Charge-stabilized colloidal suspensions. Phase behavior and effects
R. Klein and H. H. von Grünberg
Fachbereich Physik, Universität Konstanz, 78457
Abstract: The PoissonBoltzmann (PB) equation is used to
investigate effective colloid-interface interactions and the phase behavior
of charge-stabilized colloidal suspensions. When a colloidal particle,
immersed in an electrolyte, approaches an interface, which may be neutral
(such as air) or charged (like electrodes, glass, etc.), image charge
effects plus the deformation of the colloidal ion atmosphere by the
interface lead to an effective interaction which can be attractive or
repulsive, depending on the surface charge density and the dielectric
constants of the interface and the electrolyte. Two cases are considered:
i) a spherical particle near a like-charged interface, and ii) a rod-like
particle in the vicinity of an oppositely charged interface. The latter
serves as a model for the adsorption of (anionic) DNA on a cationic
membrane, and it is shown that the effective attraction, induced by
the release of counterions on approach of the DNA to the membrane, makes
up an essential contribution to the total DNA-membrane effective interaction.
To understand the phase behavior of charge-stabilized colloidal suspensions,
we study a PB cell model of a bulk suspension and investigate how the
PB equation can best be linearized. It is found that the previously
predicted gasliquid phase coexistence results when the PB equation
is linearized about the Donnan potential. No indication of such a spinodal
instability could, however, be found, when the free energy is evaluated
using the numerical solution of the full PB equation. This suggests
that the predicted gasliquid phase coexistence is an artifact
of the linearization.
* Plenary lecture presented at the 27th International
Conference on Solution Chemistry, Vaals, The Netherlands, 26-31 August
2001.Other presentations are published in this issue, pp. 1679-1748.
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