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A new water-based silica sol was developed to provide single-layer anti-reflective (AR) coatings. The combination of nanoparticle-based aqueous coating and wiping-coating method facilitated to reduce the solvent waste. The wiping-coating process requires only 35 ml sol to cover a large glass substrate (80 × 160 cm). Samples coated on one side show an improvement in light transmission in the visible range: the maximum transmission is 95.12 ± 0.33% on float glass and 92.48 ± 0.25% on display glass. This is an excellent performance compared to the extra 99.04% maximum transmission of samples coated on both sides. The layer thickness distribution defined by the ellipsometry of 98 samples (10 × 10 cm) shows homogeneity (77.4 ± 2.2 nm) over the total area. Homogeneous films with good surface wetting were applied on glass, polycarbonate (PC), and acrylic glass (PMMA). The cured layers were successfully tested against dry heat, damp heat (40 °C/98% RH), and climatic change (−40 °C–40 °C/98% RH) on all three substrate materials. No delamination from the substrate was observed. The changes in the minimum reflection after exposure to damp heat and climatic change were minimal (ΔR = ±0.6%) in the wavelength range of 400–1000 nm. The addition of Levasil nanoparticles into the water-based silica sol improved coating hardness on glass sheets up to 3H pencil hardness without significant loss in transmission.

Sustainable production of anti-reflective coatings demands environmentally friendly approaches. This paper introduces a novel method of preparing thin films from an aqueous medium using a sol-gel technique. Single-layer anti-reflective coatings, from water-based silica sols, were prepared and characterized. The thicknesses of thin films were found to be between 75 and 135 nm with refractive indexes between 1.23 and 1.41 and porosities between 7 and 53%. The maximum transmissions of manufactured coatings reached from 99.85% to 99.03% in the visible region. The ageing of silica particles in the aqueous medium was studied using TEM. The transparent water-based sol consisted of individual silicon-dioxide nanoparticles with narrow size distribution (15–20 nm). The TEM images showed, that the silica nanoparticles become uniform and distinguishable within two weeks and no aggregation occurs within 46 days. It was found, that the aqueous silica sol is stable and clear for more than 6 months. The aqueous silica films deposited onto large glass surfaces were found to be homogeneous, with excellent adhesion (Cross Hatch Test is 0; ISO 2409 test standard) and hardness equal to 2H. We present a schematic illustration of the adsorption mechanism of non-ionic silicone surfactant and Pluronic surfactant on the silica surface.

The aim of this work was to prepare and investigate the corrosion behavior of mesoporous silica layers hosting inhibitor molecules (1H-benzotriazole, BTA and cetyltrimethylammonium bromide, CTAB), which were impregnated into the porous coatings from their aqueous solutions. The mesoporous silica layers were prepared by sol–gel dip-coating method on zinc and (for comparison) on glass substrates using two different pore-forming agents (CTAB and Pluronic PE 10,300). The permeability of one (mono-) and two (bi-) deposited layers was studied by measuring the refractive indices of impregnated samples using optical spectroscopy method. Coatings showed significant permeability to CTAB molecules regardless of the template used. Surface morphology of the samples on zinc substrates was investigated by scanning electron microscopy. The pore structure of the coatings developed with two different surfactants was studied by high resolution transmission electron microscopy. In some cases, the inhibitors were trapped in the impregnated samples by hydrophobizing the layers with dimethyldichlorosilane. Wettability of the silylated coatings was investigated by the sessile drop method. For water and an aqueous solution of Na2SO4 were obtained contact angles above 90°, which confirm the hydrophobic character of the samples. The corrosion behavior of the samples was monitored by electrochemical methods. It was found that the inhibitor containing coatings show higher corrosion inhibiting effect than the native porous silica layers. Moreover, the corrosion current densities decrease by one order of magnitude by rendering the surfaces of the inhibitor containing samples hydrophobic. Interestingly, BTA did not significantly accumulate in the pores, but its presence in the coatings caused increased protection against corrosion.

This paper presents a fast and efficient method of removing the template from silica thin films on polycarbonate. Radiofrequency-generated oxygen plasma induced the decomposition of the non-ionic surfactant. The reference samples were silica coatings on silicon, which had different pore sizes. We removed the surfactant by solvent extraction and calcination from these samples. Grazing incidence angle X-ray diffraction analysis shows a highly ordered arrangement of mesopores. The formation of the face-centred cubic structure of mesopores is independent of the substrate and the template removal method. Atomic force microscopy analysis showed open-pore channels after oxygen plasma etching. It also proved that the ammonia treatment increases the hardness of the layer. A short air-plasma treatment is effective for the consolidation of the silica layer and improves the abrasion resistance of the layer on polycarbonate. Air plasma treatment is an alternative to the long heat treatment process. We performed environmental tests according to the relevant ISO standards for optical coatings. Air plasma treated silica coatings have passed all the weathering tests. Therefore, it can be used in outdoor applications, such as a protective layer for the plastic cover of LED street lights. These thin films on polycarbonate have at least one year of service life and are weather-resistant. Plasma treatment can consolidate the silica network and the thin films on polycarbonate have high light transmission (T = 98.8 %).

