Novel surfactant-free waterborne acrylic-silicone modified alkyd hybrid resin coatings containing nano-silica for the corrosion protection of carbon steel

We report a novel waterborne acrylic-silicone modified alkyd nanocomposite latex containing nano-silica prepared by the surfactant-free miniemulsion polymerization. The influences of γ-methacryloxy-propyltrimethoxysilane- (MPS-) modified nano-silica particle contents to the thermal, mechanical and anti-corrosion performance of hybrid latex coatings were studied. The results revealed that the incorporation of nano-silica particles into latex films could directly increase the thermal stability and mechanical properties. Electrochemical corrosion studies revealed that these nanocomposite coatings exhibited superior corrosion resistance performance (inhibition efficiency 99.36% and corrosion rate 1.09 × 10 ^?3 mm per year) than that of the control system (without SiO₂ NPs).     

Heat‐resistant hydrophobic–oleophobic coatings

Thermally and chemically durable hydrophobic oleophobic coatings, containing different ceramic particles such as SiO₂, SiC, Al₂O₃, which can be alternative instead of Teflon, have been developed and applied on the aluminum substrates by spin‐coating method. Polyimides, which are high‐thermal resistant heteroaromatic polymers, were synthesized, and fluor oligomers were added to these polymers to obtain hydrophobic–oleophobic properties. After coating, Al surface was subjected to Taber‐abrasion, adhesion, corrosion, and thermal tests. The effects of the particle size of ceramic powders, organic matrix, and heat on the coating material were investigated. Coating material was characterized by FTIR spectrophotometer. Surface properties and thermal resistance of the coating materials were investigated by SEM and TGA analyses. After thermal curing, contact angles of these coatings with H₂O and n‐hexadecane were measured. It was observed that coatings like ceramic particles are more resistant against scratch and abrasion than the other coatings. Also, they are harder than coatings, which do not include ceramic particles. It was seen that coatings, containing Fluorolink D10H, have high‐contact angles with water and n‐hexadecane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2386–2392, 2006     

Preparation, characterization and properties of UV-curable waterborne polyurethane acrylate/SiO2 coating

The UV-curable waterborne polyurethane acrylate (UV-WPUA) oligomer was first prepared based on isophorone diisocyanate (IPDI), polyether polyol (NJ-220), dimethylol propionic acid (DMPA), and hydroxyethyl methyl acrylate (HEMA) via an in situ method. With the different content tetraethoxysilane (TEOS) and 3-glycidyloxypropyltrimethoxysilane (GLYMO) as coupling agents, a series of waterborne UV-WPUA/SiO₂ oligomers were prepared by the sol?Cgel process. The physical and mechanical properties of the UV-WPUA and UV-WPUA/SiO₂ hybrid coating materials were measured. The UV-WPUA and WPUA/SiO₂ hybrid materials were characterized using FTIR spectra, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD) measuring apparatuses to determine their structures, thermal properties, surface morphologies, etc. The results showed the SiO₂ particles of the hybrid materials had wide dispersion, forming a good interfacial bonding layer on surfaces. The tensile strength, water resistance, and thermal properties of the hybrid materials were better than those of the UV-WPUA. The resulting UV-WPUA/SiO₂ hybrids are promising for a number of applications, e.g., for high-performance water-based UV-curable coatings.     

Synthesis and Characterization of Anti-fungus,Anti-corrosion and Self-cleaning Hybrid Nanocomposite Coatings Based on Sol–Gel Process

Anti-corrosion, anti-fungus, and self-cleaning properties of coatings containing ZnO–TiO₂, SiO₂–TiO₂ and SiO₂/TiO₂/ZnO nanoparticles synthesized based on sol–gel precursors using tetra methoxysilane, 3-glycidoxypropyl trimethoxysilane, tetra (n-butyl orthotitanate) and zinc acetate dihydrate were investigated by FESEM, EDAX and TEM analyses. Results indicated uniform dispersion of inorganic nanoparticles in the range of 20–40 nm in size. Anti-corrosion property of the hybrid coating was characterized by EIS measurements and parametrically analyzed in an equivalent circuit when the coating was exposed to salt solution. Results showed that, ZnO and TiO₂ nanoparticles enhance anti-corrosion property of the hybrid coatings. Anti-fungus and anti-bacterial properties of the coatings were determined by diameter of inhibition zone and inhabitation of bacterial growth, respectively. The coating containing ZnO and TiO₂ nanoparticles showed anti-fungus and anti-bacterial properties which were related to their photocatalytic properties. Degradation of methylene blue in aqueous solution was determined by UV–Visible tests which indicated self-cleaning property of the coatings containing ZnO and TiO₂ nanoparticles.     

