The wettability of industrial surfaces: Contact angle measurements and thermodynamic analysis

The water wettability of surfaces, whose surface conditions are comparable to those used in heat and mass transfer equipment, has been investigated experimentally and theoretically.In the first part, results of contact angle measurements for water on metal and non-metal surfaces are reported. With hydrophobic non-metal surfaces (e.g. Teflon) water forms large advancing and receding contact angles, and the contact angle hysteresis is small. Surface contamination is of minor influence. Hydrophilic metal surfaces (copper, nickel) are completely wetted by water only if the surfaces are extremely clean. Surface contamination reduces the wettability drastically. Under most industrial conditions advancing contact angles between 40° and 80°, and receding contact angles smaller than 20° can be expected, and the contact angle hysteresis is large. Corrosion can enhance the water wettability.In the second part, a thermodynamic analysis of the wetting of heterogeneous surfaces is presented. Equilibrium considerations for a model surface consisting of two components of different wettability provide the advancing and receding contact angles for a heterogeneous surface as a function of the equilibrium contact angles, surface fractions, and the distribution function of the two components. The advancing and receding contact angles as well as all the intermediate contact angles indicate metastable states of equilibrium of the system. The results of the model calculations give a physically based explanation for the characteristic wetting behaviour of industrial surfaces found experimentally.     

Control over wettability of textured surfaces by electrospray deposition

Microtextured surfaces were prepared by electrospray deposition (ESD) from hydrophilic and hydrophobic acrylic resin solutions. The surface morphologies and topologies were characterized using scanning electron microscopy and laser profile microscopy, respectively. Wetting behaviors on the surfaces were characterized by contact angle and sliding angle measurements. The contact angle of the water droplet on the hydrophilic resin‐coated surfaces decreased with an increase in the surface roughness. On the other hand, the contact angle on the hydrophobic resin‐coated surfaces increased with an increase in the surface roughness. In addition, a patterned surface composed of aligned fibers by ESD showed anisotropy of both wetting and sliding behaviors. These results indicate that ESD is a useful method for designing a textured surfaces and controlling the surface wettability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3811–3817, 2007     

Pool boiling fouling and corrosion properties on liquid‐phase‐deposition TiO2 coatings with copper substrate

Fouling on the heat transfer surfaces of industrial heat exchangers is an intractable problem, and several techniques have been suggested to inhibit fouling. Surface coatings are of such techniques by which the adhesion force between fouling and heat transfer surface can be reduced with low surface free energy thin films. In this article, liquid phase deposition was applied to coat titanium dioxide thin films on the red copper substrates with film thickness in micro‐ or nano‐meter scale. Coating thickness, contact angle, roughness, surface topography, and components were measured with X‐ray diffraction, contact angle analyzer, stylus roughmeter, scanning electron microscopy, and energy dispersive X‐ray spectroscopy, respectively. Surface free energy of coating layers was calculated based on the contact angle. Heat transfer and fouling characteristics in pool boiling of distilled water and calcium carbonate solution on coated surfaces were investigated. Heat transfer enhancement was observed on coated surfaces compared with untreated or polished surfaces due to the micro‐ and nano‐structured surfaces which may increase the number of nucleation sites. The nonfouling time on the coated surfaces is extended than that on the untreated or polished surfaces due to the reducing of the surface free energy of coated surfaces. Corrosion behavior of coated surfaces soaked in the corrosive media of hydrochloric acid, sodium hydroxide alkali, and sodium chloride salt solutions with high concentration at room temperature a few hours was also explored qualitatively. Anticorrosion results of the coated surfaces were obtained. The coatings resisted alkali corrosion within 7.2 × 10⁵ s, acidic corrosion within 3.6 × 10⁵ s and salt corrosion within 2.16 × 10⁶ s. The present work may open a new coating route to avoid fouling deposition and corrosion on the heat transfer surfaces of industry evaporators, which is very important for energy saving in the related industries. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Novel water and oil repellent POSS-based organic/inorganic nanomaterial: Preparation, characterization and application to cotton fabrics

A series of polyhedral oligomeric silsesquioxane (POSS) based hybrid terpolymers P(POSS-MMA-(HFPO)₃MA) were synthesized and characterized by NMR, FT-IR, GPC, DSC and TG. The thermal properties of these terpolymers were improved by the introduction of POSS cage. The cotton fabrics coated with these terpolymers possessed excellent water and oil repellency. The water and salad oil contact angle could be achieved from ∼140° to 152° and from ∼127° to 144° respectively as the content of POSS in the terpolymer increased from 6.4 wt% to 13.4 wt%. Compared with P(MMA-(HFPO)₃MA) copolymer-coated cotton fabrics, POSS-based terpolymer coated cotton fabrics showed better oil repellency with a tendency of first increasing and then decreasing with an increase of the POSS content. The n-hexadecane (surface tension: 27.4 mN/m, 20 °C) contact angle reached ∼117° for coated cotton fabrics with terpolymer containing 9.5 wt% of POSS.     

