Preparation Of Silica Anti-Reflective Coating And Study On Its Surface Properties

In the optical instrument, the optical element surface is coated with antireflective coatings to reduce reflection of light on the surface of the optical element and increase the transmittance of light. Thereby, the coatings can improve the element’s performance in the operating wavelength or band. This thesis is about preparation of 3 kinds of AR coatings using dip coating method based on the sol-gel prepared SiO2 sol. The coatings’ transmittance, surface morphology and environmental resistance have been researched.In this paper, we demonstrated a method of fabricating broadband antireflection coatings based on the layer-by-layer self assembly of the positively charged layer double hydroxides (LDH) nanosheets and the negatively charged silica nanoparticles via electrostatic interaction. Firstly, SiO2 sol with different sizes was prepared. And the influence of the amount of ammonia on the average particle size was investigated. The results showed that particle size and particle size distribution increased while increasing the amount of ammonia. The influence of the average particle size and the dipping time on the transmittance of the single-layer AR coatings was investigated. For LDH/SiO2 composite AR films, LDH concentration, the average particle size and numbers of bilayers were also investigated. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to observe the morphology and structure of the LDH/SiO2 multilayer coatings and their surface topography.We prepared a kind of silica AR coating with similar hollow structure. We demonstrated an orthogonal method to study the influence of the preparation method of zinc oxide nucleation layer and silica shell on the performance of the prepared AR coatings. And the optimum reaction conditions were achieved. The AR coating fabricated by impregnating zinc oxide as its nuclear layer obtained the maximum transmittance of 95.5% while using an average particle size of 50 nm silica nanoparticles as its shell with 3 times of the 15 min immersion time each. The AR coating fabricated by the decomposition of zinc acetate as its nuclear layer obtained the maximum transmittance of 98% when the concentration of zinc acetate was 10 mM with 3 h of growth time and the average particle size of sol-gel prepared silica nanoparticles was 80 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the morphology and structure of the silica AR coatings.We demonstrated the dip-coated method to fabricate a kind of hydrophobic AR coating using doped silica sol. The influence of molar ratio of CPTES and TEOS and the bilayer number of PDDA and silica nanoparticles with the average particle size of 25 nm was investigated on the transmittance and hydrophobicity of the AR coatings. The results showed that, the coatings could simultaneously obtain the better antireflection effect and hydrophobicity when the molar ratio of CPTES and TEOS is 1.0. Moreover, the AR coating could obtain the maximum transmittance of 99% with a 89.5° water contact angle while fabricating four PDDA/SiO2 bilayers.We selected several series of AR coatings to study their environmental resistance, such as, silica AR coatings prepared by an average particle size of 50 nm silica nanoparticles, LDH / SiO2 multilayer coatings of [LDH (0.4 g/L)/SiO2 (25 nm)]6 and [LDH (0.8 g/L)/SiO2(25 nm)]6, and hydrophobic modified AR coating C4. We compared the transmission changes of the four AR coatings within 30 days, as well as the transmission changes after washing. The results showed that the composite AR coatings and the hydrophobic modified AR coatings had less reduction in transmittance within 30 days than silica AR coatings. Therefore, they were more stable and had better environmental resistance.