Effect of Adsorbed Surfactants on the Rheology of Colloidal Zirconia Suspensions

The effect of cationic and anionic surfactant additives on the shear yield stress (τ y ) and electrokinetic behavior of concentrated zirconia (ZrO 2 ) suspensions has been investigated. The two pairs of surfactants studied were dodecylamine hydrochloride (DAC) and dodecyltrimethylammonium chloride (DTAC) and sodium dodecyl sulfate (SDS) and sodium dodecylbenzyl sulfate (SDBS). Each of the pairs differs only in the chemical structure of its headgroup. Adding each of the surfactants to concentrated zirconia suspensions increased the maximum yield stress for pH 3−11; however, within each pair, the magnitude of the increase varied substantially. The effect of added surfactant on zirconia electrokinetic behavior was not nearly as sensitive to headgroup chemical structure. Adsorption isotherms indicated that surfactant was present on the surface at very low coverage. Since the size of surfactant surface aggregates is known to be linked to headgroup chemical composition, the observed rheology could be related to such aggregate structures. In addition to demonstrating the sensitivity of concentrated suspension rheology to the exact chemical details of surfactant additives, these results suggest new interpretations of the role surfactant adsorption plays in determining the rheology of these mixtures.