Preparation,characterization of nano-silica/fluoroacrylate material and the application in stone surface conservation

A series of fluoroacrylate (FPA) and nano-silica/fluoroacrylate were prepared. The properties including physical properties, mechanical behavior and contact angle of FPA were investigated. According to the results, the optimal fluoride content can be screened. The nano-silica/fluoroacrylate (SiO₂/FPA) materials were characterized by fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) and transmission electron microscope (TEM). The surface morphology and mineralogical analysis of the stone samples were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The prepared coating was selected to protect on the stone surface. Aimed at evaluating the coating performance, the protective performances were also evaluated by artificial aging test. The results indicated that when the content of hexafluoro-butyl methacrylate (HFMA) was 8.0 wt% and the content of SiO₂ was 4.0 wt%, the prepared material has good compatibility and appearance with stone relics. The protective coating material for protection of chosen Jiaoshan Steles Grove (China) is noticeable and it can be widely applied to the protection of stone relics.     

Effect of ceria and zirconia nanoparticles on corrosion protection and viscoelastic behavior of hybrid coatings

Organic–inorganic hybrid nanocomposite coatings contain inorganic particles that are dispersed in organic phase in nanometric dimensions. Ceria and zirconia colloidal dispersions are uniformly distributed in the epoxy silica-based hybrid nanocomposite by sol–gel method and coated on 1050 aluminum alloy substrate with spin-coating technique. The hybrid sol is prepared by organic–inorganic precursors formed by hydrolysis and condensation of 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate (TEOS) in acidic solution using bisphenol A as networking agent and 1-methylimidazole as initiator in the presence of various ratios of ZrO₂ and CeO₂ colloidal nanoparticles. Particle size distribution, surface morphology and inorganic components distribution were determined by scanning electron microscopy (SEM) and EDXA techniques. SEM and Si, Zr, Ce mapping micrographs proved the uniform distribution of nanoparticles in the coatings. Transmission electron microscopy indicated that the nanoparticles dimension stay at the nanoscale level. The glass transition temperature (T _g) and loss properties (damping) of coatings were evaluated by dynamic mechanical thermal analysis. The corrosion protection of the coatings on the 1050 AA substrate was studied by potentiodynamic measurements. The results indicated that by introducing ceria nanoparticles in 1:1 molar ratio to TEOS in coating composition, corrosion protection was improved. However, the simultaneous presence of two nanoparticles (i.e., ceria and zirconia in 1:1 molar ratio) in the coating compositions increased the corrosion protection efficiency up to 99.8 %. The multiple glass transitions and shifting to higher and wide range of temperatures by adding ceria and zirconia nanoparticles indicated a better network interaction between inorganic nanoparticles and organic molecular chains which also led to better corrosion protection of the coating in this composition.     

超临界CO2快速膨胀法制备SiO2/聚氨酯超疏水涂层

用超临界CO₂快速膨胀法制备了SiO₂/聚氨酯超疏水涂层。首先用十三氟辛基三乙氧基硅烷（F-硅烷）和γ-(甲基丙烯酰氧基)丙基三甲氧基硅烷（KH-570）改性纳米二氧化硅,制备出含双键的纳米二氧化硅粒子,将其分散在超临界CO₂中,再利用超临界CO₂快速膨胀法将其喷射到双键封端的且已添加了引发剂的聚氨酯涂层表面,通过加热,使纳米二氧化硅粒子接枝在聚氨酯涂层表面,形成稳固粗糙结构,获得了超疏水性质。研究了喷嘴温度、反应釜温度和压力、偶联剂配比、表面粗糙度对涂层疏水性的影响。结果表明：涂层的静态水接触角可达到169.1°±0.6°;在喷嘴和釜内温度都为90℃,釜内压力为16 MPa,F-硅烷和KH-570配比为1∶1,表面粗糙度为7.3 μm时,所制得涂层具有较好的超疏水性,且具有优良的耐刮伤性。该法高效环保,涂层性能优良,适于大面积制备。     

