Sol-Gel Processing by Aging and Pore Creator Addition for Porous Silica Antireflective Coatings

An antireflective film produced by incorporation of polyethylene glycol (PEG) in the sol is compared to one produced using an “aged sol”. Incorporation of organic polymer in the precursor solution is a more effective method of increasing the porosity of films and transmittance of the glass substrate. Combination of aging and PEG addition increases the potential for the creation of uniformly porous structures. Aging at high oxide concentration enhances condensation and forms large silica particles containing continuous isolated silanol sites which favor PEG adsorption via hydrogen bonding. Film morphology is affected by phase separation in both the sol and during drying of film. Coating uniformity was improved by minimising phase separation during drying. This was achieved by increasing PEG adsorption by silica sol. Using this technique, coated glass with maximum transmittance of 99.7% can be produced by a simple single step coating.