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

Abstract

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°.