The effect of cationic and anionic surfactant additives on the shear yield
stress (tau(y)) and electrokinetic behavior of concentrated zirconia (ZrO2)
suspensions has been investigated. The two pairs of surfactants studied we
re dodecylamine hydrochloride (DAC) and dodecyltrimethylammonium chloride (
DTAC) and sodium dodecyl sulfate (SDS) and sodium dodecylbenzyl sulfate (SD
BS). Each of the pairs differs only in the chemical structure of its headgr
oup. Adding each of the surfactants to concentrated zirconia suspensions in
creased the maximum yield stress for pH 3 - 11; however, within each pair,
the magnitude of the increase varied substantially. The effect of added sur
factant on zirconia electrokinetic behavior was not nearly as sensitive to
headgroup chemical structure. Adsorption isotherms indicated that surfactan
t was present on the surface at very low coverage. Since the size of surfac
tant surface aggregates is known to be linked to headgroup chemical composi
tion, the observed rheology could be related to such aggregate structures.
In addition to demonstrating the sensitivity of concentrated suspension rhe
ology to the exact chemical details of surfactant additives, these results
suggest new interpretations of the role surfactant adsorption plays in dete
rmining the rheology of these mixtures.