layers of coating increase the hydrophobicity of the wire mesh in increments with contact angle more than 100⁰. For the cooking oil droplet to expeditiously spread over the mesh surface and rapidly permeate through the mesh less than 1 second, showed the oleophilic nature of the mesh.

Water repellent characteristics of physical and biological crusts and their effects on water infiltration

Soil crust is a normal natural phenomenon with different water hydrophilicity and repellency due to different formation mechanism, thus affecting soil hydraulic characteristics and hydrological cycle. In this study, we measured water repellent characteristics of physical and biological crusts under different vegetations in the field using water drop penetration time (WDPT). The surface morphology of crusts was observed using scanning electron microscopy, and the infiltration characteristics of crusts and their non-crust soils (control) was evaluated with micro-infiltration device. The results showed that: 1) The average WDPT of physical crusts and the control soils was 3.3 s and 0.9 s, respectively, indicating that both were hydrophilic. The average WDPT of biological crusts ranged from 20.9 s to 140.9 s, which was 2.8 to 19 times that of control, and that under Diospyros lotus and Robinia pseudoacacia was 134.5 s and 140.9 s, respectively. 2) Compared with the control, the cumulative infiltration amount, average infiltration rate and moisture absorption force of physical crusts decreased by 0-4.3%, 3.5%-5.1%, and 27.2%-90.1%, respectively, while those of biological crusts decreased by 0-25%, 1.4%-28.2% and 36.0%-84.9%, respectively. 3) Regardless of the presence of crusts or not, there were "hockey-stick-like" curves by using Philip model to fit infiltration data. Before the WRCT point in the "hockey-stick-like" curve, the point source infiltration was mainly horizontal diffusion. After the WRCT point, the infiltration was mainly vertical diffusion. The presence of soil crust prolonged the formation time of the turning point. In all, physical crusts formed by inorganic mineral particles blocking the surface soil did not affect water repellency, while biological crusts that reflected the effects of hydrophobic organic compounds on soil structure enhanced its water repellency. Both physical crusts and biological crusts decreased the cumulative infiltration amount and average infiltration rate of soil. Compared with the control, physical crusts mainly affected soil hygroscopicity, but with limited effects on the steady infiltration rate. Biological crust decreased soil hygroscopicity and increased steady infiltration rate.

Achieving Superhydrophobic Surfaces via Air-Assisted Electrospray.

Superhydrophobic surface is an enabling technology in numerous emerging and practical applications such as self-cleaning, anticorrosion, antifouling, anti-icing coatings, and oil-water separation. Here, we report a facile air-assisted electrospray approach to achieve a superhydrophobic surface by systematically studying spray conditions and the chemistry of a coating precursor solution consisting of silicon dioxide nanoparticles, polyacrylonitrile, and N,N-dimethylformamide. The wettability behavior of the surface was analyzed with contact angle measurement and correlated with surface structures. The superhydrophobic coating exhibits remarkable water and oil repellent characteristics, as well as good robustness against abrasion and harsh chemical conditions. This air-assisted electrospray technique has shown great control over the coating process and properties and thus can be potentially used for various advanced industrial applications for self-cleaning and anticorrosion surfaces.

Water Repellency/Proof/Vapor Permeability Characteristics of Coated and Laminated Breathable Fabrics for Outdoor Clothing

This study examined the water repellency (WR), waterproof, and water vapor permeability (WVP) characteristics of twelve types of laminated and coated woven fabrics for outdoor clothing. These characteristics were compared with the fabric structural parameters, such as cover factor, thickness, and weight, and surface modification (finishing) factors, such as coating, laminating, and Teflon treatments. In addition, an eco-friendly process for surface modification was proposed followed by a summary. Superior waterproof-breathable characteristics with 100% water-repellency were achieved in specimen 3 in group A by treatment with a hydrophilic laminated finish using nylon woven fabric with a cover factor between 0.7 and 0.9 in a 2.5-layered fabric, which was the best specimen with waterproof-breathable characteristics. A high WVP in the coated and laminated fabrics was observed in the fabrics with a low weave density coefficient (WDC) and low thickness per unit weight of the fabric, whereas superior water repellency and waterproof characteristics were observed in the high-cover-factor (WDC) fabric with appropriate fabric thickness. The determination coefficient (R2) from regression analysis between the WVP and fabric structural parameters indicated a higher contribution of the fabric structural parameters than surface modification factors, such as coating and laminating to the WVP in the coated and laminated fabrics. Furthermore, the cover factor was the most important factor influencing the WVP of the waterproof-breathable fabrics. Of twelve coated and laminated fabrics, the laminated nylon and nylon/cotton composite fabrics showed superior WVP with high WR and waterproof characteristics. Accordingly, based on the WR, waterproof, and WVP characteristics of the coated and laminated breathable fabrics, the laminating method, as an eco-friendly process, is recommended to obtain better waterproof-breathable fabrics.

