Preparation And Research Of Hydrophobic And Broadband SiO₂ Antireflective Film

Antireflective silica film with low cost,controllable refractive index,high laser damage threshold and so on has attractive application prospect in the anti-reflection field of the optical element surface.Whereby,sol-gel dip-coating process is the most common way to prepare this kind of film.The traditional base-catalyzed silica film have good transmission in the visible wavelengths?380-760nm?,but high reflectivity in infrared region.In this experiment,Two-layer hydrophobic and broadband antireflective film is preparaed on the glass surface from slides substrate by dipcoating process,and the two layers are researched respectively.The film/powder are charecterized and researched by SEM?TEM?UV-VIS-IR?FTIR?BET?CA and ellipsometer.It can draw the following conclusions from this experiment:1.The hydrophobic silica sol is preparaed using ammonia as catalyst,TEOS and DDS as blended precursor,HMDS as modifying agent.The effect of R(V_DDS/V_TEOS)on the sol viscosity and the effect of R or the amount of HMDS on the contact angle of film are investigated.The result shows that when R=0.31,3ml HMDS is added,the sol prepared has proper viscosity.The contact angle of film is 149°,and it can still maintain high hydrophobicity when placed in this enviroment?the temperature is25°,humidity is 90%?for two months.The film is porous structure,the refractive index is about 1.12.Due to the low refractive index,The hydrophobic film is not suitable for use alone.2.The silica sol is prepared under alkaline or acidic condition,TEOS as precursor.The variation law of the changes of sol viscosity according to the time is investigated,and the surface morphology?transmittance?abrasion resistance of film are researched.The result shows that no matter how the sol is prepared under any condition,sol viscosity remains the same in the 12d aging time.The transmittance of film under alkali catalytic condition is better than that is prepared under acid catalytic condition,but abrasion resistance is just the opposite.The reason is that base-catalysed film is formed by nano silica spherical particles,and acid-catalysed film is formed by linear polymer.3.The commixed silica sol is prepared by base-catalysed sol and acid-catalysed sol.The variation trend of the viscosity of commixed sol in the 30d is investigated,and morphology?transmittance?mechanical property?refractive index of film are researched.The results show that the viscosity of sol remains unchanged in the 30d,it is about 1mpa·s,with the increase of volume fraction of acid-catalysed sol,the mechanical property of film presents a trend of increase.When the volume fraction exceeds 10%,the refractive index of film increases first and then remains at a certain level.When the volume fraction is 30%,refractive index of film is 1.33,the pencil hardness of film is 2B,adhesion is 4.4.The hydrophobic film with low refractive index is surface layer,base/acid catalyzed film is bottom layer.Double gradient-index antireflective film is prepared by one-step or two-step method.The result shows that the transmittance of film prepared by one-step method is similar to that is prepared by two-step method.The contace angle of this film is141°,film thickness is about 200nm,There is no obvious interface between the two layers.The transmittance of the two-layer film in the rang of 380-1100nm and 1100-2500nm were increased by 7.68%and 4.39%comparing with glass substrate.