Tetraethylorthosilicate-containing barrier dispersion coatings—Mechanism of action

Abstract

We demonstrate the use of tetraethylorthosilicate (TEOS) as a silica precursor for water barrier poly(styrene-butadiene) latex dispersion coating applications. The TEOS is adsorbed at the surface interface by the latex particles in the aqueous dispersion due to the hydrophobic nature of the surface and the TEOS. It then undergoes hydrolysis and condensation to the silica phase in the interstitial sites in the partially dry close-packed polymer structure. The fully cured film exhibits a greater degree of coalescence than films prepared from the unmodified latex binder. Large discrete silica particles are not formed within the cured film; rather the films contain homogenous silica dispersion with a probable particle size no larger than 10 nm. This higher degree of coalescence results in improvements in water vapour barrier performance from 121 – 20 g m−2 d−1, with direct water barrier performance (Cobb 120 s) improving from 25 to < 2 g m−2, compared to the silica-free film.