Gas-liquid phase coexistence in colloidal suspensions?

Abstract

We describe a charge-stabilized colloidal suspension within a Poisson-Boltzmann
\ncell model and calculate the free energy as well as the compressibility as a function of colloidal
\ndensity. The same quantities are also calculated from the linearized Poisson-Boltzmann
\nequation. Comparing nonlinear with linear theory, we test the quality of different linearization
\nschemes. For concentrated suspensions, linearization about the Donnan potential is shown
\nto be preferable to standard Debye-H¨uckel linearization. We also show that the volume term
\ntheory proposed earlier follows from a linearization about the Donnan potential. Using this linearization
\nscheme, we find a gas-liquid phase coexistence in linear, but not in nonlinear theory.
\nThis result may imply that predictions of a spinodal instability in highly de-ionized colloidal
\nsuspensions are spurious.