Modification of cellulose fabrics with reactive polyhedral oligomeric silsesquioxanes to improve their shape‐memory performance

Reactive polyhedral oligomeric silsesquioxane (R‐POSS) containing multi‐N‐methylol is a functional and attractive staring monomer for new reinforcement materials. R‐POSS has excellent potential as a nanosized core for starburst dendrimers and highly reactive multi‐N‐methylol. R‐POSS can be used for cellulose fabric finishing to improve its shape‐memory performance. Factors affecting the crosslinking reaction of the cellulose with R‐POSS were investigated. The physical properties and morphological structure of the cellulose fabrics modified with R‐POSS are discussed with respect to the crease recovery angle, the whiteness index, micro‐Fourier transform infrared spectroscopy, and scanning electron microscopy. The results show that the crease recovery angle of the fabric modified with R‐POSS obviously increased. With increasing R‐POSS concentration, the crease recovery angle of the modified fabric sharply increased. R‐POSS readily crosslinked to cellulose and improved the elastic recovery of the cellulose fabrics. The surfaces of the cellulose fibers modified with R‐POSS were smooth and full. The inclusion of R‐POSS with dimethylol dihydroxyl ethylene urea to modify the cellulose showed very interesting results. It showed a good combination of an increase of crease recovery angle and a decrease in tensile strength. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Antimicrobial polyethylene terephthalate (PET) treated with an aromatic N‐halamine precursor,m‐aramid

A commercial m‐aramid as N‐halamine precursor has been coated onto polyethylene terephthalate (PET) fabric surface by pad‐dry‐curing process. The process is accomplished by padding the scoured PET fabric through the homogeneous m‐aramid solution, drying at 150°C for 3 min, and curing at 230°C for 3 min. The PET surface coated with m‐aramid was characterized using fourier transform infrared‐attenuated total reflection (FTIR‐ATR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). FTIR exhibits new bands in the 1645 and 1524 cm^?1 regions as characteristic of m‐aramid bands, which indicate the PET fabric coated with m‐aramid. XPS results show a distinguishable peak at binding energy 398.7 eV, which confirms the nitrogen atom of m‐aramid on the PET surface. In addition, SEM image shows a layer of coating onto the PET surfaces, which demonstrates the presence of m‐aramid coating on the surface of the PET. After exposure to dilute sodium hypochlorite solution, exhibition of antimicrobial activity on the coated PET is attributed to the conversion of N‐halamine moieties from the N‐halamine precursor. The chlorinated PET showed high antimicrobial activity against Gram‐negative and Gram‐positive bacteria. The chlorinated PET coated with 10% m‐aramid exhibited about 6 log reductions of S. aureus and E. coli O157:H7 at a contact time of 10 and 30 min, respectively. Furthermore, the antimicrobial activity was durable and rechargeable after 25 wash cycles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrophobic cotton fabric coated by a thin nanoparticulate plasma film

The audio frequency (AC) plasma of some kind of fluorocarbon chemical was applied to deposit a nanoparticulate hydrophobic film onto a cotton fabric surface. The measurement of the video contact angle showed that the superhydrophobicity of the cotton fabric was obtained with a treatment of only 30 s. The softness, water retention, moisture regain, color retention, abrasion, friction, and permeability were thoroughly investigated by a standard method that compared the fabric with a commercial Scotchgard‐protector‐sprayed cotton fabric. The results showed that the textile performances of the plasma‐coated fabric were superior to those of Scotchgard‐sprayed samples, except for the moisture regain, which was almost the same. A post‐treatment at a high temperature was conducive to increasing the hydrophobicity and the recovery of the water repellency of the plasma‐coated fabric after it was washed. Atomic force microscopy images and time‐of‐flight secondary‐ion mass spectra of plasma thin films on silicon wafers indicated that some physical and chemical changes took place during the post‐treatment process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1473–1481, 2003     

