Fabrication of mechanically robust antireflective films using silica nanoparticles with enhanced surface hydroxyl groups

Abstract

The outdoor application of antireflective (AR) films requires not only high transmittance but also mechanical properties such as good abrasion-resistance, and certain AR durability to resist the damage of the harsh environment. In the study, high mechanical performance was achieved by using a binder system in conjunction with the silica nanoparticles (SiO₂-NPs). Hydrogen peroxide (H₂O₂) as a hydroxyl modifier repaired the surface Si–O bonds of SiO₂-NPs effectively. The density of surface hydroxyl groups of the SiO₂-NPs modified with H₂O₂ (H₂O₂–SiO₂-NPs) was boosted from 1.08/nm² to 2.00/nm², providing an effective route to prepare very robust AR films with abundant Si–O–Si bridging chemical bonds. The addition of linear silicate polymers (SiO₂-LPs) into the silica sols performed the function of a polymer binder and markedly improved the abrasion-resistance and AR durability of the films. The H₂O₂–SiO₂-NP/LP composite films derived from these sols possessed excellent optical and mechanical properties. The average transmittance of the composite films reached 97.5% in the visible spectrum, in contrast to 92.0% for a bare glass substrate. Furthermore, the film with a hardness value of 1.7 GPa could pass a 7H pencil test. Moreover, the relationship between structure and properties of the films was discussed considering the formation mechanism.