Sol–gel preparation of ultralow refractive index silica coatings with hydroxypropyl‐beta‐cyclodextrin as porogen

Ultralow refractive index films were prepared based on a base‐catalyzed sol–gel process using methyltriethoxysilane (MTES), tetraethylorthosilicate (TEOS) as co‐precursors, and hydroxypropyl‐beta‐cyclodextrin (HPCD) as porogen. After further modification by hexamethylisilazane (HMDS), the lowest refractive index of these silica coatings obtained from the hybrid sol was 1.05 and the static water contact angles of the coatings increased from 66.4° to 128.7°. The effect of weight ratio of HPCD to SiO₂ on the refractive index and on the formation of coating films were systematically studied. The data showed that the films prepared with HPCD as porogen got a pore diameter around 4 nm. Compared with those templates such as poloxamer (F127), HPCD not only perform well in decreasing the refractive index of films, but also eliminate light scattering caused by mesopore of the film, will have potential value in the field of surfactant‐templated methods. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44686.     

Superhydrophobic surfaces with silane‐treated diatomaceous earth/resin systems

Superhydrophobic coatings were prepared using fluorosilane‐treated diatomaceous earth (DE) with either polyurethane or epoxy binders. The surface wettability and morphology of the films were analyzed using contact angle measurements and scanning electron microscopy (SEM), respectively. The water contact angles were studied as a function of the fluorocarbon fraction on DE and the particle loadings of treated DE in the coating. The contact angles exceeded 150° for coatings with at least 0.02 fluorocarbon fraction (mass of fluorosilane/mass of particle) on the DE and with 0.2 particle loadings (mass of treated particles/mass of coating). The water contact angles of the surfaces were dependent on the nature of the binder below 0.2 particle loadings of the superhydrophobic DE particles, but were independent of the binder type after attaining superhydrophobicity. The results were consistent with the superhydrophobicity resulting from the migration of the superhydrophobic DE moving to and covering the surfaces completely. It was also shown that the treatment with fluorosilanes restricted the pores in DE and reduces the specific surface area of the material. However, these changes had effectively no effect on the superhydrophobicity of the coatings. The results of this work clearly identify some important considerations relative to producing superhydrophobic coatings from inexpensive diatomaceous earth. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44072.     

Fabrication of superhydrophobic coatings based on nanoparticles and fluoropolyurethane

Hydrophobic nanosilica or nanofluoric particles were mixed with fluoropolyurethane resin to fabricate superhydrophobic coatings that have contact angles higher than 145°. These coatings were prepared from the simple mixing of nanoparticles in fluoropolymer and were cured at room temperature. Different fractions of nanosilica, nanofluoric particles, and the combination of them were used to find the best formulations of superhydrophobic coatings. Contact angle, contact angle hysteresis, sliding angle, hardness, and UV durability tests were conducted to find the effectiveness of these coatings. The results showed that only fluoropolyurethane coatings containing nanosilica or the combination of it and fluoric particles were superhydrophobic. Also, the hardness of coatings was increased by raising nanoparticle concentrations. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Properties of organic–inorganic composite materials prepared from acrylic resin emulsions and colloidal silicas

To design an organic–inorganic composite material with colloidal silica as the inorganic component, an acrylic resin emulsion and an organic silane hybridized acrylic resin emulsion were prepared by emulsion polymerization. The organic–inorganic composite films were prepared by blending the emulsion and the colloidal silica. The contact angles for water, gloss at 60°, and the transparencies of those films were measured. The dispersion state of colloidal silica in films was observed with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). From these results, the contact angle for water of the organic–inorganic composite film obtained from the silane hybridized acrylic resin emulsion was lower than that of the organic–inorganic composite film obtained from an acrylic resin emulsion. The contact angles for water in organic–inorganic composite films with colloidal silicas were lower than those of the films without the colloidal silicas. The films prepared from silane hybridized acrylic resin emulsion composites with colloidal silicas of less than 100 nm were more hydrophilic. SEM and TEM observations demonstrated that some aggregations of the small colloidal particle silica were densely dispersed on the film surface. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2051–2056, 2006     

