Modified Silica Coatings Research Articles

Porous silica coating with excellent atomic oxygen protection performance and flexibility

With the rapid development of spacecrafts in the low earth orbit (LEO), the protection requirements of polyimide (PI) surface against atomic oxygen (AO) erosion had been highlighted. Inorganic coatings trended to crack and peel off due to stress, which limited their application on flexible polymer surfaces. Different from the conventional idea of using dense inorganic coatings to develop AO resistance, in this work, APTES ((3-aminopropyl) triethoxysilane) -modified silica coatings with porous structure have successfully removed the influence of stress and increased the adsorption of AO and adhesion. As a result, the porous silica coating exhibited excellent AO protection performance (low erosion of 1.18 × 10−26 cm3 atom−1), good flexibility (no damage or crack on the surface after bending), and enhanced PI substrate-adhesion. The results of first-principles calculations and experiments indicate that the structure with large surface area and small pore volume is able to adsorb AO and reduce the erosion. This study proposed a new solution of adopting non-dense structure and a novel AO protection mechanism of porous coatings, which expands the application of inorganic coatings for AO protection.

The effect of surface chemistry on anti-soiling properties of transparent perfluoroalkyl and alkyl modified silica coatings

Various physical and chemical surface parameters, e.g., surface roughness and surface chemistry, contribute to anti-soiling (AS) properties. Nevertheless, the effect of surface chemistry has not been distinctly elucidated yet. In this study, a set of mechanically stable and durable hydrophobic AS coatings with controlled surface chemistry were synthesized, while surface roughness was kept below 1 nm. Fluoroalkylsilane (FAS), alkylsilane (AL), and tetraethyl orthosilicate (TEOS) were employed for synthesis. Surface chemistry and surface roughness were quantified by XPS and AFM. A soiling lab simulator was designed to accelerate the soiling process. AS properties were quantified by UV–vis spectroscopy and optical microscopy. The surface free energy of coatings was estimated through (polar and apolar liquids) contact angle measurements (ranging from 16 to 30 mN/m), and a clear correlation was discovered between the AS properties and surface free energy. Moreover, mechanical properties and weathering resistance of the coatings were analyzed by nano-indentation and QUV accelerated weathering tester. While all coatings showed acceptable AS properties (transmission loss after dust deposition between 1/5 and 2/5 of uncoated glass) and excellent mechanical strength (above 27 GPa modulus and 2 GPa hardness), FAS-based coatings showed a significantly higher durability against weathering as compared to the AL-based ones.

Preparation and Characterization of Some Sol-Gel Modified Silica Coatings Deposited on Polyvinyl Chloride (PVC) Substrates

Transparent and antireflective coatings were prepared by deposition of modified silica materials onto polyvinyl chloride (PVC) substrates. These materials were obtained by the sol-gel route in acidic medium, at room temperature (25 °C), using different alkoxysilanes with various functional groups (methyl, vinyl, octyl or hexadecyl). Physicochemical and microstructural properties of resulted silica materials and of thin coatings were investigated through Fourier Transforms Infrared Spectroscopy (FTIR), UV-Vis spectroscopy, Thermal Gravimetric Analysis (TGA), Dynamic Mechanical Analysis (DMA), Atomic Force Microscopy (AFM) and ellipsometric measurements. Wetting behaviors of the silica coatings were evaluated by measurement of static contact angle against water. FTIR spectra of materials confirmed the high degree of cross-linking that result from the formation of the inorganic backbone through the hydrolysis and polycondensation reactions together with the formation of the organic network. These sol-gel silica coatings showed a reduction in the reflectance (10%) compared with uncoated PVC substrate. AFM reveals that the films are uniform, and adherent to the substrate, but their morphology is strongly influenced by the chemical composition of the coating matrices. These silica coatings can be useful for potential electronic and optical devices.

Preparation and Anticorrosive Properties of Oligoaniline Modified Silica Coatings

Novel trianiline-containing sol-gel hybrid coatings were prepared by one-step electrodeposition technology on the surface of Q235 steel. The chemical component, microstructure of the as-prepared coatings were measured by FTIR, UV-vis, SEM. The effects of deposition time on the thickness, contact angle (CA) and surface roughness of coatings were investigated. The results showed that the modified silica coatings exhibited an excellent hydrophobic nature. By comparing with various deposition times (100, 300, 500, 700 s) under the deposition potential of -1.5 V, the coating under the deposition time of 500 s presented the best anti-corrosion effectiveness for bare steel substrate in 3.5 wt.% NaCl solution as verified by Tafel curves and electrochemical impedance spectroscopy (EIS).

Methyl–modified hybrid organic-inorganic coatings for the conservation of copper

Abstract A simple sol-gel technique for the preparation of methyl–modified silica coatings for the protection of the external surface of copper has been used in this study. Tetraethylorthosilicate (TEOS) has been used as a precursor to prepare nanosilica coatings on the surface of copper. The methyl–modified silica sols were obtained by mixing of 3% SiO2 sol solution with trimethylchlorosilane (TMCS) or hexamethyldisilozane (HMDS) as basic materials. For comparison, the copper substrates were also coated with commercial polymers (Paraloid B 72, Plexisol P 550-40 and polyvinyl butyral (PVB)). The surface morphology changes of uncoated and coated specimens were investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The hydrophobicity of surfaces and photochemical ageing effects were evaluated by contact angle measurements. Potentiodynamic measurements were obtained in order to compare corrosion parameters of the coatings.

Organically modified silicas on metal nanowires.

