Comparative study on hydrophobic anti-reflective films from three kinds of methyl-modified silica sols

Methyl-modified silica sols were prepared with the polymer of methyltriethoxysilane (MTES), the polymer of dimethyldiethoxysiloxane (DDS), and hexamethydisizane (HMDS) as mono-, di-, and tri-methyl modifiers respectively. By comparing the size and the shape of clusters in three different methyl-modified silica sols, the special nature of the sol was found to be the key to the property of films. Different modal modification of methyl to silica particles led to different cluster fractal structures that influenced the morphology, the porosity of films and consequently the anti-reflection characteristics. The contribution of methyls in or on clusters directly determined the hydrophobicity. Using mono- or di-methyl-modified silica sol, the film/water contact angles were less than 120°. But it could reach 165° when using tri-methyl-modified silica sol. The lowest reflectivity of film could reach 0.0% for all the three modified sols. As a result of the comparative study, tri-methyl-modified silica sol was more suitable to prepare hydrophobic anti-reflective film with required high optical performance.