Porous water repellent silica coatings on glass by sol–gel method

Development of the solid surfaces with water-repellent and self-cleaning ability has attracted much research interest in recent years. In the present research work, we have prepared water repellent silica coatings on glass at room temperature (~27 °C) by sol gel process and surface silylation technique. Coating sol was prepared by keeping the molar ratio of tetramethoxysilane (TMOS), methanol (MeOH) and water (H₂O) constant at 1:12.36:4.25, respectively, with 0.01 M NH₄F. The dip coated silica films were surface silylated using two different silylating agents namely hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDZ). The HMDSO and HMDZ in hexane solvent were varied from 0 to 1 vol.% and silylation period was varied from 1 to 3 h. The HMDSO and HMDZ modified films showed dense and porous surface morphology, respectively. The HMDSO modified silica films showed static water contact angle of 122° whereas HMDZ modified films showed 165°. The HMDZ modified films displayed the extreme water repellency comparing with that of lotus leaves. The silica films were characterized by surface profilometer, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared microscopy, thermal and chemical aging tests, optical transmission and static water contact angle measurements.     

Polymer derived SiC environmental barrier coatings with superwetting properties

Surfaces with superwetting capabilities can be used for corrosion protection, self-cleaning and bio-fouling protection amongst other applications. In this work, we present a method to produce a SiC coating with an almost superhydrophobic behavior exhibiting water contact angles of 145±3°. Ceramic coatings were produced by the pyrolysis of polycarbosilane as a preceramic precursor of SiC. Aluminum and carbon powders were used as active and passive fillers to compensate for the volume shrinkage of polycarbosilane during pyrolysis. The effects of particle size (Al particles ranging from 0.8 to 10 µm) and concentration 10–30% wt.) C and Al of both fillers were studied to produce defect-free ceramic coatings. We have observed that the fillers used not only affected the microstructure but also the surface roughness. We show that the addition of carbon fillers can increase the water contact angle of the ceramic from 42° up to 141°. The combination of carbon and aluminum fillers resulted in water contact angles up to 145°.     

Effect of oxygen plasma treatment on non-thrombogenicity of diamond-like carbon films

The non-thrombogenicity of oxygen-plasma-treated DLC films was investigated as surface coatings for medical devices. DLC films were deposited on polycarbonate substrates by a radio frequency plasma enhanced chemical vapor deposition method using acetylene gas. The deposited DLC films were then treated with plasma of oxygen gas at powers of 15 W, 50 W, and 200 W. Wettability was evaluated by water contact angle measurements and the changes in surface chemistry and roughness were examined by X-ray photoelectron spectroscopy and atomic force microscope analysis, respectively. Each oxygen-plasma-treated DLC film exhibited a hydrophilic nature with water contact angles of 11.1°, 17.7° and 36.8°. The non-thrombogenicity of the samples was evaluated through the incubation with platelet-rich plasma isolated from human whole blood. Non-thrombogenic properties dramatically improved for both 15 W- and 50 W-oxygen-plasma-treated DLC films. These results demonstrate that the oxygen plasma treatment at lower powers promotes the non-thrombogenicity of DLC films with highly hydrophilic surfaces.     

A simple method for the fabrication of silica-based superhydrophobic surfaces

The present article reports on a simple and convenient method for the fabrication of superhydrophobic surfaces based on silica particles by spraying the as-prepared silica suspension containing silica sol and silica microspheres on the substrate. The morphologies of the silica particulate coatings could be controlled by varying the silica microsphere concentration. The silica particulate coatings as prepared were exceptionally rough and superhydrophilic, with water contact angles less than 5°. The surface silanol groups of the hydrophilic coatings could be functionalized using 1H,1H,2H,2H-perfluorodecyltriethoxysilane to form hydrophobic groups. The resulting surface showed excellent superhydrophobic property with water contact angle up to 165.6 ± 0.9° and sliding angle of 3.5 ± 0.4°. In addition, the superhydrophobicity of the coating possessed a good stability after 3 months of exposure in air for a wide range of pH values.     

