On the molecular mechanism of surface charge amplification and related phenomena at aqueous polyelectrolyte-graphene interfaces

摘要

In this communication we illustrate the occurrence of a recently reported newphenomenon of surface-charge amplification, SCA, (originally dubbedovercharging, OC), [Jimenez-Angeles F. and Lozada-Cassou M., J. Phys. Chem. B,2004, 108, 7286] by means of molecular dynamics simulation of aqueouselectrolytes solutions involving multivalent cations in contact with chargedgraphene walls and the presence of short-chain lithium polystyrene sulfonateswhere the solvent water is described explicitly with a realistic molecularmodel. We show that the occurrence of SCA in these systems, in contrast to thatobserved in primitive models, involves neither contact co-adsorption of thenegatively charged macroions nor divalent cations with a large size and chargeasymmetry as required in the case of implicit solvents. In fact the SCAphenomenon hinges around the preferential adsorption of water (over thehydrated ions) with an average dipolar orientation such that the charges of thewater's hydrogen and oxygen sites induce magnification rather than screening ofthe positive-charged graphene surface, within a limited range of surface-chargedensity.