One-step sol-gel preparation of PDMS-silica ORMOSILs as environment-resistant and crack-free thick antireflective coatings

Polydimethylsiloxane (PDMS)-silica ORMOSIL (organically modified silicate) sols were prepared by a one-pot sol-gel process using tetraethyl orthosilicate as an inorganic precursor and hydroxyl-terminated PDMS as an organic modifier, and antireflective (AR) coatings were prepared with these sols by dip coating. It was found that the addition of PDMS to silica sols significantly increased the viscosity and the controllable viscosity range of the silica sols, affording us a simple route to prepare very thick AR coatings with controlled thickness by a single deposition step. The coated fused silica substrates retained very high transmission of up to 99.9% at a determined wavelength. The addition of PDMS to the silica sols improved the hydrophobicity and abrasion-resistance of the coating, and prevented to some extent the coating from cracking which occurred in a pure inorganic thick AR coating. The PDMS-silica ORMOSIL AR coatings are stable after standing for 2 months at room temperature in an environment of 95% relative humidity. The relationship between structure and properties of the coatings is discussed considering the particle growth mechanism.