A scratch-resistant single-layer antireflective coating by a low temperature sol-gel route (original) (raw)
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Thin Solid Films, 2014
Scratch resistant silica-based hybrid coatings on polycarbonate substrates were formed by dip-coating of acidcatalyzed tetramethyl ortohosilicate (TMOS):diethylenetriamine (DETA):H 2 O:2-propanol sols. The sol formulation and dip-coating process parameters on microstructural and performance properties-here optical transmittance and scratch resistance-of the coatings were evaluated. The effect of water quantity, total aqueous component (H 2 O + 2-propanol) amount and relative proportion of TMOS:DETA on film formation behavior and on performance properties have been investigated in a systematic way. It was found that an effectively polymerized hybrid coating rich in silica content, as realized for high TMOS or abundant water containing sols, resulted in defective films with microcracking and adhesion problems. High 2-propanol content on the other hand led to incomplete film coverage. It was shown that 5 ± 1 μm-thick, scratch resistant and pristine coatings exhibiting a visible transmittance of 86-88% can be formed with a single deposition process using an optimized sol formulation of TMOS:DETA:H 2 O:2-propanol of 30:30:20:20 in wt.%. Meanwhile, the hardness of the PC has increased from an initial value of 13.9 ± 2 to 70 ± 25 (Vickers hardness, HV1) upon coating. A surface hardness approaching to 250 HV1 can be attained by for the thicker coatings (8 ± 1 μm) deposited at higher withdrawal speeds. However, such films suffered from non-uniform coverage and poor surface/optical quality. The transmittance values reduced by a factor of 20-30% for thicker coatings.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018
We report the fabrication of nanoporous silica coatings with tunable refractive indices by a one-step basecatalyzed sol-gel process using tetraethoxysilane as the precursor, hexamethylisilazane as the modifier at ambient conditions. The advantages of the present method are inexpensive, etchant-free and without high temperature calcination treatment. Importantly, porosity of the coatings can be tunable by changing the monomer ratio of the starting solution, which makes them suitable for top layer of broadband AR coatings. The tri-wavelength broadband AR coating with the refractive indices of the bottom and top layers as 1.27 and 1.16 was achieved on a fused silica substrate, which possessed high transmittance of 99.6%, 98.0% and 99.3% at 351 nm, 527 nm and 1053 nm, respectively. Moreover, the double-layer coating showed significant stability, when tested with polydimethylsiloxane pollution in vacuum for a week. In addition, LIDT of the double-layer coating was up to ca. 19.0 J cm −2 at a 6.3 ns laser pulse of 351 nm wavelength. This double-layer AR coating possesses excellent broadband AR performance, high LIDT, and excellent vacuum stability, which can open a new avenue to explore applications in high-power laser systems.
Sol-gel Derived Optical Coating with Controlled Parameters
The optical properties and structure of antireflective coatings (AR) deposited from hydrolysed TEOS sol were characterized in detail in this study. The influence of different parameters on the formation of colloidal silica antireflective coatings by dip-coating technique has been investigated. For the characterization of colloidal silica films the UV-visible spectroscopy, laser ellipsometry and atomic force microscopy were used. Using optimal sol-gel processing conditions (dipping rate – 40 mm/min, coating time – 20 s, and temperature – 20 °C) the colloidal silica coatings were obtained and characterized in comparison with non-coated glass substrate. The reflectance of AR coatings increases with increasing the temperature of sol-gel processing. The Nd:YAG laser damage threshold of AR coating exceeded 15.22 J/cm 2 at 1064 nm and 26.82 J/cm 2 at 355 nm.
Antireflective Coatings for Glass and Transparent Polymers
Langmuir, 2016
Antireflective coatings (ARCs) are applied to reduce surface reflections. We review coatings that reduce the reflection of the surface of the transparent substrates float glass, polyethylene terephthalate, poly(methyl methacrylate), and polycarbonate. Three main coating concepts exist to lower the reflection at the interface of a transparent substrate and air: multilayer interference coatings, graded index coatings, and quarter-wave coatings. We introduce and discuss these three concepts, and zoom in on porous quarter-wave coatings comprising colloidal particles. We extensively discuss the four routes for introducing porosity in quarter-wave coatings through the use of colloidal particles, which have the highest potential for application: (1) packing of dense nanospheres, (2) integration of voids through hollow nanospheres, (3) integration of voids through sacrificial particle templates, and (4) packing of nonspherical nanoparticles. Finally, we address the remaining challenges in the field of ARCs, and elaborate on potential strategies for future research in this area.
