Film formation behavior and mechanical properties of one-component waterborne crosslinkable polysiloxane/fumed silica nanocomposite coatings

Abstract

One-component waterborne crosslinkable polysiloxane/fumed silica nanocomposite coatings were fabricated by mixing of vinyl dimethicone emulsion, hydrogen dimethicone emulsion, Karstedt catalyst capsules dispersion, and fumed silica dispersion. Effects of the type and content of fumed silica, catalyst dosage, and surfactant concentration on the film-formation and mechanical properties of the coatings were investigated. The hydrophilic fumed silica, Aerosil A380, with the largest specific surface area, endowed the coatings with the highest optical transparency (>80 %) and the best mechanical properties (e.g. elastic modulus: 0.95 MPa, tensile strength: 1.44 MPa, and elongation-at-break: 423 %). As the A380 content increased, the coatings exhibited descending and then ascending tack-free time, despite of catalyst dosage and surfactant concentration. The crosslinking density of polysiloxane matrix was less impacted by fumed silica if appropriate catalyst dosage was used. The fumed silica could hinder the coalescence of dimethicone droplets, hence, resulting in smooth, granular, and even porous surface of the cured films with increasing silica content. The mechanically reinforcing role of hydrophilic fumed silica for this waterborne coating was demonstrated. More surfactants and appropriate catalyst dosage favored for better mechanically reinforcing role. In addition, the nanocomposite films were breathable and thermally stable. They could potentially act as novel film-forming cosmetics, base materials carrying medicine for skin disease, and eco-friendly industrial coatings.