On the fluid–fluid phase separation in charged-stabilized colloidal suspensions

Abstract

We develop a thermodynamic description of particles held at a fixed surface potential. This system is of particular interest in view of the continuing controversy over the possibility of a fluidfluid phase separation in aqueous colloidal suspensions with monovalent counterions. The condition of fixed surface potential allows in a natural way to account for the colloidal charge renormalization. In a first approach, we assess the importance of the so called "volume terms", and find that in the absence of salt, charge renormalization is sufficient to stabilize suspension against a fluid-fluid phase separation. Presence of salt, on the other hand, is found to lead to an instability. A very strong dependence on the approximations used, however, puts the reality of this phase transition in a serious doubt. To further understand the nature of the instability we next study a Jelliumlike approximation, which does not lead to a phase separation and produces a relatively accurate analytical equation of state for a deionized suspensions of highly charged colloidal spheres. A critical analysis of various theories of strongly asymmetric electrolytes is presented to asses their reliability as compared to the Monte Carlo simulations.

Liquid friction on charged surfaces: From hydrodynamic slippage to electrokinetics

“…(C8) (see [39,40] and references therein). At fixed ℓ B = σ, (C8) implies for monovalent microions Σσ 2 /e < 1, which is always fulfilled in the situations investigated in the present study.…”

The renormalized jellium model for spherical and cylindrical colloids

“…The boundary conditions are the same as (8) and (9), and the numerical method identical to that used in the spherical case.…”

“…Initially borrowed from solid state physics, the concept of a cell nevertheless appears fruitful to describe the phase behaviour of liquid phases (see e.g. [8]). When a more microscopic information such as effective interaction is sought, there is however to date no evidence that the cell picture provides accurate answers, through the approximate procedures that have been proposed to infer solvent and micro-ions averaged inter-colloid potentials of interaction [3].…”

Introduction to statistical mechanics of charged systems

“…(160), we see that C < 15 for all the values of the bare charge Z in the critical region. The critical threshold, therefore, can not be reached [71], meaning that a deionized aqueous suspensions with monovalent counterions is stable against a liquid-gas phase separation for all colloidal charges and sizes. This conclusion has also been confirmed by more detailed calculations and simulations [41,72,73,74,75].…”