Sol–gel preparation and characterization of antibacterial and self-cleaning hybrid nanocomposite coatings

ZnO–TiO₂, SiO₂–TiO₂, and SiO₂–TiO₂–ZnO hybrid nanocomposite coatings were synthesized based on sol–gel precursors including tetramethoxysilane (TMOS), 3-glycidoxypropyl trimethoxysilane (GPTMS), tetra(n-butyl orthotitanate) (TBT), and zinc acetate dihydrate. The hybrid network was characterized by FTIR, FESEM, and EDAX techniques. Results indicated that inorganic particles’ size was of nanoorder (20–30 nm), with very uniform distribution and dispersion. Photocatalytic and self-cleaning activities of these coatings were further investigated by degradation of methylene blue in an aqueous solution (20 ppm) at visible light irradiation, indicating photocatalytic performance of the coatings containing ZnO and TiO₂ nanoparticles. The antibacterial effect of the coatings was investigated for inhibition and inactivation of cell growth, with the results showing the same antibacterial activity for ZnO–TiO₂ and SiO₂–TiO₂–ZnO coatings against Escherichia coli and Staphylococcus aureus; the activity was, however, higher than that of SiO₂–TiO₂ hybrid nanocomposite coatings.     

Wear,thermal, and physical properties of fluorine-containing polyimide/silica hybrid nanocomposite coatings

This study prepared fluorine and SiO₂ particles containing organic–inorganic hybrid polyimide nanocomposite coatings (PISFs) with inorganic content in the range of 5–20% in pure polyimide solutions via the sol–gel process. Polyimide hybrid structures containing fluorine and SiO₂ particles were synthesized by using perfluorooctyltriethoxysilane and tetraethyl orthosilicate. These formulations were applied on aluminum sheets by using a 75 μm wire wound applicator, and the coatings were cured for 8 h at room temperature and then 24 h at 100 °C. Increased inorganic contents caused slight decreases in the initial decomposition temperatures, but the char yield values increased for PISF15 and PISF20. All samples exhibited hydrophobic properties. When all samples were compared, PISF5 and PISF10 exhibited hydrophobicity, high wear resistance and thermal properties. Additionally, PISF5 and PISF10 showed high adhesion, hardness, and methyl ethyl ketone solvent resistance. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47399.     

Fabrication of superhydrophilic self-cleaning SiO2–TiO2 coating and its photocatalytic performance

Generally, superhydrophilic self-cleaning coatings are prepared from semiconductors with photocatalytic properties. Organic pollutants attached to the coating surface can be degraded by its photocatalytic performance realizing a self-cleaning goal. Herein, SiO₂–TiO₂ composite particles were fabricated by the hydrolysis and precipitation of TiOSO₄, and SiO₂ microspheres were chosen as carriers, which are inexpensive and environmentally friendly. Then, superhydrophilic self-cleaning SiO₂–TiO₂ coatings were fabricated by spraying the composites on the surfaces of substrates. The morphology, structure and self-cleaning performance of the SiO₂–TiO₂ coating were characterized and tested. The results revealed that nano-TiO₂ was loaded on the surfaces of SiO₂ microspheres uniformly forming a hierarchical micro/nanostructure. The SiO₂–TiO₂ composite particles exhibited excellent photocatalytic degradation performance, and the degradation rate of methyl orange (10 ppm) was more than 98% under UV irradiation for 40 min. Furthermore, the coating prepared with the SiO₂–TiO₂ composite particles exhibited superhydrophilicity. A water droplet spreads completely on the coating surface in 0.35 s, and the contact angle reaches 0°. In addition, rhodamine B (RhB) and methylene blue (MB) on the coating surface can be degraded efficiently under sunlight irradiation. The SiO₂–TiO₂ composite particles can be sprayed directly on the surfaces of concrete, brick, wood, and glass slides. Therefore, the particles showed good adaptability to different substrates. The superhydrophilic property was due to the hydrophilicity of SiO₂ and TiO₂, the hierarchical micro/nanostructure of the SiO₂–TiO₂ composites, and the photoinduced superhydrophilicity of TiO₂. The above experimental results show that the as-prepared superhydrophilic self-cleaning SiO₂–TiO₂ coating has a large application potential.     

