Research On Thermal Curing Mechanism And Application Of Functional Coatings Of Organic Polysilazane

As a new organic and inorganic hybrid material,polysilazane has strong designability in structure and multiple curing processes.The cured coating can be combined with the substrate through the covalent bond with compact and thin properties,which leads to the broad application prospect in the functional protective coating.However,the structural changes of polysilazane curing process have not been revealed,and difficult to regulate the coating properties,which seriously restricts its application in photovoltaic panels,aerospace,biomedicine,and other high-end fields that have high requirements for material properties.To solve this problem,we systematically studied the thermal curing process and mechanism of polysilazane,and explored the application of polysilazane with different molecular structures in photovoltaic cell encapsulation film,spacecraft structure protective coating,and smart antibacterial protective coating for contact lenses.Firstly,the regulation of substituents on the polysilazane resin thermal curing mechanism was systematically studied by monitoring the chemical structure.It is found that the curing process of polysilazane is divided into main chain structure and side chain structure changes,in which the main chain changes from the secondary amine structure of Si-NH-Si to the tertiary amine structure of Si-N with a higher crosslinking degree.Si-H was hydrolyzed and condensed between different molecular chains to form a highly cross-linked network of Si-O-Si.In the side chain structure,Si-CH=CH₂ substituted polysilazane was cured by vinyl polymerization.Polysilazanes containing Si-CH=CH₂ and Si-H units are cured by vinyl polymerization and hydrolyzing condensation.If the alkoxy group is introduced into the polysilazane,the curing temperature can be reduced from 170 ^oC to below 80 ^oC by the catalytic condensation of water dehydrating alcohol.On this basis,we studied the encapsulation effect of the above three polysilazane resins on photovoltaic cell modules.The results show that the three kinds of polysilazane resins can form dense silicon oxide films with a thickness of 200-300 nm and a small amount of N element on the surface of monocrystalline silicon under the oxidation action of 800 ^oC.The coating volume shrinkage is less than 50%,the light transmission in the visible band is nearly100%,and the core performance indexes are better than traditional silicone resins.It can effectively solve the problems of the traditional packaging coating,which is easily damaged by aging and poor transmittance,showing good application potential.The coating formed by Si-CH=CH₂-replaced polysilazane resin has good high-temperature resistance and minimum volume change rate,we tried to apply it to the atomic oxygen（AO）erosion protection of spacecraft structural components in low orbit space.We selected PPS as the substrate,and found that after plasma activation for 10 min,the surface of the activated PPS and the coating can be combined by covalent bond,showing good thermal shock resistance,and can withstand 200 high-and low-temperature shock cycles of-196 ^oC to 150^oC.With the cumulative AO flux of 5.22×10²¹ atoms cm^-2,the thickness of 1.7μm coating can effectively resist the AO erosion and the mass loss is only 6.48%of that of the uncoated sample.In addition,we used the low curing temperature of triethoxylsilane-modified polysilazane to construct a coating on the surface of contact lenses with intelligent antibacterial,ultra-flat（coarse-forming degree less than 1 nm）,high transparency,UV aging resistance,and abrasion resistance.Its intelligent antibacterial activity is due to the p H change caused by bacterial infection triggering the release of NH₄⁺from the coating,and the killing rate of keratitis-related pathogens such as Escherichia coli and Staphylococcus aureus can reach 95%and97%respectively,which is expected to prevent the occurrence of keratitis without affecting the optical properties of contact lenses.