We prepared mesoporous silica layers by sol-gel dip-coating technique on various substrates (silicon, polycarbonate, microscope glass and quartz) with the aid of a pore-forming triblock copolymer (Pluronic PE10500). The freshly deposited layers were aged in an aqueous ammonia solution atmosphere. Two types of thermal curing were implemented depending on the substrates: a low-temperature heat treatment at 120 °C for 13 hours or a high-temperature heat treatment at 480 °C for 1 hour. We carried out the porogen extraction of the copolymer molecules from the low-temperature heat-treated samples in a water washing step. Optical spectroscopy measurements gave evidence of a significantly improved and long-lasting light transmission of coatings. The maximum light transmission was 98.3% on glass and 97.6% on polycarbonate after 4 years of storage. TEM investigations showed thin layers with distorted face centred cubic structure. Spectroscopic ellipsometry and ellipsometric porosimetry studies showed a “two-layer” structure. The applied synthesis technique promoted the formation of a double layer structure with relatively thick (10–25 nm) pore sizes. The pseudomorphic transformation rearranged the silica/copolymer structure in presence of ammonia. The transformation was incomplete and resulted in a low porosity (23–34%) upper-layer and a high porosity (40–76%) lower-layer.

In this work, the photocatalytic properties of amorphous and crystalline TiO2 deposited on oxide and polymer nanoparticles by atomic layer deposition (ALD) were studied. Beside TiO2, as reference, both ALD grown amorphous Al2O3 and crystalline ZnO layers were also examined. When choosing the carrier, the priority was that it had no effect on the photocatalytic activity of TiO2; therefore the oxide layers were deposited on SiO2 and poly(methyl-methacrylate) (PMMA) nanoparticles. The amorphous SiO2 particles were synthetized by the Stöber method, while the PMMA particles were prepared by emulsion polymerization. Both the bare and core/shell composite nanoparticles were investigated by SEM-EDX, TEM, FT-IR, and XRD. Finally, the photocatalytic activity of PMMA, SiO2 and the core/shell nanoparticles was measured by the decomposition of methylene orange, monitored by UV-Vis spectroscopy. Based on the results, the SiO2 was uniformly coated with the deposited oxide films, while in the case of the PMMA a contiguous web-like polymer/TiO2 matrix was formed. During the photocatalytic reactions, the amorphous Al2O3 was not active, while the crystalline ZnO and TiO2 showed good photocatalytic activity. The amorphous TiO2 deposited by ALD on the SiO2 and PMMA nanoparticles had smaller, but a clearly detectable photocatalytic effect on the photodegradation of methylene orange.

Bifunctional hybrid silica sol-gel coatings were synthesized, which showed both increased light transmittance and water-repellence. The as-prepared coatings of variable thickness (100–175 nm) were found to have low refractive index (1.250–1.275), high porosity (36%–42%), and maximum light transmittance up to 99.8%. Water-repellence of the surface was due to high water contact angle (90°) and low contact angle hysteresis (1–2°). Ellipsometric porosimetry and transmission electron microscopy measurements confirmed the microporous structure of the coatings. A systematic investigation for studying the durability and the deterioration of optical and surface properties was studied during aqueous soaking tests at different pH. During these experiments atomic force microscopy showed that the morphology of the surface did not change. The changes in the wetting properties were also confirmed by surface free energy measurements and an increase of the polar component was observed. The optical properties could be regenerated completely or partially after the soaking via heat treatment at 400 °C. The light transmittance of the samples remained high after the soaking, most likely due to the swelling of the solid matrix. The light transmittance and the water-repellent properties of the coatings showed long-term stability up to a year of storage.

Silica sol-gel coatings on different substrate materials and their use as model systems have been studied. Mesoporous silica coatings with thicknesses of 85 - 135 nm and porosity of 18 ˗ 37% were prepared by dip-coating on polycarbonate and glass substrates. In order to eliminate the shrinkage of the porous structure acid or base vapour treatment was applied. Thickness and refractive index of the coatings were determined by analysing the transmittance spectra of the samples. Ellipsometric porosimetry measurements were carried out to determine the porosity, pore radius distribution, thickness and refractive index. The thickness of the samples was further confirmed by scanning electron microscopy. The adsorption capacity of the porous coatings was also studied by dye impregnation tests. The temporal stability of the samples was investigated by UV-Vis spectrometry and it was found that the advantageous optical properties (Tmax = 98 – 99%) of the samples remained constant even after a 1 year storage period.

The structures of glycine·H2O complexes have been reinvestigated in low-temperature inert matrices. To go beyond the former matrix-isolation IR studies, NIR laser irradiation was used to change the relative abundances of the different complexes in the matrix. It is shown that the irradiation of the first overtone of the OH stretching mode of glycine as well as of the first overtone of the OH stretching mode of the water molecule in the complex can induce structural changes. Comparison of the experimental IR spectra with the IR spectra computed for different structures resulted in more reliable assignments of spectral patterns and identification of more structures than in former studies.