Nanosize Polyacrylamide/SiO2 Composites by Inverse Microemulsion Polymerization

Nanosize polyacrylamide/silica (PAM/SiO₂) composites were prepared by water- in-oil (W/O) microemulsion process. In this system, aqueous solution of acrylamide containing disperse 10 nm size silicon dioxide was used as the dispersed phase of the microemulsion while the dispersion medium was sodium bis (2-ethylhexyl) sulfosuccinate (AOT)/toluene solution. The size of the synthesized PAM/SiO₂ nanocomposites was 38–76 nm as determined by dynamic light scattering (DLS). The incorporation of nanosize silica filler reduces the particle size of PAM latex. It had also been found that the size of composite particles decreases with increasing filler loading along with better polydispersity. The presence of silica particles in the polymer latex particles and interaction of polymer chains with silica particles in hybrid nanocomposites were characterized by Fourier transform infra red spectrophotometry (FTIR), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The TGA results showed improved thermoresistance and high thermal stability behavior of hybrid composites. The DSC measurements revealed that the incorporation of filler favors crystallization, increases the enthalpy of melting and thermal stabilization of the synthesized composite particles. A scanning electron microscope (SEM) was used to study the morphology and topography of the prepared nanocomposites.     

Synthesis and characterization of PMMA/SiO2 organic–inorganic hybrid materials via RAFT‐mediated miniemulsion polymerization

In this article, we first carried out the surface modification of SiO₂ using silane coupling agent KH570, and then prepared PMMA/SiO₂ organic–inorganic hybrid materials by conventional free radical polymerization and RAFT polymerization in miniemulsion, respectively. The kinetics comparisons of these two polymerizations were studied. PMMA/SiO₂ hybrid materials were characterized by gel permeation chromatography, differential scanning calorimetry and thermogravimetric analysis. Experimental results indicated that the polymerization behavior of MMA in miniemulsion showed controlled/living radical polymerization characteristics under the control of RAFT agent. Incorporation of RAFT agent and SiO₂ nanoparticles improved the thermal properties of polymers, the thermal stability of polymers increased with increasing content of SiO₂ nanoparticles. The structures and morphologies of SiO₂, modified SiO₂, and PMMA/SiO₂ hybrid materials were characterized by FT‐IR and TEM. TEM results showed that the addition of modified SiO₂ nanoparticles to miniemulsion polymerization system obtained different morphology latex particles. Most of modified SiO₂ nanoparticles were wrapped by polymer matrix after polymerization. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Effects of nanosilica and titanium oxide on the performance of epoxy–amine nanocoatings

Different types of composite coatings were prepared by the blending of colloidal nanosilica (SiO₂) and titanium dioxide (TiO₂) in epoxy resin to investigate their coating performances. A fixed amount of silica nanoparticles (20 wt %) and different amounts (5, 10, and 15 wt %) of microsized TiO₂ particles were used in the coatings. The functional groups of the formulated coatings were confirmed by Fourier transform infrared spectroscopy. These results indicate that the SiO₂–TiO₂ particles interacted well with epoxy. Scanning electron microscopy images of the composite coatings revealed a good dispersion of TiO₂ particles at a lower amount of loading; this improved the adhesiveness, glass-transition temperature, thermal stability, and chemical resistance properties. At higher loadings, the performances decreased. The composite coatings were also characterized by their UV radiation-absorption properties with an ultraviolet–visible spectrophotometer. Interestingly, this property was found to be enhanced at higher loadings. An impressive result was noticed in the nanocomposites in terms of oxygen transmission rate performance compared to that of the neat epoxy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47901.     

