Tristyrylphenol based surfactants as efficient dispersants of TiO2 particles in dilute and concentrated dispersions

Titanium dioxide (TiO₂) is widely used as a pigment in the formulation of paints. Due to the high content of TiO₂ particles in the formulations, dispersants are required to avoid their aggregation. This study presents two bulky surfactants, namely, tristyrylphenol ethoxylate (TSEO, uncharged) and tristyrylphenol ethoxylate phosphate (TSEO-P, negatively charged), for the stabilization of commercial TiO₂ particles at pH 8.0 (close to that used in the formulation of paints). X-ray photoelectron spectroscopy (XPS) revealed the presence of Ti, Al, Si, O and C on the surface of the commercial TiO₂ particles. Batch adsorption experiments performed in the dilute range (1.0 wt%) indicated that the negatively charged TSEO-P adsorbed more efficiently on TiO₂ particles (338 mg/g) than the TSEO surfactant did (qₑ = 222 mg/g), increasing the ζ-potential of TiO₂ particles from – 24.4 ± 1.0 mV to – 39.1 ± 1.6 mV. Hydrophobic interaction between the hydrophobic tristyryl group and the organic molecules on the surface of the TiO₂ particles favored the exposition of the phosphate groups to the medium. H bond between phosphate (HPO₃⁻) and hydroxyl groups on the surface exposed the tristyryl groups to the aqueous medium, which could interact with other surfactant molecules by π-π interactions. Such structuring of surfactant (at 2.0 wt%) molecules on the TiO₂ particles provided colloidal stability for TiO₂ particles in the slurries (70 wt%) over 30 days at 25 °C and 52 °C, which was comparable to that provided by sodium polyacrylate (PAS, at 1.0 or 2.0 wt%). The flat paint film formulated with TSEO-P (2.0 wt%) presented a contact angle of 58.5 ± 1.0°, and superior wet scrub and leaching resistance in comparison to those prepared with sodium polyacrylate (2.0 wt%), which presented a contact angle of 52.8 ± 0.8°.