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Workshops

Interactions and Transport of Charged Species in Bulk and at Interfaces

July 4, 2016 to July 7, 2016
Location : CECAM-AT

Charged colloids in bulk oil and near oil-water interfaces: charge regulation, re-entrant melting, and alternating strings

Rene van Roij
Utrecht University, The Netherlands

Coauthor(s) : J. C. Everts, N. Boon, S. Samin, M. van der Linden, A. Van Blaaderen
Department of Physics, Utrecht University, The Netherlands

Abstract

We will first consider bulk dispersions of charge-regulating colloids in oily solvents with long Debye lengths, and show on the basis of a new, simple, and accurate crystallisation criterion that the experimentally observed phase sequence fluid-bcc-fluid (i.e. re-entrant melting) with increasing colloidal packing fraction is only possible if a competition between anion and cation adsorption takes place on the colloidal surfaces [1]. The interaction of these colloids with a planar oil-water interface is then shown to be highly tuneable from attractive to repulsive, either by varying the sign of the colloidal charge via charge regulation, or by varying the difference in hydrophilicity between the dissolved cations and anions [2]. We also theoretically study the experimentally observed alternating strings in like-charged binary colloidal mixtures, which we explain in terms of charge-regulation induced effective dipoles [3]. If time permits we will finally touch upon the surface tension of an “electrified” oil-water interface that is sandwiched between two planar electrodes. We will explain how the double-layer structure and the tension of this interface can be modified by the electrodes even if they are at macroscopic distances (much larger than the Debye lengths) from the interface because of a new and possibly huge new length scale that appears in these systems in the case of large Gibbs transfer energies of all ion species involved [4].



References

[1] J.C. Everts, N. Boon, and R. van Roij, Phys. Chem. Chem. Phys. 18, 5211-5218 (2016).
[2] J.C. Everts, S. Samin, and R. van Roij, submitted, arXiv:1603.08703
[3] J.C. Everts, M. van der Linden, A. Van Blaaderen, and R. van Roij, in preparation.
[4] M. Westbroek, N. Boon, and R. van Roij, Phys Chem Chem Phys. 17, 25100 (2015).