TEM,XPS and thermo-mechanical properties of novel sustainable hybrid coatings

This work contributes to the development of a new generation of protective coatings composed of organic–inorganic materials. A silica based hybrid film was used in this work as high performance materials. The silica sol–gel film reveals enhanced thermo-mechanical properties in comparison with the pure polymer film. Herein, we demonstrate the possibility of employing cheap SiO₂ as prospective nano-fillers for hybrid coatings with active thermo-mechanical properties. Organic–inorganic hybrid coatings based on polyimide and silica were synthesized through a simple physical mixing technique. 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA), benzene-1,3-diamine (BDA), 3,3′-oxydianiline (ODA) and SiO₂, were used as precursors for the hybrid coatings. These hybrid coatings were deposited via spin coating onto a galvanized iron, aluminum and copper in order to study the adhesive strength. The effects induced by the silica content on the mechanical properties of the coated samples were investigated. The mechanical properties of hybrid composite were found to be enhanced compared to polyimide coating. The main objective was to observe potential improvements in the mechanical and thermal properties of PI–silica hybrid films. Morphology, and structural changes in the composite films were studied as well as adhesion and impact strength and these characteristics were compared with those of unreinforced polyimide films.     

Assessment of the performance of Y2SiO5-YSZ/YSZ double-layered thermal barrier coatings

Y₂SiO₅ is a promising material for the thermal barrier coatings due to its low thermal conductivity, high temperature stability and exceptional resistance for molten silicate attack. However, it suffers low fracture toughness and low coefficient of thermal expansion compared with yttria-stabilized zirconia (YSZ). In this study, a composite coating approach, i.e., incorporating YSZ into Y₂SiO₅ coating, was employed to overcome those limitations. The double-layered Y₂SiO₅-YSZ/YSZ coatings were fabricated using atomospheric plasma spraying and tested under thermal cycling at 1150 °C. The phase compositions, microstructure, mechanical properties and the failure behavior were evaluated. It was found that the amorphous phase during spraying would crystallize at high temperature accompanied by volume shrinkage, leading to cracks and spallation in the coating. With YSZ addition, the composite coatings exhibited a much longer lifetime than the single phase Y₂SiO₅ coating due to a lower volume shrinkage and enhanced toughness.     

Superior Performance of Ablative Glass Coatings Containing Graphene Nanosheets

Glass compositions in the Y₂O₃–Al₂O₃–SiO₂ (YAS) system are envisaged as promising coatings for high‐temperature protection, in particular for the thermal protection systems (TPS) looked for aerospace applications. Recently, thermally sprayed YAS hybrid coatings containing a small amount of graphene nanoplateletes (GNPs) showed enhanced performance as compared to the blank YAS coating, demonstrated by the occurrence of unusual electrical conductivity for these glasses and the development of better mechanical compliance, both phenomena associated with the presence of GNPs. Nevertheless, a crucial issue is to demonstrate if these kinds of coatings would also have superior behavior under ablation conditions, particularly regarding the mentioned TPS applications. This work goes far beyond, exploring the ablative behavior of new YAS/GNPs coatings flame sprayed over SiC substrates. These essential tests were carried out under laboratory conditions, reaching limit temperatures of 1350°C while blowing gas. Results evidence that hybrid coatings having just 1.05 vol% GNPs show enhanced ablation resistance, actually withstanding up to 30 thermal cycles (between 200°C and 1350°C) without apparent damage. This satisfactory performance is linked to the benefits of the GNP additions, and fundamentally to the higher emissivity and the directional thermal conduction characteristics of the hybrid coatings—produced by the formation of a GNP network with a preferential surface parallel arrangement—that preclude the creation of hot spots and also hinder heat propagation toward the substrate; accordingly, coating degradation is constrained to the uppermost layer of these coatings.     

