Topological Electric Double Layers in Charged Colloids

Charged surfaces in contact with liquids containing ions are accompanied in equilibrium by an electric double layer consisting of a layer of surface charge and a bulk ion cloud. This screening cloud determines not only the interactions between charged particles and their self-assembly [1], but also determines, for example, how the interaction of a charged colloidal particle with an interface can be tuned from attractive to repulsive [2]. However, little is known to what spatial complexity the electric double layers can be designed. Here, we show that electric double layers of non-trivial topology -including tori, multi-tori and knots- can be realised in charged colloids with complex-shaped particles, using numerical modelling. We show that the topology of double layers can be defined via a cut-off in the ion concentration and demonstrate that the double layer topology can be tuned by changing the Debye screening length or by changing the shape and topology of the particle [3]. This work is an attempt to introduce concepts of topology in the field of charged colloids.
[1] J.C. Everts, et al, Soft matter 12, 6610-6620
[2] J.C. Everts, S. Samin, R. van Roij, Phys. Rev. Lett. 117 (9), 098002
[3] J.C. Everts and M. Ravnik, Topological Electric Double Layers, submitted to Nat. Comm.