Sol-Gel Coatings for Subaquatic Self-Cleaning Windows (original) (raw)
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Applied Optics
Double layer thin films, mechanically stable and adhering to glass, were produced through the sol-gel process, using tetraethyl orthosilicate and titanium butoxide as precursors. The refractive index of the titania and silicatitania composite layers were typically 2.1 and 1.7, and their physical thicknesses were approximately 65 nm and 81 nm, respectively, as determined by ellipsometry. These optical constants allowed attainment of quarterwave optical thicknesses at the center of the visible spectrum (550 nm) as designed, with an increase of 3.4% in transmittance. The nanometric surface roughness, measured by optical profilometry, was effective to decrease light scattering and water contact angles to below 10 •. As novelty in dip-coated sol-gel films, superhydrophilicity for self-cleaning, antifogging, and antireflection in the mid-visible spectrum were simultaneously attained with durability of 9 weeks in the dark. Further application of UV light allowed regeneration of contact angles for self-cleaning.
Progress in Organic Coatings, 2019
A sol-gel coating using colloidal silica on a glass surface is carried out towards improving the self-cleaning properties. The optical transmittance and hydrophobic characteristics of the resulting coating are analyzed using analytical tools. Since the sol-gel coating reduces the optical transmittance of the glass samples, due to scattering and diffusion of the incident optical radiation at the coating surface, silicon oil (Sigma-Aldrich, 10 cSt) impregnation method is introduced to improve the optical transmittance. Silicon oil has good heat transfer characteristics, stable properties over range of temperatures, and optically transparent characteristics with refractive index of 1.4034. The resulting coated surface is tested in outdoor environments to examine the dust effect on the optical transmittance of the sol-gel coated and oil impregnated glass samples. It is found that deposition of 75 nm size silica particles on the glass surface modifies the texture height of the sol-gel coating, which in turn, improves the surface hydrophobicity. Sol-gel coating results in a web-type fully connected porous structures; in which case, agglomeration of the synthesized particles is responsible for the fully connected porous texture at the coating surface. The optical transmittance remains low for the sol-gel coated glass samples because of scattering and diffusion of the incident optical radiation at the coating surface. Silicon oil impregnation improves the optical transmittance of the sol-gel coated samples. The dust particles immerse into the oil film and reduce the optical transmittance of the oil impregnated samples in outdoor environments.
Materials, 2019
The number of commercial products claiming self-cleaning properties is rising and testing of long-term activity and durability of such coatings needs to be addressed more. The time-dependent changes of different characteristics like haze, transparency, and color are essential for transparent glazing materials. Herein, we aimed to examine whether the laboratory results obtained on the Zr-modified-titania-silica (TiZr) self-cleaning materials would translate to larger-scale outdoor-exposed testing. TiZr thin films were deposited via spraying onto float glass window surfaces and exposed into three different environments for 20 months. For comparison, a commercially available active SGG BIOCLEANTM glass and standard float glass were simultaneously exposed in the same conditions. It was shown that the self-cleaning property of either a commercial product or TiZr-coated float glass was not considerably effective in real field test conditions, although the previous laboratory tests showed ...
Self-cleaning antireflective optical coatings – Supporting Information
Low-cost antireflection coatings (ARCs) on large optical surfaces are an ingredient-technology for high-performance solar cells. While nanoporous thin films that meet the zero-reflectance conditions on transparent substrates can be cheaply manufactured, their suitability for outdoor applications is limited by the lack of robustness and cleanability. Here, we present a simple method for the manufacture of robust self-cleaning ARCs. Our strategy relies on the self-assembly of a block-copolymer in combination with silica-based sol–gel chemistry and preformed TiO2 nanocrystals. The spontaneous dense packing of copolymer micelles followed by a condensation reaction results in an inverse opal-type silica morphology that is loaded with TiO2 photocatalytic hot-spots. The very low volume fraction of the inorganic network allows the optimization of the antireflecting properties of the porous ARC despite the high refractive index of the embedded photocatalytic TiO2 nanocrystals. The resulting ...
