Interparticle forces arising from adsorbed surfactants in colloidal suspensions: An additional attractive force

The effects of alkyl chain length and concentration of surfactant on the yield stress-pH behavior of a 57 wt% ZrO₂ suspension were evaluated. An alkyl chain length n of between 5 to 12 carbons was used. For chain length n ≤ 7, a much larger maximum yield stress (at zero zeta potential) than that without additive was recorded. The increase in the maximum yield stress is as much as sixfold. Generally, a higher surfactant concentration leads to a higher yield stress. The increase in the maximum yield stress is quite insensitive to surfactant chain length. Ionic strength appears to have no effect on the yield stress-pH behavior of suspensions with a surfactant. The data are consistent with the observation of a long-range attractive (hydrophobic) force measured in surface force experiments.