A double-layer moisture barrier & antireflective film based on bridged polysilsesquioxane and porous silica

A double-layer film with both moisture barrier protective and antireflective (AR) abilities was prepared. The upper layer was a porous silica AR film. The bottom layer was a nonporous bridged polysilsesquioxane (BPSQ) moisture barrier protective film based on the sol-gel process of a newly synthesized X-bridged silsesquioxane (EG-BPSQ) monomer. The EG-BPSQ monomer was synthesized via the stoichiometric reaction between 3-glycidoxypropyltrimethoxysilane (GPTMS) and ethylene diamine (EDA) at 60 °C with no catalyst. The high polycondensation of the inorganic matrix and the special X-bridging organic chain in EG-BPSQ resulted in the dense structure of the protective film. Transmittance of a KH₂PO₄ (KDP) crystal coated with the EG-BPSQ film only decreased 1.11% at a wavelength of 1053 nm and 1.49% at a wavelength of 351 nm when tested after being in a 60% humidity environment for 100 days, indicating that the EG-BPSQ protective film possessed an excellent moisture barrier performance for the KDP crystal. For the double-layer film coated on KDP crystal, good AR performance was obtained: 98.09% at a wavelength of 1053 nm and 99.51% at a wavelength of 351 nm.