Sedimentation of charged colloids in the gravitational field:: Relaxation toward equilibrium.

The sedimentation of charged colloids in the gravitational field is studied. It is found that the concentration of the colloidal particles obeys a linear equation. The assumptions used are : the colloid particles have a constant charge; the electroneutrality condition is verified locally. If the hard-sphere repulsion between the colloids is not taken into account, the problem can be studied in terms of relaxation times. The result depends on the initial conditions and the spatial localisation. It is found that it is not a simple relaxation since for example the process is not uniform The results are consistent with experimental studies. Lastly, the effect of added salt and the influence of the hard sphere repulsion are briefly examined. (C) 1999 Elsevier Science B.V. All rights reserved.