Silicon Nitride Colloidal Probe Measurements: Interparticle Forces and the Role of Surface‐Segment Interactions in Poly(acrylic acid) Adsorption from Aqueous Solution

Abstract

Direct measurements of forces between silicon nitride surfaces in the presence of poly(acrylic acid) (PAA) are presented. The force-distance curves were obtained at pH > pH iep with an atomic force microscopy (AFM) colloidal-probe technique using a novel spherical silicon nitride probe attached to the AFM cantilever. We found that PAA adsorbs onto the negatively charged silicon nitride surface, which results in an increased repulsive surface potential. The steric contribution to the interparticle repulsion is small and the layer conformation remains flat even at high surface potentials or high ionic strength. The general features of the stabilization of ceramic powders with PAA are discussed; we suggest that PAA adsorbs onto silicon nitride by sequential adsorption of neighboring segments ("zipping"), which results in a flat conformation. In contrast, the long-range steric force found in the ZrO 2 /PAA system at pH > pH iep arises because the stretched equilibrium bulk conformation of the highly charged polymer is preserved via the formation of strong, irreversible surface-segment bonds on adsorption.

Dispersion of TiN in aqueous media

“…Strong lateral repulsion between neighboring chains leads to a low adsorbed amount (see Fig. 3), similarly to the case for PAA on Si 3 N 4 [55]. With increased slurry pH, the extent of the nonelectrostatic effect increased and became dominant at high pH (>10.2), where PEI molecules were practicably uncharged.…”

Polyelectrolyte-mediated surface interactions

“…This indicates a high degree of dissociation of the anionic polyelectrolyte and that the polyelectrolyte chains are stretched away from the surface. In contrast, flat layers of PAA adsorbed on negatively charged Si 3 N 4 surface under condition of pHNpH iep were found by Laarz et al [51]. The pronounced differences in PAA conformation on the two negatively charged mineral surfaces were explained by differences in local surface-segment attraction.…”

DLVO Interactions of Tungsten Oxide and Cobalt Oxide Surfaces Measured with the Colloidal Probe Technique

“…Much work has been carried out on materials with relevance to slurry processing of ceramics (3)(4)(5)(6), but the only AFM surface force study including WC in water, known to the authors, is the early study by Weisenhorn et al (7) where the force was measured between a WC tip and a gold surface in water.…”