8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P5.38Wed 711:10-14:00Monte Carlo and Poisson Boltzmann studies ofheterogeneously charged colloids in an electrolyteJoost de Graaf, 1 Marjolein Dijkstra, 1 and Rene van Roij 11 Utrecht University, Princetonplein 1, 3584 CC, Utrecht, NetherlandsWe investigate the range in parameter space where regular Poisson-Boltzmann theory can beused to accurately describe the electric double layer around a heterogeneously charged sphericalparticle in a dielectric medium with added salt. The screening ion profiles, obtained by ensembleaveraging in Primitive Model NVT Monte Carlo simulations, form the basis for comparisonto those obtained by Poisson-Boltzmann calculations. We consider a Legendre-Fourier seriesexpansion of both density profiles, comparing each individual mode separately, to arrive atrigorous boundaries to the region for which Poisson-Boltzmann theory can be considered to beaccurate. Here, we show that there is a good correspondence between our results and previouswork, which deals with the finite-size effect of ions, nonlinearity, and strong coupling, for thecase of a homogeneously charged particle, as well as, field theoretical calculations in the planargeometry ext[1, 2]. We expand upon these results by considering charged Janus particles withone charged hemisphere and two oppositely charged hemispheres, respectively. Furthermore,we analyze the relation between the extension of the obtained density profiles and that ofapproximations commonly used in literature, namely a shifted point charge and a finite sizeddipole, both in Poisson-Boltzmann theory and in Yukawa approximation. We conclude that thetwo approximations inadequately capture the extension of the surface charge distribution. Theeffect of this mismatch on the phase behavior of such Janus particles is to be quantified in futurework.[1] H. Boroudjerdi et al., Phys. Rep. 416, 129 (2005).[2] O. Punkkinen et al., Euro. Phys. Lett. 82, 48001 (2008).38