Optimization of amphiphobic structural surface thickness in relation to its functionality on stainless steel plates

Fluorine‐based amphiphobic coatings have been widely used in commercial textiles to provide water‐ and oil‐repelling abilities. However, few reports from the literature survey have discussed the surface structural effects of the coated substrate on amphiphobicity. In this research, various thickness amphiphobic coatings based on mixed epoxy, tetraethylorthosilicate, and a particular alkoxysilane with fluorinated side chains (F‐silane) were deposited on Grade 420 stainless steel plates. Film amphiphobicity is characterized by measuring the water and oil contact angles of the coating. Film morphology is examined using atomic force microscopy. The deposited films free of F‐silane are thinner than 150 nm. The films become thick at high F‐silane volume percentage with the surface cavities, ridges, and granules being masked out. On the addition of F‐silane, the water contact angle of the deposited films increases up to 105° and then reaches a plateau of ～ 107° with increasing F‐silane. In contrast, the oil contact angle increases up to 60° at first and then slowly declines with the F‐silane concentration. The total drop of oil contact angle by ～ 20° was attributed to the masking out of surface features on film thickening. This indicates that the surface oleophobicity depends on surface structures. Therefore, improving surface amphiphobicity correlates with creating more refined multiscale surface structures during the industrial manufacturing process of steel plate, prior to surface modification by F‐silane. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41003.     

Ultrahydrophobic silica films by sol–gel process

Wettability of solid surfaces is a crucial concern in our daily life as well as in engineering and science. The present research work describes the room temperature (27 °C) synthesis of adherent and water repellent silica films on glass substrates using vinyltrimethoxysilane (VTMS) as a hydrophobic reagent by a single step sol–gel process. The silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), water (H₂O) constant at 1:14.69:5, respectively, with 0.01 M NH₄F throughout the experiments and the VTMS/TEOS molar ratio (M) was varied from 0 to 0.97. The effects of M on the surface structure and hydrophobicity have been researched. The static water contact angle as high as 144° and water sliding angle as low as 14° was obtained for silica film prepared from M = 0.97. The hydrophobic silica films retained their hydrophobicity up to a temperature of 255 °C and above this temperature the films became superhydrophilic. The prepared silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity test and static and dynamic water contact angle measurements.     

Preparation and water resistance of crosslinked waterborne polyurethaneurea

Abstract

Two series of cross-linked polyurethaneurea (PUU) aqueous dispersions with polyoxypropylene glycerol and pentaerythritol as internal cross-linking agents were prepared and characterised. The results revealed that in comparison with the uncross-linked one, the cross-linked PUU films exhibited excellent waterproof performance and mechanical properties. The amount of water absorption was as low as 2?5 wt-%, the contact angle of water on the surface of this kind of film was as high as 96°, and the tensile strength was as high as 42?8 MPa. The cross-linked PUU films with polyoxypropylene glycerol and pentaerythritol as cross-linked agents showed different properties at the same cross-linking agent content. The prepared triol-cross-linked or tetra-cross-linked PUUs had great potential application in meeting the highly diversified demands in modern technologies such as coatings, leather finishing, adhesives, sealants, plastic coatings and wood finishes, where high water resistance and durability were required.     

Preparation of super‐hydrophobic film with fluorinated‐copolymer

Organic superhydrophobic films were prepared by utilizing TA‐N fluoroalkylate (TAN) and methyl methacrylate (MMA) copolymer as water‐repellent materials and inorganic silica powder as surface roughness material has been developed. Coating solutions prepared by adding silica powders into copolymer solution directly (one‐step method) and by adding silica powders into monomers and allowing them to react (two‐step method). The results showed that contact angles of the films prepared by one‐step method (37.6 wt % of silica powders in the coating solution) were greater than 150°, but the transmittance of the film at visible light was only 30%. On the other hand, the contact angle of films prepared by two‐step method (20 wt % of silica powders in the coating solution) was greater than 160° and the transmittance of the film was greater than 90%. The contact angle of the film prepared by poly(octyl acrylate), POA, was 32.1°, but while introducing silica powder into the system, the contact angle of the film was reduced to be smaller than 5°. Thus, superhydrophobic and superhydrophilic films can be obtained by introducing a roughening material on the hydrophobic surface and the hydrophilic surface, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1646–1653, 2007     

