Structural Control And Properties Of Multifunctional Coatings

In the high-power laser system,the loss of laser energy caused by the Fresnel reflection on the surface of the optical elements needs to be reduced.Different types of optical elements have different requirements for the coatings,including the need for high transmittance of single wavelength or multi-wavelength,and broadband anti reflection.The sol-gel method has many advantages in the preparation of the antireflective coating,such as low cost,high chemical purity,high preparation efficiency and strong ability to resist laser damage.However,the antireflective coatings prepared by sol-gel method also have their own shortcomings.Due to the high porosity and surface molecular group polarity,the gas pollutants in the environment are easily adsorbed,and thus the optical transmission properties of the components are reduced and the laser energy transmission is affected.How to improve the anti-pollution ability of silica coatings is a great challenge.According to our analysis of the physical and chemical properties of the coatings,the control of the structure and the functionalization of the surface molecular groups are the most promising solutions.It is difficult for the single-layer antireflective coating to meet the requirement of broadband antireflection or multi-wavelength antireflection.According to the theory of antireflection,the preparation of refractive index gradient coatings is the most suitable method to realize this goal and the combination of different refractive index layers is also a good method.All these have put forward an urgent need for the regulation of the refractive index of the coating.Based on the above requirements,this paper studies the synthesis of silica nanoparticles,the structure regulations and surface functionalization of colloid particles,the regulations of the structure and their performances.We have tried to prepare silica coatings with self-cleaning effect to improve the anti-pollution ability.The preparation of ultralow-refractive-index coatings may serve for broadband or multi-wavelength antireflection.The follow-up chapters in this paper are the main research works and achievements.(1)We prepared ultralow-refractive-index antireflection silica coatings by the construction of hollow silica nanoparticles and surface modification,studying the refractive index of the coating and other important properties systematically,and put forward a reasonable model to explain the relationship between the microstructure of silica nanoparticles and the refractive index of the coatings.The refractive index of coatings can be easily adjusted in the range of 1.17-1.08 due to the abundant pores and porosity of hollow spheres.It is easy to control the refractive index of the coating,which may contribute greatly for the fabrication of refractive index gradient or multi-wavelength antireflective coating.(2)By synthetizing the hollow silica nanoparticles and changing the order of adding the precursor,a low refractive index multifunctional antireflective coating with self-cleaning properties was prepared.The possible growth mechanism of the new silica particles was clarified,and the effects of the double scale roughness and the low surface energy groups on the superhydrophobic properties were revealed.The coatings not only showed excellent superhydrophobic performance,excellent mechanical flexibility,good chemical and mechanical stability,but also achieved ultralow refractive index(as low as 1.07).Superhydrophobicity was achieved on the substrates of K9 glass,PVC,Ginkgo leaves,LY12 aluminum alloy and stainless steel,and the water contact angle on the stainless steel reached 166°.The thermal stability test showed that the coatings can keep their superhydrophobicity under 350?.After calcination at 500?,the coating had antifogging performance.More than 100 cycles of bending test indicated that the coating has good mechanical flexibility and the hydrochloric acid immersion test showed that it could resist the corrosion of strong acid solution with pH value of 1.(3)With the aid of film-designing software,a robust and high performance broadband antireflective coating has been designed and successfully prepared.The coating combined the advantages of coatings prepared from both the acid-catalyzed sol and the base-catalyzed sol,achieving high quality of broadband antireflection in the visible light range and good mechanical properties.After 24h HMDS treatment,the water contact angle reached 126? and had excellent environmental stability.The bottom layer of the double-layer system has a refractive index of 1.39 and a thickness of 104 nm,and the refractive index of the top layer is 1.17 and the thickness is 115 nm.In the range of 400-800 nm,the highest transmittance is 99.87%(591 nm),and the average transmittance achieves 99.40%.In addition,the three-dimensional network structure affords the coatings a good mechanical flexibility and scratch resistance.The pencil hardness reached 3H,and passed the tape sticking test.