ELECTROSTATIC INTERACTIONS OF BODIES BEARING THIN DOUBLE-LAYERS .3. DISSIMILAR DOUBLE-LAYERS

A new numerical algorythm was used to calculate the electrostatic interaction forces between regularly shaped particles bearing thin double-layers immersed in an arbitrary electrolyte. Our numerical procedure enabled the solution of the nonlinear one-dimensional Poisson-Boltzmann (PB) equation in which the excluded volume effect is quantitatively considered for an arbitrary surface charge. Using these one-dimensional solutions (parallel-plate system) the electrostatic force of interaction between regularly shaped particles was calculated according to the modified Derjaguin summation method. Calculations were performed for plates and particles bearing dissimilar surface charge (heterointeractions) for simple electrolytes and electrolyte mixtures with constant charge and constant potential boundary conditions. From these solutions the range of validity of previously derived limiting analytical expressions was estimated. A significant role of trace amounts of higher valency electrolytes decreasing considerably the interaction force was confirmed.