A molecular investigation of adsorption onto mineral pigments.

摘要

Pigment suspensions are important in several processes such as ceramics, paints, inks, and coatings. In the wet state, pigments are combined with a variety of chemical species such as polymers, surfactants, and polyelectrolytes which produce a complex colloidal system. The adsorption, desorption, and redistribution of these species at the pigment-aqueous solution interface can have an impact on the behavior in both the wet state or its final dried state. The goal of this work is to establish a molecular picture of the adsorption properties of these pigmented systems.; A novel in situ infrared technique has been developed which allows the detection of adsorbed surface species on pigment particles in an aqueous environment. The technique involves the use of a polymeric binder to anchor the colloidal pigment particles to the surface of an internal reflection element (IRE). The binder only weakly perturbs about 25% of the reactive surface sites (hydroxyl groups) on silica. The reaction of succinic anhydride with an aminosilanized silica surface has been quantified using this technique.; The adsorption dynamics of the cationic surfactant cetyltrimethylammonium bromide (C₁₆TAB) at the TiO₂-aqueous solution interface has been investigated using Fourier transform infrared-attenuated total reflection spectroscopy (FTIR-ATR) and electrokinetic analysis. At low bulk concentrations, C₁₆TAB is shown to adsorb as isolated islands with a “defective” bilayer structure. Anionic probe molecules are shown to effectively “tune” the adsorbed surfactant microstructure. The results indicate that the structure of the adsorbed surfactant layer, and not the amount of adsorbed surfactant, dictates the subsequent adsorption behavior of the system.; Atomic Layer Deposition is used to deposit a TiO₂ layer onto the surfaces of silica and kaolin pigments. The process involves the cyclic reaction sequence of the vapors of TiCl₄ and H₂O. Three complete deposition cycles are needed before the surfaces of the modified pigments are dominated by the presence of TiO₂. The modified kaolin pigments display increased dispersion stability as compared to the parent kaolin. The electrokinetic behavior of the modified kaolin is shown to be identical to that of pure TiO₂ pigments.