Adsorption of polyethylene from solution onto starch film surfaces

We prepared starch films by jet‐cooking aqueous dispersions of high‐amylose starch and then allowing the jet‐cooked dispersions to air‐dry on Teflon surfaces. When the starch films were immersed in 1% solutions of polyethylene (PE) in 1‐dodecanol, dodecane, and xylene at 120°C and the solutions were allowed to slowly cool, PE precipitated from the solutions and adsorbed onto the starch film surfaces. Fourier transform infrared spectroscopy was used to estimate the micrograms of PE adsorbed per square centimeter of starch film. PE was preferentially adsorbed onto the film side that was in contact with the Teflon surface during drying. The amount of PE adsorbed ranged from about 8 to 45 μg/cm² and depended upon the solvent used and the final temperature of the cooled solution. Scanning electron microscopy of the starch film surfaces showed discontinuous networks of adsorbed PE on the Teflon side and widely spaced nodules of adsorbed PE on the air side. NMR analysis showed that the PE adsorbed onto the starch surface was more linear and/or had a higher molecular weight than the starting PE. Possible reasons for the selective adsorption of PE onto the Teflon side of the starch film surface are discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

POSS/有机硅改性聚丙烯酸酯无氟防水剂的合成与应用研究

通过无皂乳液聚合技术合成了POSS/有机硅改性聚丙烯酸酯无氟防水剂,并将其应用于棉织物整理。考察了软硬单体配比对乳液、乳胶膜及其应用性能的影响。利用傅里叶红外光谱(FT-IR)和傅里叶红外光谱(DLS)对聚丙烯酸酯的结构及乳胶粒的粒径大小进行了表征,利用伺服材料多功能高低温控制试验机、柔软度仪、SEM对整理织物的应用性能及表面形貌进行了表征。结果表明：当m(BA):m(MMA)为6:4时,单体的转化率最大为96.97%,乳液的凝胶率为0.14%,乳胶粒的粒径最小为104.8 nm,乳胶膜对水的接触角最大可达114.3?,并具有优异的耐水性。整理棉织物表现出优异的力学性能和良好的柔软度,其对水的接触角可达161?。SEM结果表明棉织物纤维表面存在功能化POSS纳米颗粒。无氟防水剂赋予棉织物纤维表面低的的表面能和一定的粗糙结构,从而使整理棉织物表现出超疏水性能。     

Acrylic polyester resins containing perfluoropolyethers structures: Synthesis,characterization, and photopolymerization

Poly(ε‐caprolactone‐b‐perfluoropolyether‐b‐εcaprolactone) (PCL–PFPE–PCL) block copolymers having different PCL block lengths and end‐capped with methacrylate groups were prepared and characterized. Spectroscopic analyses confirmed the expected molecular structure of the products. After UV curing, the films revealed the presence of two amorphous phases, corresponding to fluorinated and hydrogenated moieties, respectively. The material containing long PCL blocks showed also a crystalline phase. Surface properties of the UV‐cured films were evaluated: The surfaces have a very high hydrophobic character in spite of the presence of many polar OH groups present in the polymeric network and a high hysteresis in wetting. An enrichment of fluorine at the air‐side surface was shown by contact‐angle measurements, except when long PCL sequences are present. The θ_adv angles decreased by increasing the content of PCL, that is, by decreasing the content of fluorine. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 651–659, 2000     

Layer‐by‐layer assembly of halogen‐free polymeric materials on nylon/cotton blend for flame retardant applications

Thin films of environmentally safe, halogen free, anionic sodium phosphate and cationic polysiloxanes were deposited on a Nyco (1:1 nylon/cotton blend) fabric via layer‐by‐layer (LbL) assembly to reduce the inherent flammability of Nyco fabric. In the coating process, we used three different polysiloxane materials containing different amine groups including, 35–45% (trimethylammoniummethylphenythyl)‐methyl siloxane‐55‐65% dimethyl siloxane copolymer chloride salt (QMS‐435), aminoethylaminopropyl silsesquioxane‐methylsilsesquioxane copolymer oligomer (WSA‐7021) and aminopropyl silesquioxane oligomers (WSA‐991), as a positive polyelectrolyte. Thermo‐gravimetric analysis showed that coated fabric has char yield around 40% at 600 °C whereas control fabric was completely consumed. The vertical flame test (VFT) on the LbL‐coated Nyco fabric was passed with after flame time, 2 s, and the char length of 3.81 cm. Volatile and nontoxic degradation products of flame retardant‐coated fabric were analyzed by pyrolysis gas chromatography mass spectroscopy (Py‐GCMS). Surface morphology of coated fabrics and burned fabric residues were studied by scanning electron microscopy. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface modification of silicone rubber with poly(ethylene glycol) hydrogel coatings