Tribology of water and oil repellent sol–gel coatings for optical applications
Wear, 2009
Oil and water repellent sol-gel silica coatings may be used to extend the use and lifetime of certain computer displays, optoelectronic devices, and optical components such as touch screens. Organic-inorganic coatings consisting of organically modified silica are an optimal class of materials to use for such applications as they are substantially more durable than conventional polymers while having low processing temperatures compatible with organics. This study is concerned with the characterization of wear-resistant coatings derived from polysiloxanes. Organically modified sol-gel silica coatings were deposited on soda-lime glass substrates by dip coating. Mechanical, surface, and tribological properties were investigated using nanoindentation, contact angle goniometry, stylus profilometry, and a reciprocating polishing wear test to determine wear rate by mass loss. The average hardness of films was found to be 1.2 GPa and independent of curing times above 30 min at 150 • C. In polishing wear, failure was caused by gradual abrasive wear through the depth of the coating. Wear rate was found to be independent of curing times above 30 min at 150 • C. The development of these coatings will contribute to the rational design of the next generation of transparent overlays and displays.
Journal of Coatings Technology and Research, 2016
We describe novel optical coatings which require either thermal or photocuring to render them mechanically robust and abrasion resistant. These new coatings are low refractive index fluoroelastomernanoparticle composites that form a unique nanostructure during drying of the liquid coating. During drying, the nanoparticles in these liquid coatings migrate towards the substrate. The final, 100-nm-thick antireflective coatings are novel and exhibit a unique bilayer structure in which the nanoparticles are ordered and segregated towards the substrate. The coatings are rapidly cured using a new process and exhibit surprising ''scratch durability'' as measured by aggressively testing with steel wool. Sol gel chemistry is used which involves the reaction of the nanoparticles with an acrylic oxysilane to form nanoparticles which are functionalized with sol gel derived oligomers. The functionalized nanoparticles are combined with a fluoroelastomer containing a free radical initiator and multiolefinic crosslinker, and the composite film is rapidly cured by a thermal or UV process at low temperatures. The final product is a mechanically robust, low refractive index anti-reflective film which is useful for displays and photovoltaic devices. These are unique fluoropolymer nanocomposites which utilize nanoparticle self-assembly to enhance important properties.
Hydrophobic Antireflective Silica Coatings via Sol-gel Process
2008
The optical properties and structure of hydrophobic antireflective coatings (AR) deposited from silica sol and HMDS and MTMS were characterized in detail in this study. The influence of sol modification parameters on the antireflective behaviour of coatings has been investigated. For the characterization of hydrophobic coatings the water contact angle measurements, UV-visible spectroscopy and atomic force microscopy were used. HMDS modified silica coating show the highest contact angle (165°) due to its better hydrophobic covering. It was determined that the hydrophobic HMDS modified coatings reduced reflectance as well as unmodified silica AR coatings. The Nd:YAG laser damage threshold of AR modified silica coating exceeded 35 J/cm 2 at 1064 nm.
Study on low-refractive-index sol-gel SiO2 antireflective coatings
Chinese Optics Letters, 2016
A study on low-refractive-index SiO 2 antireflective (AR) coatings by a sol-gel method is reported. Variations in the properties of the coatings are related to the molar ratios of ammonia to deionized water being changed in the process of preparing the sols. From the performance test results, the optimal ratio of the reactants necessary to prepare low-refractive-index SiO 2 AR coatings is determined. Of all the SiO 2 AR coatings, the lowest recorded refractive index is 1.16 at a wavelength of 700 nm. The largest water contact angle is 121.2°, and the peak transmittance is 99.95% at a wavelength of 908 nm. Furthermore, the sol used to deposit the film with the lowest refractive index is stable because of the narrow size distribution of its constituent particles.