Effect of collision on self-assembly of nanoparticles in zirconia microparticle suspension

Abstract

Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive forces between micro and nanoparticles at pH = 8 result in halo mechanism decrease and so the stability reaches its minimum. On the other hand, a different trend is observed when the suspension includes only the silica microparticles, maximum stability is at pH = 8, that is related to the higher electrical repulsive forces between microparticles, and it is minimum at pH = 5, because of attractive Van der Waals forces dominancy. Furthermore, the results show that more collision between the nanoparticles and microparticles results in more adsorption of nanoparticles and hence more suspension stabilization at every pH values. This can be attributed to the increased collision between nanoparticles resulting in more nanoparticles be trapped in the profound potential well close to the microparticle surface, and so a stronger nanoparticle halo will form. Besides, it revealed that the effect of the collision on the stability of suspension is more significant at pH = 5.