EFFECT OF ZWITTERIONIC SURFACTANTS ON INTERPARTICLE FORCES, RHEOLOGY,AND PARTICLE PACKING OF SILICON-NITRIDE SLURRIES

Phosphocholine (PC) zwitterionic surfactants, with different hydrocarb on chain lengths (C6C6PC to C9C9PC), were absorbed on the surface of s ilicon nitride near the isoelectric point (pH 6), Adsorption of the su rfactants changed the lateral and normal surface forces, the rheology, and the consolidation behavior of the particles, The normal force bet ween two silicon nitride surfaces as a function of separation and the lateral (friction) forces were measured using an atomic force microsco pe (AFM), These measurements indicated that surfactant adsorption redu ced the magnitude of the long-range attractive van der Waals force and produced a repulsive short-range force, Although the adsorbed layers provided a barrier to particle contact, they could be ejected with a c ritical force that increased with the hydrocarbon chain length, The ef fect of an adsorbed layer on the viscosity and consolidation of slurri es was also measured, The viscosity of all slurries decreased with inc reasing shear rate, indicative of attractive particle networks, The hi ghest viscosity was observed for slurries formulated at the isoelectri c point without added surfactant, Much lower viscosities were observed when the surfactant concentration was greater than the critical micel le concentration (cmc), A relative density of 0.46 was obtained via pr essure filtration at 4 MPa without a surfactant, and between 0.46 to 0 .59 (C6C6PC to C9C9PC, respectively) for surfactant concentrations gre ater than the cmc, Comparing force measurements with rheology and pack ing density provides a basis for discussing the role of interparticle forces in ceramic powder processing via colloidal routes.