Angular absorptance and thermal degradation analysis of TiB2/Ti(B,N)/SiON/SiO2 multilayer solar absorber coating

Multilayer solar selective absorber coatings have been developed in the last few decades. The thermal stability in terms of microstructure gives an insightful understanding of the optical properties of such coatings. In this context, we extensively utilized transmission electron microscopy (TEM) analysis to establish the thermal stability of TiB₂/Ti(B,N)/SiON/SiO₂ coating, under thermal cycling/continuous heating to 500°C in vacuum for 250 h. In particular, this work reports the variation in the solar absorptance of TiB₂/Ti(B,N)/SiON/SiO₂ coating with different angles of incidence of the solar radiation. Extensive analysis using the TEM technique reveals the presence of oxide interlayers that act as diffusion barrier layers to enhance the thermal stability of the coating. Computational simulation using SCOUT software validates the measured reflectance spectrum of the developed multilayer coating. The minor changes in absorptance and emissivity after heat treatment in vacuum at 500°C, together with high solar absorptance over a broad angular variation, establish the potential application of TiB₂/Ti(B,N)/SiON/SiO₂ as a selective coating in concentrated solar power systems.     

Prepare SiTiOC ceramic coatings by laser pyrolysis of titanium organosilicon compound

A SiTiOC ceramic coating with outstanding tribological performance was prepared by laser scanning the organosilicon coating with different laser power. The composition and structure of the obtained SiTiOC ceramic coatings were analyzed by scanning electron microscopy (SEM), infrared spectroscopy (FTIR), Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The tribological performance of the coatings was studied using a multi-functional reciprocating friction and wear tester. The results showed that the chemical structure (chemical bonding) of the coatings prepared at 0 W, 350 W, and 500 W laser powers included Si-O-Si, Si-C, and TiO₂, while that prepared at 800 W was mainly composed of amorphous SiO₂, indicating that the coating had higher ceramization. The SiTiOC ceramic coatings prepared by the present process effectively reduced the friction coefficient and wear volume of the steel substrate, which indicated that they had good anti-friction and wear resistance properties.     

Effect of titania particles preparation on the properties of Ni–TiO2 electrodeposited composite coatings

In this paper, the effect of titania particles preparation on the properties of Ni–TiO₂ electrocomposite coatings has been addressed. Titania particles were prepared by precipitation method using titanium tetrachloride as the precursor. The titanyl hydroxide precipitate was subjected to two different calcinations temperatures (400 and 900 °C) to obtain anatase and rutile titania particles. These particles along with commercial anatase titania particles were separately dispersed in nickel sulfamate bath and electrodeposited under identical electroplating conditions to obtain composite coatings. The electrodeposited coatings were evaluated for their microhardness, wettability, corrosion resistance, and tribological behavior. The variation of microhardness with current density exhibited a similar trend for all the three composite coatings. The composite coating containing anatase titania particles exhibited higher microhardness and improved wear resistance. However, the corrosion resistance of the composite coating containing commercial titania powder was superior to that of plain nickel, Ni–TiO₂ composite coatings containing anatase and rutile titania particles. The poor corrosion resistance of these composite coatings was attributed to the higher surface roughness of the coatings. This problem was alleviated by incorporating ball-milled titania powders. The composite coatings with higher surface roughness were modified with a low surface energy material like fluoroalkyl silane to impart hydrophobic and superhydrophobic properties to the coatings. Among these coatings, Ni–TiO₂–9C coating exhibited the highest water contact angle of 157°.     

Timing of polyethylene glycol addition for the control of SiO<Subscript>2</Subscript> sol structure and sol–gel coating properties

Polyethylene glycol (PEG) was added during the sol process of sol–gel SiO₂ coating preparation to investigate the effect of PEG addition timing on particle growth, sol structure, and coating properties. When PEG was added before the addition of the catalyst, the particle size increased from 10 nm (in sol without PEG) to 20 nm, and the necessary aging time for dip coating was shortened from 5 days (in sol without PEG) to ~30 h. When PEG was added 24 h later than the catalyst, the uniform sol structure and small particle unit were obtained. With the delay of the PEG addition timing to 120 h, the improvement in the homogeneity of the sol was continued, whereas the porosity of the resulting coatings decreased. The refractive index of PEG-modified SiO₂ coatings can be adjusted in a continuous range between 1.14 and 1.20, using the timing when the PEG was added. The highest peak transmittance of glass that was coated with PEG-modified silica coatings reached 99.90%. All the coatings can be changed from hydrophilic to hydrophobic after hexamethyldisilazane vapor modification.