SURFACE-CHARGE DENSITY AND SURFACE-POTENTIAL CALCULATIONS OF A CHARGED SPHERE IN DISSYMMETRICAL ELECTROLYTES

The surface charge and surface potential of the dispersed particles permits to estimate their physico-chemical interactions and the stability of the suspension. In a practical case, the surface potential can reach very high values (+/- 100 to +/- 400 mV). In that case, the solution of Debye-Huckel equation becomes inaccurate. The same holds if the particle radius becomes very small (500 to 10 angstrom) and kappa-a < 100. In this latter case, it is the Poisson-Boltzmann equation implying the parity between a spherical particle and a plane surface which becomes unsuited. A more adapted and precise solution of the non linear Poisson-Boltzmann equation for charged spherical particles in the presence of dissymmetrical electrolytes is given. We established the relationships of the electrostatic potential PSI(x) and of the surface charge sigma-0 and demonstrated that electrolytes of trivalent anions [ (1 -3) and (2-3) ] give higher surface densities.