Effect of the Surface Charge Discretization (Mobile Charge) on Electric Double Layer

Mirfit Mahmoud Amleh
ميرفت محمود العملة
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Al-Quds University
The structure of the electric double layer (EDL) in contact with discrete and continuously charged sphere macroion surfaces is studied within the framework of the primitive model through Monte Carlo simulations. Mobile charge discretization models (point charges localized on the macroion surface and finite-sized charges protruding into the solution) are considered together with the case of uniform charge distribution (central). The distribution of counterions near a macroion is determined using a spherical cell. The effect of discreteness is analyzed in terms of radial distribution functions, charge density profiles, and potential profiles. The effect of discretization, radius of the counterions and the presence of salt on the potential of EDL and accumulated charges are also studied. It is established that with protruding charges the counterions are less accumulated near the macroion because the excluded volume effect dominating over the increased correlation ability. But with point charges distributions, counterions become more strongly accumulated to the macroion and the effect increases with counterion valence. At low salt concentration, the macroion accumulated charge is reduced due to multivalent counterion adsorption. At high salt concentrations, the macroions become overcharged so that their apparent charge has the opposite sign to the stoichiometric one. The character of charge distribution affects the EDL structure near the macroion, whereas its effect is much weaker at larger distances.