Coatings to prevent frost

The ability of hydrophobic, organic–inorganic hybrid coatings to decelerate frost propagation was investigated. Compared to a bare aluminum surface, the coatings do not significantly reduce the freezing probability of supercooled water drops. On both surfaces, the probability for ice nucleation at temperatures just below 0°C, for example at ?4°C, is low. Freezing of a single drop on aluminum leads, however, to instant freezing of the complete surface. On hydrophobic coatings, such a freezing drop is isolated; the frozen area grows slowly. At ?4°C surface temperature in a +12°C/90% relative humidity environment, on surfaces providing a water contact angle hysteresis of about 10° and receding water contact angles higher than 90°, a rate for the growth of the average radius of the frozen area of about 2 µm/s was observed. Submitting the surface to an airflow of 1 m/s led to faster frost spreading in flow direction. Although the airflow compromised the anti-ice properties to some extent, the application of the hydrophobic coating in a heat recovery ventilation experiment extended the time interval between defrosting cycles by a factor of 2.3.     

Preparation and characteristics of a waterborne preventive stain coating material with organic-inorganic composites

With the goal of developing a waterborne coating material that prevents staining, organic-inorganic composites prepared from colloidal silica and two types of acrylic resin emulsions were investigated as exterior coatings. conventional acrylic resin emulsion and organic silane hybridized acrylic resin emulsion prepared by emulsion polymerization were mixed with colloidal silica to form organic-inorganic comiposite films. The addition of colloidal silica to emulsions yielded films with higher hydrophilicities, as indicated by lower water contact angles for these films in comparison to films without colloidal silica. The water contact angles of organic silane hybridized acrylic resin emulsion/colloidal silica films were lower than those of acrylic resin emulsion/colloidal silica films. Composite films containing colloidal silica particles smaller than 100 nm in diameter showed high hydrophilicities. Observations of the dispersed state of colloidal silicaparticles in organic-inorganic composite films by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that colloidal silica particles were densely aggregated on the film surface. Outdoor exposure tests of the coating materials prepared from organic silane hybridized acrylic resin and colloidal silica particles with diameters of 7.5 nm showed excellent stain resistance.     

Thermal and electrical behavior of polyimide/silica hybrid thin films

Silica‐containing polyimide films were prepared by sol‐gel technique using a poly(amic acid) and tetraethoxysilane. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(3‐aminophenoxy)benzene and an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. The properties of these films, such as water vapors sorption capacity, dynamic contact angles and contact angle hysteresis, thermal, and electrical behavior have been evaluated with respect to their structure. The polymer films exhibited good thermal stability having the initial decomposition temperature above 450°C, glass transition temperature in the range of 223?228°C, and low‐dielectric constant in the range of 2.64?3.16. Two subglass transitions, γ and β, were evidenced by dynamic mechanical analysis and dielectric spectroscopy. The surface morphology and the roughness were investigated by atomic force microscopy and scanning electron microscopy. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Long-term-durable anti-icing superhydrophobic composite coatings

We prepared carbon-based superhydrophobic composite coatings through a quick technique, merging multiwalled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) to obtain hierarchical nanostructures on fiber-reinforced polymer (FRP) sheets; this was followed by supercritical fluid (SCF) processing and physical mixing (PM). The prepared SCF–MWCNT–CNF and PM–MWCNT–CNF composite coatings showed high water contact angles of 171.6 and 160°. The surface morphologies of the composite coatings revealed a lot of even nanostructures and folding at high magnifications. A high number of CNFs were added to the MWCNTs to initiate different nanoroughnesses in the composite coatings. The as-prepared superhydrophobic composite coatings showed excellent anti-icing properties, as indicated by the supercooled water droplet (-20°C) test under environmental conditions. Also, the surface of the SCF–MWCNT–CNF superhydrophobic composite coating showed excellent antifouling properties. We studied the surface wettability increasing different temperatures (30–180°C) in the SCF–MWCNT–CNF composite; this exposed the fact that the FRP sheets were thermally stable up to 100°C, and a while later, they changed from a superhydrophobic state to a superhydrophilic state at 180°C. This study revealed an economically workable method for the preparation of MWCNT–CNF composites with SCF techniques. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47059.     

