Influences of monomer and oligomer structures on their adsorption on metal oxide surfaces

The adsorption from alkaline solutions of a series of monomeric organic acids on metal oxide treated TiO2 aqueous dispersions is examined. Substituents containing a combination of carboxylic acid and hydroxyl groups were observed to adsorb significantly, whereas those containing only acid or hydroxyl groups did not adsorb significantly. Based on these results, two types of oligomeric dispersants were synthesized to provide stability to aqueous TiO2 dispersions. In the first series, the adsorption sites were in the terminal positions of poly(oxyethylene) oligomers of variable lengths. Based on the monomeric acid studies, the terminal adsorption units in these “claw” stabilizers were malic acid groups. To provide greater adsorptive strength, oligomers with repeating adsorption units along the mainchain also were synthesized. Oligomers of this type included poly(aspartic acid) and maleic acid alternating co-oligomers with oxyethylene branches extending from the mainchain. The adsorption of these materials on metal oxide surface treated TiO2 and their influence on the rheology of TiO2 dispersions at a high volume fraction are discussed.