Preparation of Transparent and Antireflective Silica Thin Coatings on Plastic Substrates by Sol-Gel Process ^†

Due to their range of applications, from anti-icing to self-cleaning, low-adhesion, antibacterial, anti-reflection, anti-contamination and anti-fogging, multifunctional silica thin films are becoming very attractive in recent years [1]. Their application is widespread, including lenses for glasses, photovoltaic solar panels and mobile phones [2]. The objective of this work was to synthetized the sol-gel modified silica materials using silane precursors with various functional groups, and depositing them onto plastic substrates in order to realize transparent and antireflective coatings.

Different alkoxysilanes (tetraethoxysilane (TEOS), dimethylethoxyvinylsilane (DMVES), octyltriethoxysilane (OTES), hexadecyltrimethoxysilane (HDTMES)) were used as silica source and as modifier agents. Hybrid silica systems were synthetized by the acid-catalyzed sol-gel process at room temperature. The resulted films were dried at a temperature of 25 °C and irradiated by UV lamp (365 nm) for 10 min. The final samples were characterized both as powders (obtained after solvent evaporation) and as films deposited on plastic. The physico-chemical and structural properties of prepared sol-gel silica materials were characterized by FT-IR and UV-VIS spectroscopy, contact angle measurements and TGA analysis.

The functional groups present in the silica hybrid films were identified by FT-IR spectroscopy. Resulted coatings showed a reduction in the reflectance compared with un-coated plastic substrate (Figure 1). The reflectance of thin films was about 10% at 550 nm. In order to establish the wettability of the coatings, the sol-gel silica hybrid films were subjected to water contact angle analysis. Thermogravimetric analysis was used to test the thermal stability of the sol-gel silica hybrid materials produced from the sol-gel phase. Transparent and antireflective silica thin films were prepared by acid-catalyzed sol-gel process, using silane precursors with different functional groups (vinyl, octyl, hexadecyl) and these obtained materials can generate coatings with potential use in various fields.