Charged Colloids

Introduction

Colloidal solutions contain mesoscopic particles, the colloids, in the nanometer to micrometer size range, and small solvent and additional solute molecules. In presence of polar solvent, mainly water, the colloidal surfaces carry charges by ionization of surface groups or adsorption of bulk ions and the solution becomes a very asymmetrical mixture of charged colloids, counterions (ions of sign opposite to the colloidal charge, which must always be present in order to satisfy the whole electroneutrality of the solution), and coions(of same sign, which appear, for instance, by adding salt), all immersed in a structured, dielectric solvent. The structural, equilibrium, thermodynamical properties of such colloidal systems are mainly governed by excluded volume and coulombic couplings existing between the different species. Conceptually, they could be viewed as a multivalent electrolyte, the colloid playing the role of an ion of high valence, but it is clear that all...