Hydrogel coatings of monoacrylated poly(ethylene glycol) (PEG) methyl ethers of different molecular weights were attached to silicon rubber surfaces and crosslinked with hexanediol diacrylate or ethoxylated trimethylolpropane diacrylate by UV polymerization. The wetting, evaluated with the water contact angles, correlated with the surface oxyethylene chain density, which was evaluated with the ESCA >C? O? /? CH₂? ratio obtained from the C(1s) peak. As measured by the ESCA N(1s) peak, bovine serum albumin formed very thin protein adsorbates on the PEG‐coated surfaces. A strong correlation was found between low protein adsorption and a high >C? O? /? CH₂? ratio of the PEG‐coated substrate. The PEG‐coated silicon rubber also demonstrated very low cell and platelet adhesion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1486–1492, 2004     

Ultrafiltration Membranes Coated by Amphiphilic Copolymers Containing Superhydrophilic Zwitterionic and Hydrophobic POSS Moieties Showing Improved Fouling Resistance/Release Properties

Ultrafiltration membranes coated with amphiphilic copolymers containing superhydrophilic zwitterionic moieties and hydrophobic POSS moieties (PSM‐coated membranes) are prepared. The free radical polymerization of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and 3‐(3,5,7,9,11,13,15‐heptaisobutylpentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]octasiloxane‐1‐yl)propyl methacrylate (MAPOSS) monomers is used to prepare a series of copolymers containing different compositions of DMAEMA and MAPOSS units (PDMs). The DMAEMA units in the PDM‐coated membranes are subsequently converted to sulfobetaine methacrylate (SBMA) units using 1,3‐propane sultone (post‐zwitterionization) to give the PSM‐coated membranes. The PSM‐coated membranes show improved fouling resistance/release properties, compared with a neat polysulfone (PSf) membrane. The improved fouling resistance properties of the PSM‐coated membranes are attributed to the superhydrophilic zwitterionic moieties, which form a hydration layer on the membrane surface via electrostatic interactions between the zwitterions and water molecules. Moreover, the total surface energy (γ_S) value of the PSM‐coated membrane is smaller than that of the PSf membrane due to the hydrophobic POSS moieties. This results in the superior fouling release properties of the PSM‐coated membranes.     

Imparting conductivity and chromic behavior on polyester fibers by means of poly(3‐methylthiophene) nanocoating

Poly(3‐methylthiophene) (P3MT)‐coated polyester fabric is a conductive textile with specific electrical and optical properties; for instance, color change under external stimulus (chromic behavior) was successfully prepared by chemical polymerization with continuous, speed stirring technique. To investigate the striking effect of some variable conditions of polymerization process, the effect of reaction time, temperature, and oxidant concentration on conductivity of the P3MT‐coated fabric was studied. Scanning electron microscopy confirmed that the surface of fabric has entirely been coated with P3MT particles. The further characterizations were investigated using Fourier transform infrared spectroscopy to provide evidence of forming particles onto the fabric, UV–vis absorption spectroscopy, electrical surface resistivity, and pressure dependence visible reflectance spectrophotometer measurements and X‐ray diffraction analysis. The blue shift in wavelength of maximum absorption of about 95 nm to a longer wavelength from that observed in the reflectance spectra of coated polyester fabric; under high‐pressure P3MT‐coated polyester fabric demonstrated piezochromism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of superhydrophobic wood surfaces

Superhydrophobic films were developed on wood substrates with a wet chemical approach. Growth of zinc oxide (ZnO) nanorods was found differentially in the cross‐sectional walls and inner lumenal surfaces. The surface roughness of the prepared films on the inner lumenal surface conformed to the Cassie–Baxter wetting model, whereas the roughness across the microsurface of the cell wall was in conformity with the hydrophobic porous wetting model. The space between the ZnO nanorods and the microstructure of the wood surface constituted the nanoscale and microscale roughness of the ZnO nanofilm, respectively. The water contact angle of the prepared wood surfaces was up to 153.5°. In the prepared films, monolayers of stearic acid molecules were self‐assembled on the ZnO nanorods, which in turn, were attached to the wood surface via dimeric bonds. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparison of drag characteristics of self-polishing co-polymers and silicone foul release coatings: A study of wettability and surface roughness

An experimental study has been carried out to evaluate the drag characteristics of different self-polishing co-polymers (SPC) (tin based and tin-free) and a silicone foul release (FR) coating. Drag measurements have been performed on a smooth aluminum cylinder connected to a rotor device. Various coatings on cylinders were examined and differential length technique was also used to avoid the end effects during rotation. Surface energy of the coated samples was determined using static contact angle measurement. Characteristic roughness measurements of the coated surfaces were evaluated with atomic force microscopy (AFM) technique.Drag measurements showed that the frictional resistance of the FR coated cylinders was lower than that of SPC coated samples.Contact angle results showed that the critical surface tension and its polar component for silicone FR coating are less than SPC coatings. This prevents firm adhesion of fouling organisms on underwater hulls.AFM studies revealed a lower surface roughness for silicone FR coating as compared to SPC coatings. Also, its surface texture is considerably different from SPC coatings.It can be concluded that the drag characteristics of a surface are affected by its free energy and roughness parameters.     

