The effect of surfactant adsorption on sedimentation behaviors of Al2O3–toluene suspensions

The sedimentation behavior and suspension stability of submicrometer Al2O3 powder–toluene mixtures have been investigated using various organic surfactants to aid powder dispersion in a dilute solids concentration (4.8 vol.%). The surfactants used include a commercially-available, carbonate-based dispersant (hereafter termed the ‘SOL’) and some fatty acids (e.g. stearic acid ‘SA’, oleic acid ‘OA’ and 12-hydroxystearic acid ‘HSA’) in a concentration range 0.3–5 wt.% of the alumina loading. The experiment reveals that the surfactant nature is critical to the suspension stability. The suspensions follow a decreasing order of stability SOL>HSA>SA>OA for the Al2O3–toluene mixtures. This surfactant-dependent behavior is critically related to the adsorption affinity of the surfactant molecules on the powder surface in the carrier medium. The adsorption isotherms exhibit the Langmuir-typed behavior and reach a saturation plateau over a range of 1.3–2.4 mg m−2, revealing a surfactant-specific characteristic.