Water-Repellent Characteristics of Beech Wood Coated with Parylene-N.

In recent years, awareness regarding sustainability and the responsible usage of natural resources has become more important in our modern society. As a result, wood as a building material experiences a renaissance. However, depending on the use case, protective measures may be necessary to increase wood’s durability and prolong its service life. The chemical vapor deposition (CVD) of parylene-N layers offers an interesting alternative to solvent-based and potentially environmentally harmful coating processes. The CVD process utilized in this study generated transparent, uniform barrier layers and can be applied on an extensive range of substrates without the involvement of any solvents. In this study, European beech wood samples (Fagus sylvatica L.) were coated with parylene-N using the CVD process, with paracyclophane as a precursor. The aim of the study was to analyze the water absorption of beech wood, in relation to the different layer thicknesses of parylene-N. Therefore, four different coating thicknesses from 0.5 to 40 μm were deposited, depending on the initial amount of precursor used. The deposited layers were analyzed by reflection interference spectroscopy and scanning electron microscopy, and their chemical structures and compositions were investigated by X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Due to the chemical structure of parylene-N, the deposited layers led to a significantly increased water contact angle and reduced the water uptake by 25–34% compared to the uncoated reference samples. A linear correlation between layer thickness and water absorption was observed. The coating of wood with parylene-N provides a promising water barrier, even with thin layers.

How to protect agricultural workers from exposure to pesticides: Effectiveness of woven and natural resin-coated fabrics

Agricultural workers in low and middle-income countries usually wear their everyday clothing made of woven fabrics during pesticide application. Different characteristics of various woven fabrics have different abilities to prevent the penetration of pesticides through to the skin. Therefore, the ultimate goal of this study is that agricultural workers in Thailand can choose a suitable fabric of protective clothing to protect themselves from pesticide exposure. This study aims to investigate pesticide penetration levels in different woven fabrics, and to explore factors affecting levels of pesticide penetration through fabrics. In addition, our study aims to produce cotton fabrics coated with a natural resin to obtain water-repellent characteristics and evaluate their effectiveness in protecting against pesticides. Four pesticides used in the testing process were chlorpyrifos, cypermethrin, paraquat, and glyphosate. The results found that a suitable fabric to protect agricultural workers from pesticide exposure is a fabric which made of 100% cotton and have greater weight. With regard to natural resin-coated fabrics, fabric C1-R showed the highest levels of effectiveness in protecting against the pesticides (range between 89%-95%). The natural resin-coated fabric is an alternative fabric in the protection against pesticides for agricultural workers in low and middle-income countries when commercial PPE are prohibitively expensive.

Water repellency in eucalyptus and pine plantation forest soils and its relation to groundwater levels estimated with multi-temporal modeling

Abstract Water repellency makes soils capable of resisting to the penetration of water applied on the surface and inflict various influences on groundwater. The objectives of the present study were to identify the water repellency under pine and eucalyptus plantations, to determine social impacts of water level changes, to find possible changes in groundwater levels in the surrounding areas during the past four decades, and to relate water repellent characteristics of soils with the groundwater level changes. The study was conducted in eucalyptus (Eucalyptus grandis) and pine (Pinus caribaea) plantation forests located in Upcountry intermediate zone, Sri Lanka. Each land was separated into three blocks (B1, B2, B3) based on the slope. Water repellency was measured with water drop penetration time (WDPT) and contact angle. The water entry value was estimated with the pressure head method. Interconnected social impacts was examined using a questionnaire based survey. Groundwater levels from 1980 to present were modeled with remotely sensed information. Both eucalyptus and pine forest soils showed water repellency, which decreased with increasing soil depth. Eucalyptus soils showed highly hydrophobic conditions on the surface (WDPT>7200 s). Ponding depths required for entry of water into the soil in eucalyptus soils was 4.6–5.3 cm, whereas that of pine soils was 1.5–4.0 cm, although achieving these levels would be difficult considering the steep slopes. Contact angle showed positive logarithmic correlation with water entry value. The people living in the surrounding areas expressed less water availability for their domestic purposes, decreased water level in household wells, and drying up of natural water resources at present compared with 1980s. Modelling with remotely sensed thematic maps confirmed that the groundwater levels in both areas has decreased over the time. It indicated that the eucalyptus and pine vegetation have created unfavorable conditions in regard with water entry and groundwater recharge. Proper attention from the responsible authorities will be essential to prevent the adverse impacts of on groundwater resources.

Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof

We investigate wetting and water repellency characteristics of Colocasia esculenta (taro) leaf and an engineered surface, bioinspired by the morphology of the surface of the leaf. Scanning electron microscopic images of the leaf surface reveal a two-tier honeycomb-like microstructures, as compared to previously-reported two-tier micropillars on a Nelumbo nucifera (lotus) leaf. We measured static, advancing, and receding angle on the taro leaf and these values are around 10% lesser than those for the lotus leaf. Using standard photolithography techniques, we manufactured bioinspired surfaces with hexagonal cavities of different sizes. The ratio of inner to the outer radius of the circumscribed circle to the hexagon (b/a) was varied. We found that the measured static contact angle on the bioinspired surface varies with b/a and this variation is consistent with a free-energy based model for a droplet in Cassie-Baxter state. The static contact angle on the bioinspired surface is closer to that for the leaf for b/a ≈ 1. However, the contact angle hysteresis is much larger on these surfaces as compared to that on the leaf and the droplet sticks to the surfaces. We explain this behavior using a first-order model based on force balance on the contact line. Finally, the droplet impact dynamics was recorded on the leaf and different bioinspired surfaces. The droplets bounce on the leaf beyond a critical Weber number (We ~ 1.1), exhibiting remarkable water-repellency characteristics. However, the droplet sticks to the bioinspired surfaces in all cases of We. At larger We, we recorded droplet breakup on the surface with larger b/a and droplet assumes full or partial Wenzel state. The breakup is found to be a function of We and b/a and the measured angles in full Wenzel state are closer to the predictions of the free-energy based model. The sticky bioinspired surfaces are potentially useful in applications such as water-harvesting.

Sol–gel finishing of bamboo fabric with nanoparticles for water repellency, soil release and UV resistant characteristics

This research work reports on the preparation of a durable hydrophobic bamboo knitted fabric with multifunctional properties using sol–gel coating method. The titania nanoparticles (TNPs) and silica nanoparticles (SNPs) composite sols were made using citric acid as cross-linking agent. The bamboo knitted fabric was functionalized by the dip-pad-dry-pad-cure method. Different ratios of TNPs and SNPs were made. All process and solution parameters of sol–gel coating method were optimized to achieve the desired fabric properties. ATR-FTIR spectroscopy, EDS and SEM analysis were carried out to characterize the untreated and sol–gel coated bamboo knitted fabrics. The hydrophobicity, soil release, UV resistance and wash-durability of bamboo knitted fabrics functionalized with NPs (nanoparticles) were measured. The results revealed that the sol–gel coating of TNPs and SNPs on bamboo fabric was durable up to five industrial washes. Moreover, air permeability and fabric handle did not change after sol–gel finishing indicating that the fabric inherent comfort remained unaffected.

Icephobic performance of superhydrophobic coatings: A numerical analysis

Understanding the mechanism of cloud-sized particles impact and freezing is crucial to find viable solutions to prevent ice accumulation on critical aerodynamic surfaces such as aircraft wing or nacelle. It has been reported that superhydrophobic surfaces (SHS) have promising anti-icing properties due to their excellent water-repellent characteristics. However, due to the complexity of the freezing phenomenon on superhydrophobic surfaces, the anti-icing performance of such surfaces has not been fully understood. A multi-region multiphase flow solver including phase change has been developed to model the icing of a micro-droplet as it impinges on a superhydrophobic substrate with a given thickness, texture, and solid material thermal properties. The Navier-Stokes equation expressing the flow distribution of the liquid and the gas, coupled with the volume of fluid (VOF) method for tracking the liquid-gas and liquid-solid interfaces, was solved numerically using the finite volume methodology. The superhydrophobic morphology is modeled through a series of micro-structured arrays with squared cross-sectional pillars. As such, the thermal contact resistance is inherently accounted by the inclusion of air pockets underneath the micro-droplet. Consequently, the direct effect of surface topology and thermal properties on droplet maximum spreading diameter, penetration to the surface asperities, contact time, and the freezing onset have been investigated. Finally, icephobicity of two similar SHSs with various thermal properties were compared.

