D. Liu et Sg. Malghan, ROLE OF POLYACRYLATE IN MODIFYING INTERFACIAL PROPERTIES AND STABILITY OF SILICON-NITRIDE PARTICLES IN AQUEOUS SUSPENSIONS, Colloids and surfaces. A, Physicochemical and engineering aspects, 110(1), 1996, pp. 37-45
The role of ammonium polyacrylate in modifying the interfacial propert
ies of silicon nitride powder was examined systematically in order to
understand the basic mechanism of dispersion. The adsorption of the po
lyacrylate on silicon nitride powder was found to be dependent on both
the pH and its residual (equilibrium) concentration. The interfacial
charge properties of the silicon nitride powder can be modified to a l
arge extent by the adsorbed polyacrylate and equilibrium pH. Well-disp
ersed silicon nitride suspensions can be obtained in both the neutral
and alkaline pH range by the application of ammonium polyacrylate. The
enhanced electrostatic repulsion between the dispersant-modified powd
er surfaces was found to be the primary mechanism governing the disper
sion. Also, the steric interactions of the adsorbed polyacrylate with
aqueous media were demonstrated in this work to have a positive contri
bution to the dispersion. The latter is attributed to the hydrophilic
nature of the polyacrylate. The dispersing functions of the adsorbed p
olyacrylate were understood to arise from the two oxygen atoms in the
carboxylic group of the polyacrylate. The charged oxygen atom in the c
arboxylic group was responsible for the measured interfacial charge pr
operties of the dispersant-modified powder. The uncharged oxygen atom
had an additional contribution to the hydrophilic nature of the adsorb
ed dispersant layer.