水在不同接触角微柱群内的流动特征

采用向改性有机硅稀溶液中加入2%全氟辛基氟硅烷以及微纳米粒子的方法制备疏水液,通过改变微纳米粒子添加量调控疏水液固化成涂层后的表观接触角,紫铜叉排排列微柱群表面经不同疏水液处理后接触角分别为99.5°、119.5°和151.5°(水为工质),并测试流道内流动阻力和压力降。实验结果表明,相同Reynolds数(Re)下流道内摩擦因子(f)比疏水处理前有明显下降,主要是由于疏水性界面的张力作用所致;相同Re下,接触角越大,疏水涂层双重结构中微纳米凸起间距越小,去离子水与空气接触面增大,使得摩擦因子减小;随Re增加,3种涂层实验段内的减阻率均不断降低。     

Wettability alteration of gas condensate reservoir rocks to gas wetness by sol–gel process using fluoroalkylsilane

Natural gas is becoming a very important energy source in recent years. A sharp reduction has been observed in gas deliverability in many low permeability gas reservoirs due to bottom‐hole pressure drops below the dew point pressure. It is an established fact that altering the wettability of reservoir rocks from liquid wetness to gas wetness could improve the gas deliverability. In this study, a new polymeric surfactant coating for altering the wettability of Sarkhun reservoir rocks was prepared by using a sol–gel process. Perfluorodecylsilane (PFDS) and triethoxysilane (TEOS) were used to obtain an inorganic‐organic network via hydrolysis and polycondensation reactions. The effect of this method was examined by various characterization tests such as FTIR, SEM, and EDX, static contact angle and imbibition tests for wettability alteration. The experimental results revealed that, the prepared polymeric network including the terminal fluorine groups were effective and provided sufficient repelling characteristics towards oil and water. Static contact angles were raised from 30 to 130° for water, and from <5 to 60° for condensate after sol–gel treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Superoleophobic and conductive carbon nanofiber/fluoropolymer composite films

A solution-based, large-area coating procedure is developed to produce conductive polymer composite films consisting of hollow-core carbon nanofibers (CNFs) and a fluoroacrylic co-polymer available as a water-based dispersion. CNFs (100 nm dia., length ～130 μm) were dispersed by sonication in a formic acid/acetone co-solvent system, which enabled colloidal stability and direct blending of the CNFs and aqueous fluoroacrylic dispersions in the absence of surfactants. The dispersions were sprayed on smooth and microtextured surfaces, thus forming conformal coatings after drying. Nanostructured composite films of different degrees of oil and water repellency were fabricated by varying the concentration of CNFs. The effect of substrate texture and CNF content on oil/water repellency was studied. Water and oil static contact angles (CAs) ranged from 98° to 164° and from 61° to 164°, respectively. Some coatings with the highest water/oil CAs displayed self-cleaning behavior (droplet roll-off angles <10°). Inherent conductivity of the composite films ranged from 63 to 940 S/m at CNF concentrations from 10 to 60 wt.%, respectively. Replacement of the long CNFs with shorter solid-core carbon nanowhiskers (150 nm dia., length 6–8 μm) produced stable fluoropolymer–nanowhisker dispersions, which were ink-jetted to generate hydrophobic, conductive, printed line patterns with a feature size ～100 μm.     

Zwitter-wettable acrylic polymeric coating on glasses for anti-fog applications

Anti-fog coatings have received significant attention because of their versatile applications to reduce light scattering during high humid conditions. Primarily, hydrophilic/superhydrophilic coatings are applied upon the transparent substrate to improve visibility at high humidity. The high solubility of the hydrophilic/superhydrophilic coatings in water is the main drawback for their long-term operational durability. We will report for the first time the development of functional copolymers which produces water insoluble hydrophilic coating upon application on glass surfaces. Such surfaces are commonly known as “Zwitter-Wettable” surfaces that have been developed from entirely polymeric substances using methacrylic and acrylic monomers. A series of random copolymers were synthesized using free radical polymerization of the common and commercially available monomers which were subsequently characterized using various analytical techniques, such as, GPC, ¹H-NMR, and FTIR. These newly designed copolymers contained both the hydrophobic parts made up of methyl and 2-ethylhexyl groups, which provide good stability under high humid conditions and hydroxyl and carboxylic acid groups which will provide the required hydrophilicity or water absorption capacity. These polymeric coatings on the glass surfaces exhibit water advancing contact angles in the range of 57 ± 3° to 78 ± 3° with excellent anti-fog property. The anti-fog property of the polymeric films could be tuned easily by changing the ratio of hydrophobic and hydrophilic monomers.