R. Messina et al 2002 Europhys. Lett. 60 383 doi:10.1209/epl/i2002-00275-y
R. Messina1, E. González-Tovar2,3,4, M. Lozada-Cassou2,4 and C. Holm1
Show affiliationsIn this letter we investigate the mechanism for the overcharging of a single spherical colloid in the presence of aqueous salts within the framework of the primitive model by molecular dynamics (MD) simulations as well as integral-equation theory. We find that the occurrence and strength of overcharging strongly depends on the salt-ion size, and the available volume in the fluid. To understand the role of the excluded volume of the microions, we first consider an uncharged system. For a fixed bulk concentration we find that upon increasing the fluid particle size one strongly increases the local concentration nearby the colloidal surface and that the particles become laterally ordered. For a charged system the first surface layer is built up predominantly by strongly correlated counterions. We argue that this is a key mechanism to produce overcharging with a low electrostatic coupling, and as a more practical consequence, to account for charge inversion with monovalent aqueous salt ions.
87.15.Aa Theory and modeling; computer simulation
61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc.
Issue 3 (November 2002)
Received 31 May 2002, accepted for publication 22 August 2002, in final form 22 August 2002
R. Messina et al 2002 Europhys. Lett. 60 383
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