On the dynamics of the lyophobic colloids

Abstract According to the standard theory, a spatially-extended (diffuse) double layer is assumed to occur in charged colloids (suspensions), leading to repulsive forces that might compensate, at relevant distances, the attractive molecular forces. It is shown in this paper that, in contrast with this standard double-layer theory, the electric interaction of the ions and the charged colloidal particles requires the application of the cohesion theory of electrically-interacting particles, which may lead to stabilization, or even aggregation of the colloid, independently of attractive molecular forces. The screened two-particle interaction which occurs in this case (in the dilute limit) is attractive at long distances and repulsive at short distances, with a negative minimum. Many-particle forces occur over short distances, which complicate considerably the situation. Solid and liquid phases are identified here in charged colloids (and even a non-ideal gaseous phase with attractive interaction), the equilibrium mean separation distance between the particles is estimated and the transition between various phases is discussed.