SiO2 Nanoparticles Modified by Bridged Polysilsesquioxane-Based Protective Coatings for Moisture Proofing and Antireflection Applications

A multifunctional protective coating with satisfactory moisture-proof and antireflective (AR) performance has been successfully fabricated by modifying SiO2 nanoparticles with an acid-catalyzed hexylamine and 3-glycidoxypropyltrimethoxysilane bridged polysilsesquioxane (HG-BPSQ). The preparation process is simple and environmental-friendly with no need for any post-treatments. Instead of destroying the nanoporous structure of the SiO2 coating, the introduced HG-BPSQ can improve the moisture-proof and enhance the mechanical property of the porous SiO2 coating. Experimental results show that the refractive index of the corresponding coating packed by the hybrid nanoparticles is as low as 1.22, and the average transmittance of the quartz coated with hybrid coating is 97.21% in the range of 300–1200 nm, which is far greater than that of the bare quartz's 91.98%, indicating the hybrid possesses good AR performance. In addition, the average transmittance of the potassium dihydrogen phosphate (KDP) crystal coated with the hybrid coating only decreases 2.54% after being treated in a 60% humidity environment for 7 months, which is far lower than that of the bare KDP and KDP coated with SiO2 coating, illustrating the hybrid coating has good moisture-proof performance. What's more, the abrasion-resistance ability of the hybrid coating is better than that of the SiO2 coating. Based on the experiment results, the formation mechanism of moisture-proof and AR function of the hybrid coating has been deduced and simulated. This work provides a simple and environmentally friendly way by using BPSQ to improve the moisture-proof and mechanical performance of the SiO2 coating while maintaining its antireflective property.