Effect of a dynamic stern layer on the sedimentation velocity and potential in a dilute suspension of colloidal particles

In this paper the theory of the sedimentation velocity and potential (gradi ent) in a dilute suspension of charged spherical colloidal particles develo ped by Ohshima et al. (H. Ohshima, T. W. Healy, L. R. White, and R. W. O'Br ien, J. Chem. Sec., Faraday Trans. 2, 80, 1299 (1984)) has been modified to include the presence of a dynamic Stern layer on the particle surfaces. Th e starting point has been the theory that Mangelsdorf and White (C. S. Mang elsdorf, and L. R. White, J. Chem. Sec., Faraday Trans. 86, 2859 (1990)) de veloped to calculate the electrophoretic mobility of a colloidal particle a llowing for the lateral motion of ions in the inner region of the double la yer (dynamic Stern layer). The effects of varying the different Stern layer parameters on the sedimentation velocity and potential are discussed and c ompared to the case when a Stern layer is absent. The influence of electrol yte concentration and zeta potential of the particles is also analyzed. The results show that regardless of the chosen set of Stern layer and solution parameters, the presence of a dynamic Stern layer causes the sedimentation velocity to increase and the sedimentation potential to decrease, in compa rison with the standard case (no Stern layer present). These changes are al most negligible when sedimentation velocity is concerned, but they are very important when it comes to the sedimentation potential. A justification fo r this fact can be given in terms of an Onsager reciprocal relation, connec ting the magnitudes of the sedimentation potential and the electrophoretic mobility. As previously reported, the presence of a dynamic Stern layer exe rts a great influence on the electrophoretic mobility of a colloidal partic le, and by means of the Onsager relation, the same is confirmed to occur wh en the sedimentation potential is concerned. (C) 2000 Academic Press.