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Sedimentation of binary mixtures of like- and oppositely charged colloids: the primitive model or effective pair potentials?

M. Dijkstra·J. Zwanikken·R. van Roij
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Abstract

We study sedimentation equilibrium of low-salt suspensions of binary mixtures of charged colloids, both by Monte Carlo simulations of an effective colloids-only system and by Poisson-Boltzmann theory of a colloid-ion mixture. We show that the theoretically predicted lifting and layering effect, which involves the entropy of the screening ions and a spontaneous macroscopic electric field [J. Zwanikken and R. van Roij, Europhys. Lett. {\bf 71}, 480 (2005)], can also be understood on the basis of an effective colloid-only system with pairwise screened-Coulomb interactions. We consider, by theory and by simulation, both repelling like-charged colloids and attracting oppositely charged colloids, and we find a re-entrant lifting and layering phenomenon when the charge ratio of the colloids varies from large positive through zero to large negative values.

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M. Dijkstra, J. Zwanikken, R. van Roij. 2005-12-22. Sedimentation of binary mixtures of like- and oppositely charged colloids: the primitive model or effective pair potentials?. https://doi.org/10.1088/0953-8984%2F18%2F3%2F005

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