Sedimentation profiles of charged colloids: Entropic lift and charge separationA.-P. Hynninen1, R. van Roij2 and M. Dijkstra1
1 Debye Institute, Soft Condensed Matter, Utrecht University Princetonplein 5, 3584 CC Utrecht, The Netherlands
2 Institute for Theoretical Physics, Utrecht University Leuvenlaan 4, 3584 CE Utrecht, The Netherlands
(Received 31 October 2003; accepted in final form 5 January 2004)
We present Molecular Dynamics simulations and Poisson-Boltzmann theory of sedimentation equilibrium of suspensions of charged colloids, treated at the level of the primitive model, including the co- and counterions (microions) explicitly. The simulations provide the first direct confirmation of the theoretical low-salt predictions of i) a macroscopic separation of colloidal and microionic charge, ii) an almost homogeneous electric field in the suspension, iii) a highly non-barometric colloid density distribution. These effects, which cannot be explained within the usual effective one-component picture, should be measurable experimentally.
82.70.Dd - Colloids.
05.20.Jj - Statistical mechanics of classical fluids.
61.20.Ja - Computer simulation of liquid structure.
© EDP Sciences 2004