COLLOIDAL PROCESSING OF SILICON-NITRIDE WITH POLY(ACRYLIC ACID) - II - RHEOLOGICAL PROPERTIES

Poly(acrylic acid) (PAA) was the focus of an investigation in the role and behavior of polyelectrolyte dispersants in aqueous-based colloida l processing of silicon nitride, The steady-shear flow properties of d ense suspensions were examined as a function of pH, particle volume fr action, chain length, and polymer concentration. Suspensions exhibited shear-thinning behavior, which was analyzed using the constitutive Bi ngham equation for plastic flow. The data showed that polyelectrolyte charge and configuration were important in the observed flow behavior. In acidic media, PAA behaved similar to a neutral polymer in a poor s olvent, whereas, in alkaline media, PAA behaved similar to a rigid asy mmetric particle. Although electrostatic forces dominated flow propert ies in alkaline media, where PAA was predominantly in the free-polymer form, at lower pH values, PAA interactions with the particle surface resulted in a complex array of suspension effects, including polymer b ridging, electrosteric stabilization, and flocculation.