The Debye-Hückel theory is covered in almost all textbooks on electrolyte solutions,1,2 but it will be reviewed in this chapter as a tool for modeling the interaction between charged colloidal particles of larger size. Because electrolytes in aqueous solution dissociate into ionic species that interact electrostatically, the concentration dependence of the activity coefficient differs sharply for electrolyte and nonelectrolyte solutions. This section is devoted to estimating the interaction between ionic species and deriving their activity coefficients. Three assumptions are adopted: (1) a solution is a dielectric continuum of constant ε; (2) ions are hard spheres of diameter a; and (3) the concentration is relatively low (at higher concentrations the Debye-Hückel theory is very approximate). Consider a charge density in a volume element dv at a distance r from an arbitrarily selected central ion and assume the mean electrostatic potential to be ψ r .
KeywordsActivity Coefficient Diffuse Layer Colloidal Particle Interparticle Distance Diffuse Double Layer
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