Induced flocculation in sterically stabilized ceramic powder dispersions

Abstract

Stabilization of dispersions of silicon in benzene and trichloroethylene by adsorption of polystyrene [PS], poly (methyl methacrylate) [PMMA] and co-poly (styrene, methyl methacrylate) [co-PS-PMMA] was investigated. Isotherms for the adsorption of these polymers onto silicon were measured. Dispersions of silicon with adsorbed PMMA or co-PS-PMMA were found to be effectively stabilized. The degree of steric stabilization was found to depend on the polymer-medium interactions, the chemical structure of the polymers and the surface chemistry of the silicon powder. Flocculation was induced in the stabilized suspensions by the addition of n-hexane as a non-solvent. The amount of n-hexane needed to achieve theta conditions in the solvent was determined by carrying out cloud point titrations. This was compared to the critical volume of n-hexane needed to induce flocculation in the sterically stabilized silicon dispersions. The effects of polymer—medium interactions and temperature on these phenomena were observed. The present study is of direct relevance to the processing of ceramic powder dispersions used in the manufacture of ceramic monoliths and composites.