Views:6 Author:Site Editor Publish Time: 2019-09-24 Origin:Site
Dispersants are widely used to improve dispersion stability. According to the DLVO (Derjaguin, Landau, Vervey, and Overbeek) theory, particles in aqueous media can be agglomerated when van der Waals attraction is greater than electrostatic repulsion (Verwey et al., 1999; Derjaguin and Landau, 1941). By adding suitable dispersants, steric hindrance and electrostatic stabilization between the abrasives are obtained, which prevent abrasives from agglomerating.
Generally, abrasive particles in slurry are known to undergo transitions from bridging agglomeration → stable → depletion flocculation with an increase in dispersant concentration (Kim et al., 2012). At a low concentration, dispersants are insufficient for full coverage of the abrasive surface. The free segments (loops and tails) of the adsorbed dispersant on the abrasive surface can attach to other abrasives, leading to bridging agglomeration. When an adequate amount of dispersant is added, it fully covers the abrasive surface, which can improve the dispersion stability through steric hindrance and electrostatic stabilization. Also, dispersants should have strong adsorption energy with the abrasive surface. Weak adsorption energy between dispersant and abrasive surface causes desorption of the dispersant during a particle collision, resulting in bridging flocculation (Sigmund et al., 2000). At a high concentration of dispersants, free dispersants (not adsorbed) can promote flocculation of the stable slurry through a depletion mechanism (Asakura and Oosawa, 1954, 1958). When two particle surfaces approach each other at a distance less than the effective diameter of unabsorbed dispersants, the dispersants are excluded from the interparticle gap, resulting in an osmotic pressure. This osmotic pressure generates an attractive force between the abrasive particles, which promotes their flocculation. Thus, it is important to add an adequate amount of dispersants for improved dispersion stability.