Dispersion stability evaluated by experimental design

The stability of paraffin and hydrocarbon oil dispersions stabilized by non ionic surfactants has been systematically evaluated. Using experimental des ign, the influence of the following parameters on dispersion stability was studied: surfactant concentration, shear rate, shear time and temperature o f homogenisation. The experiments were evaluated with respect to particle s ize and particle migration velocity by a scanning optical analysis techniqu e. This scanning technique monitors physical variations in a dispersion as a function of time and the technique is well suited for evaluation of dispe rsion stability. It was found that the only factor examined affecting parti cle migration velocity in a significant way was the surfactant concentratio n. A pronounced maximum in a reaming rate was obtained at around 10 wt% sur factant both for the paraffin dispersions (suspensions at room temperature) and for the hydrocarbon oil emulsions. This surfactant-induced instability is explained as depletion flocculation caused by elongated surfactant mice lles or by small oil-containing aggregates formed as microemulsion droplets during the emulsification process.