Tunable Multimodal Drop Bouncing Dynamics and Anti-Icing Performance of a Magnetically Responsive Hair Array.

Anti-icing materials that can efficiently limit ice formation have a strong potential to replace existing anti-icing techniques, such as Joule heating, chemical release, or mechanical removal, which are usually inefficient, expensive, and environmentally harmful. In this study, an anti-icing material based on a magnetically responsive hierarchical hair array that can actively modulate drop bouncing dynamics is presented. The magnetically responsive hair array exhibits an immediate and reversible structural bending motion in response to an external magnetic field. The array also exhibits superhydrophobicity, regardless of its tilt angle, due to the tapered geometry of the hairs and the multiscale surface roughness of the array. Due to its dynamic structure and water-repellent characteristics, the array can induce distinct multiple modes of drop bouncing behavior by adjusting its structural bending state in a reversible fashion. Three different types of bouncing behavior, namely, quasi-pancake bouncing, directional bouncing, and macrotexture-induced droplet fragmentation, can be obtained with the vertical, tilted, and fully bent hair arrays, respectively. We demonstrate that the dynamically controllable drop bouncing behavior of the magnetically responsive hierarchical array enables the efficient and robust prevention of ice formation and accumulation.

Hydrophobicity performance of polyethylene terephthalate (PET) and thermoplastic polyurethane (TPU) with thermal effect

Combining the flexibility and stretchability of printed flexible circuits (PFC) such as PET and TPU with water repellent characteristics may improve the functionality of printed circuit for electronic packaging. Water repellent characteristics using ceramic-based coating may protect the surface from degradation and moisture absorption due to the hydrophobicity behavior of the surface after coating. This paper seeks to provide insight into characterization and understanding on the effect of thermal on the hydrophobic performance of polymer substrate (PET and TPU) with and without coated with a ceramic coating which is Titanium Dioxide (TiO2) for more robust and vigorous hydrophobic coating. The annealing temperature was determined by using DSC analysis and four different temperatures have been used in this study. Contact angle and surface roughness characterization were evaluated by self-fabricate contact angle measurement tools and Mitutoyo Profilometer Surftest SJ410. The results reveal that hydrophobicity of uncoated TPU increase and PET decrease after thermally aged. However, after coated with TiO2, both substrate shows further increment in hydrophobicity with contact angle more than 90˚. The 2D profile reveals that surface roughness protrusion becomes one of the factors affecting the hydrophobicity of the surface due to liquid-air interfaces under the droplet (air trap) as stated in Wenzel and Cassie-Baxter theory.

撥水材を混入したセメント系材料の内部撥水性と材料特性の検討

コンクリートへの水分浸透の抑制手法として表面含浸工法などがあるが，ひび割れが生じると抑制が困難となる。そこで，本研究では，撥水材をセメントペーストに直接混入，もしくは105℃で絶乾した細骨材に噴霧することで，構成材料として内部に加え，ひび割れ発生後も内部から撥水性を保持できるセメント系材料の作製を検討した。その結果，市販のシリコーン系撥水材を噴霧した細骨材を用いたモルタルは，表面撥水性を発揮し，圧縮強度は最大で50%程度低下するものの，ひび割れを有しても水分浸透が抑制された。さらに，アルキル変性シロキサンポリマーを主成分とするシリコーン系撥水材を用いると，乾燥後の吸水，乾燥収縮が3か月にわたって抑制できた。

Postfire soil water repellency in piñon-juniper woodlands: Extent, severity, and thickness relative to ecological site characteristics and climate.

Wildfires can create or intensify water repellency in soil, limiting the soil's capacity to wet and retain water. The objective of this research was to quantify soil water repellency characteristics within burned piñon–juniper woodlands and relate this information to ecological site characteristics. We sampled soil water repellency across forty‐one 1,000 m2 study plots within three major wildfires that burned in piñon–juniper woodlands. Water repellency was found to be extensive—present at 37% of the total points sampled—and strongly related to piñon–juniper canopy cover. Models developed for predicting SWR extent and severity had R 2 adj values of 0.67 and 0.61, respectively; both models included piñon–juniper canopy cover and relative humidity the month before the fire as coefficient terms. These results are important as they suggest that postfire water repellency will increase in the coming years as infilling processes enhance piñon–juniper canopy cover. Furthermore, reductions in relative humidity brought about by a changing climate have the potential to link additively with infilling processes to increase the frequency and intensity of wildfires and produce stronger water repellency over a greater spatial extent. In working through these challenges, land managers can apply the predictive models developed in this study to prioritize fuel control and postfire restoration treatments.

