Enhanced charge reversal and charge amplification in a shape- and size-asymmetric electric double layer: the effect of big ions
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In this paper, we present a Monte Carlo simulation study on the charge distribution and structure of a shape- and size-asymmetric electric double layer around a spherical colloid. Specifically, the macroparticle is surrounded by a binary electrolyte composed of spherical and spherocylindrical ions, where the excluded volume of the spherocylinders is considerably larger than that of the electrolytic spheres. We have used spherocylinders of low aspect ratio (Formula presented.), a sphere-spherocylinder ionic size asymmetry of (Formula presented.) and a colloid-spherocylinder size asymmetry of (Formula presented.). Results are presented for the local integrated charge and the colloid-ion radial distribution functions, considering several salt concentrations and charged states of the macroparticle. The conditions used here produce integrated charge profiles that are strongly oscillatory, with alternating layering regions of very large charge reversal and charge amplification (or overcharging), in a sequence that depends on the ionic identity of the spherocylinders. Such phenomenology is particularly visible in the regime of low colloidal charge, and it is mainly driven by the characteristics of the non-spherical ions and the size asymmetry between the ionic species. For weakly electrified macroions, the innermost region of anomalous charge has the largest amplitude and reaches absolute values of more than 15 times the native colloidal charge. © 2020, © 2020 Informa UK Limited, trading as Taylor %26 Francis Group.
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