Base-catalyzed Silica Sols Research Articles

Highly transparent and stable luminescent films with stable europium (III) complex Assisted with anti-Reflective coating

Rare earth complex polymer luminescent materials have important practical application value in organic electroluminescence, fluorescence sensing, solar cells and other fields. Herein, we fabricated the luminescent film (recorded as Eu (2 mCND)4Na/PMMA@LF) through doped Eu (2 mCND)4Na complex with polymethyl methacrylate (PMMA) followed by coating on a PMMA slab. And the antireflective (AR) coatings prepared with acid-catalyzed silica sol (ACSS) and base-catalyzed silica sol (BCSS) were coated on the surface of Eu (2 mCND)4Na/PMMA@LF which enhance its transparency increasing from 92 % to 98.7 %. This is because that the AR coatings have high transmittance and environmental stability. In addition, the luminescent film coated with antireflective coating displays high photo-stability, which was also demonstrated after a 35 h UV LED (∼200 mW/cm2) irradiation. The configuration of luminescent film with anti-reflection performance provides a scalable alternative to the current approaches for creating highly transparent solar windows.

Durable superhydrophilic and antireflective coating for high-performance anti-dust photovoltaic systems

Antireflection coatings have received extensive attention due to their unique ability to reduce the reflection losses of incident light in photovoltaic (PV) systems. In this study, we report a hybrid silica sol coating fabricated via a simple and cost-effective base/acid-catalyzed two-step sol–gel method. The prepared coating exhibits these main properties: high transmittance, superhydrophilic, and anti-dust effect. Experimental conditions to achieve high transmittance were systematically optimized, such as aging time of the base-catalyzed silica sol and dip-coating speed. A transmittance improvement of about 6.35% compared to the bare glass substrate was then obtained. The morphology and film structure were also characterized. The coatings have a closed and dense structure which, combined with their superhydrophilicity, endowed them with excellent anti-dust performance, as well as high mechanical properties, with a pencil hardness of 4H. Furthermore, the coating showed great resistance to high temperature and high humidity as well as high stability to long-time outdoor exposure. The results suggest the good reliability of the prepared coatings for PV solar glass application.

An ORMOSIL porous double-layer broadband antireflective coating

A λ/4–λ/4 broadband antireflective (AR) coating is developed with a sol-gel dip-coating method. By adding SAR-5 organosilicon resin into a base-catalyzed silica sol top layer and treating at 300°C, a broadband AR coating used for blast shields with a high average transmission of 99.34% (450–950 nm) and good hydrophobicity (with a water-contact angle of 119°) was obtained. After being subjected to rubbing 50 times and being maintained at a relative humidity of around 95% for 50 days, the average transmission of the coating decreased by 0.29% and 0.04%, respectively. This indicates that the organically modified silica (ORMOSIL) broadband AR coating has good abrasion resistance and humidity stability.

Double-layer tri-wavelength hydrophobic antireflective coatings derived from methylated silica nanoparticles and hybrid silica nanoparticles

In this paper, we reported the design and preparation of a double-layer antireflective (AR) coating, which possessed relatively high transmittance at 351, 527, and 1053 nm. The refractive indices and film thicknesses of the under layer and upper layer of the simulated AR coating were determined as 1.27, 95 nm and 1.18, 106 nm, respectively. The under layer of the double-layer coating dip-coated from a mixture of base-catalyzed and acid-catalyzed silica sols had a refractive index of 1.27. The upper layer fabricated by the deposition of methylated silica nanoparticles by simply adding methyltriethoxysilane into the base-catalyzed silica sols possessed a refractive index of 1.18. The hydrophobicity of coatings could be dramatically improved with the water contact angle increasing from 23.4° to 150.0°, and the refractive indices of the pure base-catalyzed silica coatings were easily decreased from 1.20 to 1.12 through the surface treatment of silica nanoparticles. Thus, we have successfully prepared a double-layer AR coating, which had a high transmittance of 99.8%, 96.1%, and 99.7% at 351, 527, and 1053 nm, respectively.

