Study On The Preparation And Optical Property Of Polysiloxane Film With Designed Crosslinking Structure

Laser transmission efficiency is an important factor that limits the power of inertial confinement fusion（ICF）drivers.The Fresnel reflection caused by the refractive index mutation between the vacuum and core optical element seriously weakens the energy transfer during the transmission process in ICF equipment.An effective way to solve the problem is manufacturing an antireflection film on the surface of optical component.Potassium deuterium phosphate（DKDP）crystal is the core component of high power laser device.In order to obtain the high antireflection ability of laser with wavelengths of1053 nm and 527 nm,DKDP crystal needs to construct a double-layer antireflection film system on the laser incident surface.The refractive index of antireflection film prepared by conventional methods is higher（around 1.5）than the design value（around 1.36）of high refractive index film in the double-layer antireflection film system.Besides,the conventional high-temperature curing（140℃）method will cause the phase transition of the DKDP crystal（140℃）,which makes DKDP lose the frequency doubling characteristics.Therefore,It is urgent to develop a new anti-reflection film that can be cured at room temperature and has a controllable refractive index.In this thesis,methacryloxypropyltrimethoxysilane（MPS）was used as the matrix.Then the hydrolysis products with different degrees of hydrolysis were prepared by adjusting the process parameters.After that,the polysiloxane films with different crosslinking structures were obtained.At last,the dual-wavelength antireflection film system with good mechanical properties was successfully realized.The main contents and conclusions of this thesis are as follows.（1）The effects of changing hydrolysis conditions on the hydrolysis products were studied in the catalytic hydrolysis of hydrochloric acid and acetic acid,respectively.When hydrochloric acid was used as catalyst,silanol was completely condensed after hydrolysis.The hydrolysis of MPS catalyzed by acetic acid can obtain silanol monomers.As an inhibitor,THF can form hydrogen bonds with Si-OH and effectively inhibit the spontaneous polycondensation of silanols.By changing the content of THF in the water excess system,the hydrolysis products with different silanol monomer ratio were obtained.In addition,the decrease of ambient temperature during hydrolysis can partially inhibit the spontaneous condensation of Si-OH and the hydrolysis of MPS.（2）The molecular sieve was used to remove the water in the hydrolysate system that was not involved in the hydrolysis reaction.After water removal,the hydrolysate was placed in the fume hood to remove THF through airflow.The prepolymers were obtained by heating the hydrolysates after different treatment conditions.The results showes that Si-OH rapidly self-condensed without the protection of THF.Heating can promote the spontaneous polycondensation between Si-OH.The longer heating time makes the average molecular weight of the prepolymer get larger.Meanwhile,the crosslinking structures of prepolymers prepared by siloxanes with different degrees of hydrolysis are also different.It should be noted that,the increase of the hydrolysis degree of MPS will not lead to the increase of the crosslinking degree of the prepolymer.The content of water and polymerization inhibitor in the hydrolysate is the decisive factor affecting the crosslinking structure of the prepolymer.（3）Sols were prepared by mixing prepolymers with different crosslinking structures,solvents and photoinitiator.After that,the sols were coated on a silicon wafer and cured bu UV irradiation to prepare a polysiloxane film.The refractive index order of films with different crosslinking structure from low to high is three-dimensional structure,network structure,chain structure.After the addition of nano-Si O₂ particles,the refractive index of the polysiloxane film reduced to 1.3667.Meanwhile,the laser damage threshold is56.36 J/cm².After adjusting the thickness of the two layers film,the transmittance of the composite film system to the dual-wavelength laser reached 98.45%and 98.13%,respectively.