On the stability of concentrates. Non-aqueous dispersions

Abstract

It is demonstrated that the depth of the potential well between two colloidal particles which interact via van der Waals interactions can be minimized if they are covered with a shell of adsorbed surfactant molecules whose Hamaker constant is near to that or the liquid medium. This result is used to explain some experimental observations (I. Sushumna, R.P. Gupta and E. Ruckenstein, J. Mater. Res., 7 (1992) 2884) which indicate that long-chain fatty acids with an alkyl side chain of 5–10 carbon atoms located far from the head group of the surfactant lead to lower paste viscosities than those without side chains or with longer side alkyl chains. It is also suggested that, in concentrated suspensions, the collective interactions when the pair interaction is attractive can lead to an effective repulsion component between two neighboring particles, and that this effect may contribute to the stability of the concentrated dispersions.