Preparation of hydrophobic broadband antireflective SiO2 coating on flexible poly(methyl methacrylate) substrates

The double-layer broadband antireflective coatings is crucial for optical devices, e.g. plastic eyeglass lenses and the solar cell system. Among optical situation, the wide wavelength range of light is one of the most demanded. Here we designed a double-layer broadband antireflective (AR) coating with excellent average transmittance at visible region for poly (methyl methacrylate) (PMMA) using thin film design software. A template-free sol–gel process was developed to prepare the SiO2/PMHS coating with ultralow refractive index of 1.13 for top layer. By combining the colloidal silica and poly (methyl hydrogen) siloxane (PMHS), the coating with adjustable refractive index that vary between 1.13 and 1.37 was obtained. The formation mechanism of the ultralow refractive index was proposed. Meanwhile, using PMHS to partially substitute the hydrophilic groups in the coating, the hydrophobicity of the coatings was improved, and its static water contact angle was as high as 126°. Besides, the coating had excellent mechanical property and refractive index of 1.22–1.42 can be well prepared by combining base-catalyzed silica sol and acid-catalyzed silica sol together for bottom layer. Then, using the two raw materials base/acid -catalyzed mix SiO2 sol and the PMHS-SiO2 sol and optimizing the thickness, the prepared double-layer coatings with average transmittance of 99.30% in the 400nm to 800nm wavelength on PMMA substrate was successfully obtained. Those prepared hydrophobic broadband AR coatings represented excellent transmittance and had enormous potential application in the optical devices.

SiO2–ORMOSIL double-layered broadband antireflective coating for high-power laser system

Broadband antireflective (AR) coating for high-power laser system has been realized by depositing double-layered SiO2–ORMOSIL thin films onto fused silica substrates. The refractive indices of bottom and top layers are 1.29 and 1.13, respectively. The top layer was composed of an ORMOSIL thin film which was prepared by a template-free sol–gel process by hybridization of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS). The hybridization of TEOS and DDS decreased gradually the refractive indices of ORMOSIL thin films from 1.21 to 1.13 as the molar ratio of DDS to TEOS increased from 0.0 to 0.8. The bottom layer was prepared by hybridization of acid-catalyzed and base-catalyzed silica sols. Finally, the double-layer broadband AR coating with transmittance of 100.0 and 99.9 % at 1064 and 532 nm, respectively, was realized. The laser-induced damage threshold (LIDT) of double-layer double-wavelength AR coating is 48.8 J cm−2. This double-layer SiO2–ORMOSIL AR coating possessed excellent transmittance at simultaneously 1064 and 532 nm, good AR stability and high LIDT, and will find important application in high-power laser system.

Preparation of SiO<sub>2</sub> Antireflective Film by a Base/Acid Two-Step Catalyzed Sol-Gel Process

SiO2 antireflective films were prepared by two-step catalyzed sol-gel method with TEOS as the raw materials, acid and ammonia as catalyst. Effects of the ratio of acid-catalyzed and base-catalyzed silica sols on the transmittance and stability of SiO2 film were investigated. The transmittance can be adjusted by change the ratio of base-catalyzed sols, and a higher transmittance can be obtained in the higher ratio of base-catalyzed coatings. A higher stability of SiO2 film in salt spray can be obtained in higher ratio of acid-catalyzed AR coatings. AR coatings with excellent transmittance and stability can be obtained by adjusting the ratio of acid/base catalyzed silica sols.

Improvement in Mechanical Property of SiO2 Films Prepared by Sol-Gel

Silica films prepared by the base catalyzed sol–gel process show poor mechanical property. In this study, silica anti-reflective films with good mechanical property have been prepared by the catalyzed sol–gel process with dimethyl formamide added as drying control chemical additives. The silica sol was first dip deposited onto substrate to form films on both sides of the substrate and then subjected to thermal treatment. After thermal treatment, the film was achieved due to the formation of porous structure in the resultant film as a result of decomposing tetraethylorthosilicate and dimethyl formamide. Nano-indenter measurement shows that the Young’s modulus and hardness of base catalyzed films are 10-20GPa and 0.25-0.55GPa, respectively. But the films added with dimethyl formamide are much better than those films derived from base-catalyzed silica sols, the Young’s modulus and hardness are 32-39GPa and 1.22-1.47GPa, respectively. The good mechanical properties make such films potential in both military and civil applications.