Solar Energy Materials and Solar Cells, 2010
The development of novel multifunctional coatings plays a crucial role in the achievement of more competitive architectural glasses and glazing materials for solar applications, among others. In this respect, coatings that provide high transmittance together with self-cleaning capacity could mean an added value to such glasses and glazing materials. Herein we report design and preparation of novel multifunctional (MF) coatings that present anti-reflection (AR) and self-cleaning (SC) capacity. First of all, preparation conditions of AR and SC coatings were optimized separately. The nano-structure and film thickness were carefully controlled by the solvent and the template agent ratio, in order to direct the refraction index and transmittance of each layer. Acquired experience allowed the fabrication of MF coatings consisting of two-layer stacks with a mesoporous SiO 2 AR layer and a dense/mesoporous TiO 2 layer. Regarding the anti-reflection capacity, MF and AR coatings present a net solar transmittance of 95.9% and 96.6%, respectively. Photocatalytic evaluation of the prepared SC and MF coatings showed that the mesoporous TiO 2 layers can reach a higher photodegradation degree of organic matter than dense TiO 2 layers. It is worth mentioning that the synergy between the AR and SC layers, promote a marked enhancement of the self-cleaning capacity of the MF coatings, exceeding in a 25-30% the photodegradation degree achieved with the commonly used porous or compact TiO 2 coatings.
Multifunctional bioinspired sol-gel coatings for architectural glasses
Building and Environment, 2010
Although several multinational companies have recently released products incorporating bioinspired functional coatings, their practical integration in building envelopes is still an open issue. High production costs associated to the existing vacuum deposition technologies, as well as the difficulties in extending the number of functions achievable by a single coating, represent to date the main limitations to their diffusion on a large scale. This review summarizes the key topics in the field of functional coatings for architectural glasses, focusing in particular on the potential applications of sol-gel based antireflective and self-cleaning coatings, that have received a tremendous attention in the last years. It provides an overview of the recent research efforts aimed to improve their properties and to extend their range of applicability. The bioinspired principles, upon which such coatings are based, are also described and are related to the chemical and morphological properties of such surfaces.
Sol-gel thin films with anti-reflective and self-cleaning properties
Chemical Papers, 2012
Self-cleaning photocatalytic TiO2 films are beneficial since they reduce the maintenance cost and enhance the efficiency of various optical systems, especially thermal and photovoltaic solar systems. However, the presence of a TiO2 layer on glass reduces the transmission of incident light, which leads to a decrease in efficiency. This drawback can be overcome by applying a layer of anti-reflective coating beneath the TiO2 layer. Generally, the anti-reflective layer is porous silica. The presence of the anti-reflective layer compensates for the loss of light transmittance caused by the photocatalytic TiO2 top layer. This paper reviews some of the previous and the latest fundamental studies in the literature on anti-reflective, self-cleaning and multi-functional films.
Self-Cleaning Antireflective Optical Coatings
Nano Letters, 2013
Low-cost antireflection coatings (ARCs) on large optical surfaces are an ingredient-technology for high-performance solar cells. While nanoporous thin films that meet the zero-reflectance conditions on transparent substrates can be cheaply manufactured, their suitability for outdoor applications is limited by the lack of robustness and cleanability. Here, we present a simple method for the manufacture of robust selfcleaning ARCs. Our strategy relies on the self-assembly of a blockcopolymer in combination with silica-based sol−gel chemistry and preformed TiO 2 nanocrystals. The spontaneous dense packing of copolymer micelles followed by a condensation reaction results in an inverse opal-type silica morphology that is loaded with TiO 2 photocatalytic hot-spots. The very low volume fraction of the inorganic network allows the optimization of the antireflecting properties of the porous ARC despite the high refractive index of the embedded photocatalytic TiO 2 nanocrystals. The resulting ARCs combine high optical and self-cleaning performance and can be deposited onto flexible plastic substrates.
Visible and near infrared, wide-angle, anti-reflection coatings with self-cleaning on glass
Optical Materials Express, 2012
In this work self-cleaning and transparent surfaces were produced on glass surface with simultaneous wide-angle and good optical transmittance on the visible region. These properties are pursued by combination of multi-scale surface topology based on silica nanoparticles (SNPs), index grading and interference coating, as well as polytetrafluoroethylene (PTFE) self-assembly, using two approaches. In the first, two-layer approach (glass/SNPs/PTFE), the resulting samples presented a water contact angle (WCA) of 169° ± 2° with very low hysteresis, as well as significant antireflection. The second, three-layer approach (glass/SNPs/silica aerogel/PTFE), produced surfaces with WCA of 158° ± 2° with also very low hysteresis (<5°), in addition to normal transmittance of 99% or higher, which decreased less than 2% at 20° incidence. These results show that proper structure-coated glass, with a combination of interference and graded-index effects, may provide simultaneous wide-angle antireflection and self-cleaning properties.