CONTROLLED MODIFICATION OF SILICON-NITRIDE INTERACTIONS IN WATER VIA ZWITTERIONIC SURFACTANT ADSORPTION

The density and viscosity of a slurry of colloidal particulates are dictated by the interactions between the constituent particles in the suspension. We discuss the forces required for maximum density and minimum viscosity for a flocculated slurry, and suggest a means of obtaining this force between silicon nitride particles by adsorption of a bilayer of zwitterionic surfactant, diheptanoic-sn-glycero-3-phosphocholine, from solution. The normal (e.g. adhesion) and lateral (friction) forces between two silicon nitride surfaces in water were measured using an atomic force microscope (AFM), both in the presence and absence of this surfactant. In both cases the normal force is attractive, but the attraction is much weaker in the presence of the surfactant. A short-range repulsive force and a much weaker lateral force are measured between the coated surfaces. These are the desired interparticulate forces. Finally, we discuss the influence of lateral- and normal-surface forces on the consolidation and viscosity of particulate suspensions, and describe some in influences of lateral forces on the AFM imaging process.