Synthesis of silica-coated graphite by enolization of polyvinylpyrrolidone and its thermal and electrical conductivity in polymer composites

Silica-coated graphite flakes, which have electrical insulating property and high thermal conductivity, were synthesized by a polyvinylpyrrolidone (PVP)-assisted sol–gel reaction. The critical role of keto-enol tautomerism of PVP in base-catalyzed silica sol–gel reaction was elucidated. The degree of silica coating on graphite was controlled by the amount of PVP and silica precursor, tetraethyl orthosilicate. The silica-coated graphite was used as a filler in thermoplastic polyester elastomer (TPEE). The in-plane (Λ) and through-plane (Λ⊥) thermal conductivity values of silica-coated graphite/TPEE composites are 67.5% and 86.6% of those of raw graphite/TPEE at 80phr loading. Even after a severe mixing process under high shear at elevated temperature, silica-coated graphite/TPEE composites retain the perfectly insulating surface resistivity of >1013Ω/sq up to high filler contents.

Sol–gel preparation of double-layer tri-wavelength antireflective coating

Double-layer tri-wavelength antireflective (AR) coating effective simultaneously at 351, 527 and 1,053 nm has been designed and prepared by the sol–gel process. The refractive index and film thickness of bottom layer and up layer are 1.27 and 113 nm, and 1.17 and 245 nm, respectively. The bottom layer with refractive index of 1.27 was prepared from a mixture of acid-catalyzed and base-catalyzed silica sols, and the up layer with refractive index of 1.17 was prepared from polypropylene oxide modified silica sol. It was found that the addition of polypropylene oxide into the sol significantly decreased the refractive index and increased the hydrophobicity of the AR coating. The obtained tri-wavelength AR coating gives very high transmittance of 99.7, 99.1 and 98.0 % at 351, 527 and 1,053 nm, simultaneously.

Novel pathways for the preparation of silica antireflective films: Improvement in mechanical property

Silica antireflective films by the base catalyzed sol–gel process show poor mechanical property. In this study, silica antireflective films with good mechanical property have been prepared by the acid catalyzed templating sol–gel process. The single-layer film was deposited from an acid-catalyzed silica sol solution with polymer F127 incorporation. The silica sol was first dip deposited onto substrate to form films on both sides of the substrate and then subjected to thermal treatment at 500 °C. After thermal treatment, the abrasion resistant antireflective film was achieved due to the formation of porous structure in the resultant film as a result of decomposing F127. Optical spectroscopic measurement shows that the coated glass with maximum transmittance of 99.5% has been obtained. Nanoindenter measurement shows that the elastic modulus and hardness of films are 16 GPa and 1.3, respectively, which are much better than those films derived from base-catalyzed silica sols. The high transmittance and good mechanical property make such films potential in both military and civil applications.

Laser-induced damage mechanism of the sol–gel single-layer SiO2 acid and base thin films

Sol–gel single-layer silica acid and base thin films on K9 glass substrates were prepared with the dip-coating method from acid and base catalyzed silica sols, respectively. Laser-induced damage threshold (LIDT) of each film was measured. Properties of the films were analyzed using Stanford photo-thermal solutions (SPTS), ellipsometry, atomic force microscopy (AFM) and optical microscopy to study the damage mechanism of the films under laser irradiation. The experimental results showed that compared with the silica base film, the silica acid film had larger absorption and smaller porous ratio, and it had smaller LIDT. The different damage morphologies of films were influenced by their different absorption and microstructure characteristics. The silica base film is more suitable for applications involving high power lasers.