Contact Angle of Ethanol and n‐Propanol Aqueous Solutions on Metal Surfaces

The contact angles of the aqueous solution of ethanol and that of n‐propanol on copper, aluminum, and stainless steel surfaces are reported. The contact angles were measured under atmospheric conditions, and then under vapor‐liquid equilibrium conditions at 1 atm and different temperatures. The results showed the variations of the contact angles with the concentrations of aqueous solutions on different metal material surfaces with different roughness. Some unstable behavior of the wetting ability around the azeotropic point of a binary solution is reported. Influences of concentration, kind of materials, and the surface roughness on the wetting ability are discussed. The model for predicting the contact angle of alcohol aqueous solutions on metal surfaces under atmospheric and vapor‐liquid two‐phase equilibrium conditions at 1 atm is derived from the Young equation.     

Toward efficient water/oil separation material: Effect of copolymer composition on pH‐responsive wettability and separation performance

Interest in functional soft matter with stimuli‐responsive wettability has increasingly intensified in recent years. From the chemical product engineering viewpoint, this study aims to fabricate reversible pH‐responsive polymeric surfaces with controllable wettability using [poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate)‐block‐ poly(acrylic acid) (PHFBMA‐b‐PAA)] block copolymers. To attain this aim, three block copolymers with different PAA segment lengths were synthesized for the first time through Cu(0)‐mediated reversible‐deactivation radical polymerization and hydrolysis reaction. pH‐induced controllable wettability was achieved by spin‐coating the resulting block copolymers onto silicon wafers. Results showed that the pH‐responsive wetting behavior was introduced by incorporating the PAA block, and that the responsiveness of as‐fabricated surfaces was greatly influenced by PAA content. All three evolutions of water contact angle with pH shared a similar inflection point at pH 5.25. Furthermore, on the basis of the wetting properties and mechanism understanding, the application of copolymer coated meshes in layered water/oil separation was exploited. Given their superhydrophilicity and underwater superoleophobicity, PHFBMA₇₀‐b‐PAA₁₄₈ and PHFBMA₇₀‐b‐PAA₂₁₁ coated stainless steel meshes (SSMs) can efficiently separate water from different mixtures of organic solvent and water with high flux. However, considering long‐term use, the PHFBMA₇₀‐b‐PAA₁₄₈ coated SSM with good stability may be the best copolymer for water/oil separation. Therefore, a coordination of structure, composition, and functionality was necessary to enable practical applications of the functional materials. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1758–1771, 2016     

Capillarity and water repellency of fabrics

A method of determining the contact angle of wetting of fibres in the capillaries of fabrics is proposed. A theoretical calculation of the angles of wetting of cotton and blended fabric fibres with water was performed in the condition of formation of a uniform hydrocarbon film on the surface of the fibres. The real contact angles of wetting of water-repellent fabrics were determined; they differ from the angles of wetting of uniform hydrocarbon films by 10-12% due to the presence of hydrophilic molecules of the emulsifiers in the modifying film.     

Influence of low‐temperature plasma conditions on wicking properties of PA/PU knitted fabric

Plasma surface treatment has been extensively applied in the textile industry for the modification of polymer materials. In this study low‐temperature plasma (LTP) is used for surface treatment of polyamide/polyurethane (PA/PU) knitted fabric. The envisaged plasma effect is an increase in the surface energy of the treated textile, leading toward improved hydrophilic properties. The knitted fabric was treated by LTP using three non polymerizing gases: oxygen, air, and carbon dioxide. After plasma treatment, wettability of samples was tested through their wicking properties measuring capillary rise after water bath contact. The PA/PU knitted fabric samples treated with different plasma gases exhibited different hydrophilic performances. The influence of plasma variables (discharge power, time, pressure) was investigated. Although the chemical characteristics of elastan (PU) and nylon (PA) threads are different, the study has demonstrated that plasma treatment can in the same time alter the surface‐wetting behavior of both the components of the knitted fabric. It was also shown how these treatments can be regulated to produce the desired level of hydrophilicity dependently on the request application. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008