Effect of zwitterionic surfactants on interparticle forces, rheology, and particle packing of silicon nitride slurries

Phosphocholine (PC) zwitterionic surfactants, with different hydrocarbon chain lengths (C6C6PC to C9C9PC), were absorbed on the surface of silicon nitride near the isoelectric point (pH 6), Adsorption of the surfactants changed the lateral and normal surface forces, the rheology, and the consolidation behavior of the particles, The normal force between two silicon nitride surfaces as a function of separation and the lateral (friction) forces were measured using an atomic force microscope (AFM), These measurements indicated that surfactant adsorption reduced 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 critical force that increased with the hydrocarbon chain length, The effect of an adsorbed layer on the viscosity and consolidation of slurries was also measured, The viscosity of all slurries decreased with increasing shear rate, indicative of attractive particle networks, The highest viscosity was observed for slurries formulated at the isoelectric point without added surfactant, Much lower viscosities were observed when the surfactant concentration was greater than the critical micelle concentration (cmc), A relative density of 0.46 was obtained via pressure filtration at 4 MPa without a surfactant, and between 0.46 to 0.59 (C6C6PC to C9C9PC, respectively) for surfactant concentrations greater than the cmc, Comparing force measurements with rheology and packing density provides a basis for discussing the role of interparticle forces in ceramic powder processing via colloidal routes.