The degree of dissociation of ionic surfactant shells within a W/O microdroplet

The degree of dissociation of ionic surfactant shells within a W/O microdro plet is investigated on the basis of the Poisson-Boltzmann equation and loc ally ideal mixing assumption. The degree of dissociation is the result of t he competition between the entropy associated with counterions in the aqueo us core and mixing of surfactant ions with associated surfactants on the sh ell, and the electrostatic energy. The degree of dissociation is found to d epend on the geometry and is in the order: Two planar surfaces > cylinder > sphere of the same size. Moreover, for the same geometry, the degree of di ssociation increases with the size of the droplet. The free energy change a ssociated with a droplet due to dissociation is obtained. The effect of the solubilization of a neutral particle on the degree of dissociation is also studied. The solubilization is found to hinder the dissociation. (C) 2000 American Institute of Physics. [S0021-9606(00)70646-5].