Scalable super-hydrophilic nanocomposite latex with self-cleaning action

Abstract Super-hydrophilic polyacrylate nanocomposite latex was prepared by emulsion polymerization of methyl methacrylate (MMA) and butyl acrylate (BA) with modified nano-silica and hydrogenated tallow montmorillonite (MMT) clay. Modification of nanoparticles were carried out using vinyl trimethoxysilane (VTMS) coupling agent. The nanoparticle loading was maintained constant at 0.5% of total formulation while changing the ratio of nano-silica to nano-clay. The modification of the nanoparticles were investigated using particle size and SEM analysis. The coating properties were studied on three different substrates, asbestos, glass and mild steel. The water repellent characteristics of the film and mechanical performance of the coatings were established and compared to the coating with zero nanoparticles taken as reference standard.

Superhydrophobic coatings for aluminium surfaces synthesized by chemical etching process

ABSTRACTIn this paper, the superhydrophobic coatings on aluminium surfaces were prepared by two-step (chemical etching followed by coating) and one-step (chemical etching and coating in a single step) processes using potassium hydroxide and lauric acid. Besides, surface immersion time in solutions was varied in both processes. Wettability and surface morphologies of treated aluminium surfaces were characterized using contact angle measurement technique and scanning electron microscopy, respectively. Microstructures are formed on the treated aluminium surfaces which lead to increase in contact angle of the surface (>150°). Also on increasing immersion time, contact angle further increases due to increase in size and depth of microstructures. Additionally, these superhydrophobic coatings show excellent self-cleaning and corrosion-resistant behavior. Water jet impact, floatation on water surface, and low temperature condensation tests assert the excellent water-repellent nature of coatings. Further, coatings are to be found mechanically, thermally, and ultraviolet stable. Along with, these coatings are found to be excellent regeneration ability as verified experimentally. Although aforesaid both processes generate durable and regenerable superhydrophobic aluminium surfaces with excellent self-cleaning, corrosion-resistant, and water-repellent characteristics, but one-step process is proved more efficient and less time consuming than two-step process and promises to produce superhydrophobic coatings for industrial applications.

An Ultrahydrophobic Fluorous Metal-Organic Framework Derived Recyclable Composite as a Promising Platform to Tackle Marine Oil Spills.

Derived from a strategically chosen hexafluorinated dicarboxylate linker aimed at the designed synthesis of a superhydrophobic metal-organic framework (MOF), the fluorine-rich nanospace of a water-stable MOF (UHMOF-100) exhibits excellent water-repellent features. It registered the highest water contact angle (≈176°) in the MOF domain, marking the first example of an ultrahydrophobic MOF. Various experimental and theoretical studies reinforce its distinctive water-repellent characteristics, and the conjugation of superoleophilicity and unparalleled hydrophobicity of a MOF material has been coherently exploited to achieve real-time oil/water separation in recyclable membrane form, with significant absorption capacity performance. This is also the first report of an oil/water separating fluorinated ultrahydrophobic MOF-based membrane material, with potential promise for tackling marine oil spillages.

Variable wettability control of a polymer surface by selective ultrasonic imprinting and hydrophobic coating

Surface wettability is the ability of a liquid to maintain contact with a solid surface, and there have been many studies aimed at controlling surface wettability for development of functional surfaces. In this study, an approach to control surface wettability is proposed by differentiating surface energy of polycarbonate in specified regions, using a combination of two surface treatments: (i) micropattern replication using selective ultrasonic imprinting and (ii) hydrophobic coating using organic silane. In both treatments, profiled masks were used to reduce surface energy in target regions where semi-hydrophobic polycarbonate surfaces were changed to hydrophobic states. Various combinations of selective ultrasonic imprinting and hydrophobic coating were investigated in terms of changes in surface wettability, by measuring contact angle (CA) behaviors on the developed surfaces. By controlling such changes, the surface wettability of regions on a single polycarbonate surface could be differentiated, allowing semi-hydrophobic (CA 87.8°), hydrophobic (CA 114.8°) and superhydrophobic (CA 155.6°) states to coexist. This high CA difference (>60°) on a single surface was then applied to enhance water-repellent characteristics so that the surface wettability could be controlled effectively. Mechanical durability of the developed hybrid surface was also discussed by investigating its CA behavior after surface abrasion.