Organically modified silica coatings were prepared on metal nanowires using a variety of silicon alkoxides with different functional groups (i.e., carboxyl groups, polyethylene oxide, cyano, dihydroimidazole, and hexyl linkers). Organically modified silicas were deposited onto the surface of 6-μm-long, ∼300-nm-wide, cylindrical metal nanowires in suspension by the hydrolysis and polycondensation of silicon alkoxides. Syntheses were performed at several ratios of tetraethoxysilane to an organically modified silicon alkoxide to incorporate desired functional groups into thin organosilica shells on the nanowires. These coatings were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy. All of the organically modified silicas prepared here were sufficiently porous to allow the removal of the metal nanowire cores by acid etching to form organically modified silica nanotubes. Additional functionality provided to the modified silicas as compared to unmodified silica prepared using only tetraethoxysilane precursors was demonstrated by chromate adsorption on imidazole-containing silicas and resistance to protein adsorption on polyethyleneoxide-containing silicas. Organically modified silica coatings on nanowires and other nano- and microparticles have potential application in fields such as biosensing or nanoscale therapeutics due to the enhanced properties of the silica coatings, for example, the prevention of biofouling.

Antimicrobial coatings on textiles–modification of sol–gel layers with organic and inorganic biocides

Antimicrobial textile materials were produced by sol–gel coatings with embedded biocidal compounds. For preparation a sol–gel procedure was used, starting from pure silica sols and 3-glycidyloxypropyltriethoxysilane (GLYEO) containing silica sols. These sols were modified with silver compounds, hexadecyltrimethyl-ammonium-p-toluolsulfonat (HTAT) and copper compounds, respectively. The investigations were performed on viscose fabrics as function of the concentration of biocidal compounds and of thermal treatment of textile after dip-coating between 80 up to 180 °C. The use of modified silica coatings leads to a decreased growth of fungi (Aspergillus niger) and bacteria (Bacillus subtilis and Pseudomonas putida) with increasing amount of the biocide embedded in the coating. The addition of GLYEO supports the biocidal effect of the coatings and enhances the stability of the coating solutions. For preparation of antimicrobial silica coatings the biocides silver, copper or HTAT can be used alone but the combination of these compounds leads to enhanced results against both fungi and bacteria. Therefore silica sols containing a combination of different types of biocides may be used for antimicrobial modification of textiles in some practical applications. For industrial applications the here presented coating solutions are especially advantageous, because of 90% water content in the solvent.

Immobilization of alkaline phosphatase on modified silica coatings

The immobilization of a model enzyme, alkaline phosphatase (ALP), onto differently modified silica surfaces and coatings was investigated as a test case for the biofunctionalization of implant surfaces. In this context, the influence of silica surface structures and various silane linker molecules on the capacity to bind active proteins were studied. For this purpose, microscope glass slides were coated with unstructured or mesoporous silica films. The binding of the protein to the surface was mediated by trialkoxysilanes with different functional groups like amino, epoxy, and urea functions. The model protein ALP was chosen due to its robustness and the availability of a simple activity assay. This assay showed that all the functionalized trialkoxysilanes tested were able to immobilize active ALP on silica surfaces. Using the 3-aminopropylsilyl modification resulted in the highest activity of bound ALP, especially in combination with a mesoporous surface coating. Interestingly, unstructured silica sol–gel films had only low capacity to immobilize active enzyme whereas both mesoporous silica coatings and plain glass bound higher amounts of active ALP. By using mesoporous coatings functionalized with 3-aminopropylsilyl residues, maximal binding capacities for active ALP were achieved. This combination appears most promising for the further development of bioactive surfaces for practical applications such as surgical implant functionalization.

Bioactive textiles by sol–gel immobilised natural active agents

The sol–gel immobilisation and controlled release of various bioactive liquids (BL) from within modified silica coatings were investigated, in order to evaluate the suitability of functionalised textiles for the following applications: (1) skin-friendly textiles with antimicrobial and antiallergic effects due to immobilised natural oils such as evening primrose and perilla oil; (2) textiles for therapeutic treatment of the respiratory tract by means of immobilised mixtures of high volatility natural agents such as eucalyptol, camphor and menthol. Results indicating the antimicrobial properties, washfastness and medical activity of the bioactive textiles are presented. Of note is the transdermal resorption of the BL from the sol–gel coated textiles, determined by the time-dependent concentration of cineol, camphor and menthol in the air exhaled by test subjects after the application of coated textiles. When compared to the application of an ointment, not only does the use of coated textiles offer a more continuous and prolonged release of the embedded BL, but it is also more convenient.

Sol?Gel Synthesis of Methyl Modified Optical Silica Coatings and Gels from DDS and TEOS

Methyl modified silica coatings and gels were prepared from dimethyldiethoxysilane and tetraethylorthosilicate via sol–gel processing and spin-coating. The as-synthesized coatings showed not only anti-reflectivity but also hydrophobicity and high laser damage thresholds compared to pure silica coatings without methyl modification. The existence of methyl groups in the framework was demonstrated by IR and NMR spectroscopy. The microstructure of the xerogels obtained were also characterized and will be discussed.

Antimicrobial Sol?Gel Coatings

The preparation and the releasing behavior of modified silica coatings, containing embedded biocides on textiles, were compared and assessed with regard to application parameters like antimicrobial efficacy, wash-out and long-term behavior. For this, silica layers with embedded silver, silver salts and biocidal quaternary ammonium salts (cetyltrimethylammoniumbromid and octenidine) were investigated. Both the growth of fungi and bacteria can be inhibited by coatings with embedded biocides. Especially by using octenidine, an excellent long-term inhibition of fungi growth can be reached.