Development of Short‐Range Repulsive Potentials by Short‐Chain Surfactants in Aqueous Slurries

Abstract : The effect of both cationic (n-trimethylammonium bromide, CnTAB) and zwitterionic (phosphocholine, CnCnPC) surfactants on the properties of aqueous slurries of silicon nitride was studied. These surfactants were expected to adsorb to the surface of silicon nitride particles to produce short-range repulsive interparticle potentials that might be useful for the colloidal processing of advanced ceramic powders. Electrophoretic, adsorption, and viscosity measurements showed that longer chain length surfactants (CnTAB, n greater than or equal 12 and CnCnPC, n greater than or equal 9) strongly adsorb. Surfactants with shorter chain lengths were highly soluble and did not adsorb. Although the CnTAB, n greater than or equal 12 surfactants produced very weak particle networks with a low viscosity, the packing density during consolidation was very low, and the bodies were brittle (cracked before plastic deformation). The less soluble, longer chained CnCnPC, n greater than or equal 9 surfactants did produce high particle packing densities, but also produced brittle bodies. In all cases, it appeared that the surfactants could be pushed away from the surface during particle packing.