Figure 3 . Transmittance spectra of a single-layer quarterwave AR coating and an experimental and modeled double-wavelength AR coating.

No abstract

Hydrophobic antireflective coatings with a low refractive index were prepared via a base/acid-catalyzed two-step sol-gel process using tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors, respectively. The base-catalyzed hydrolysis of TEOS leads to the formation of a sol with spherical silica particles in the first step. In the second step, the acid-catalyzed MTES hydrolysis and condensation occur at the surface of the initial base-catalyzed spherical silica particles, which enlarge the silica particle size from 12.9 to 35.0 nm. By a dip-coating process, this hybrid sol gives an antireflective coating with a refractive index of about 1.15. Moreover, the water contact angles of the resulted coatings increase from 22.4 to 108.7° with the increases of MTES content, which affords the coatings an excellent hydrophobicity. A "core-shell" particle growth mechanism of the hybrid sol was proposed and the relationship between the microstructure of silica sols and the properties of AR coatings was investigated.

Thick silica antireflective (AR) coatings with controlled thickness and durable AR performance were prepared by a base-catalyzed sol-gel process using tetraethyl orthosilicate (TEOS) as precursor and hydroxyl-terminated polydimethylsiloxane (PDMS) as a modifier. The addition of PDMS greatly increased the controllable viscosity range of the silica sol but did not obviously affect the particle size. This phenomenon is attributed to a "compulsive aggregation" process of the sol, which involves the formation of "PDMS bridges" between silica particles in the sol. The mechanism of "PDMS bridge" formation is proposed based on sol viscosity, sol particle size changes, and FTIR identification. The increased controllable viscosity range provided a convenient way to prepare AR coatings with controlled thickness and therefore with controlled wavelength of maximum transmittance. The introduction of PDMS into the silica sol also increased the hydrophobicity and hence the durability of the AR coatings in wet environments.