MECHANISMS BEHIND CONCENTRATION PROFILES ILLUSTRATED BY CHARGE AND CONCENTRATION DISTRIBUTIONS AROUND IONS IN DOUBLE-LAYERS

The mechanisms behind the behaviour of concentration and charge densit y profiles in diffuse electric double layers are investigated quantita tively for 1:1 and 2:2 electrolytes. This is done by analysing various contributions to the mean force that acts on each ion. The forces are obtained from the calculated ionic charge and concentration distribut ions around individual ions at various positions in the double layer. These distributions are presented graphically which allows an immediat e visual illustration of the mechanisms in action. Some features studi ed are charge inversion in double layers for divalent aqueous electrol ytes, overcompensation of surface charge due to large amounts of physi sorbed counterions, ion size effects in the double layer structure and various mechanisms that cause deviations from the predictions of the Poisson-Boltzmann approximation. A major objective of the paper is to present the results in a visual form and explain aspects of modern dou ble layer theory in a simple manner. (C) 1998 Elsevier Science S.A. Al l rights reserved.