title: Co-ion and ion competition effects: ion distributions close to a hydrophobic solid surface in mixed electrolyte solutions.
abstract: We consider within a modified Poisson-Boltzmann theory an electrolyte, with different mixtures of NaCl and NaI, near uncharged and charged solid hydrophobic surfaces. The parametrized potentials of mean force acting on Na+, Cl-, and I- near an uncharged self-assembled monolayer were deduced from molecular simulations with polarizable force fields. We study what happens when the surface presents negative charges. At moderately charged surfaces, we observe strong co-ion adsorption and clear specific ion effects at biological concentrations. At high surface charge densities, the co-ions are pushed away from the interface. We predict that Cl- ions can also be excluded from the surface by increasing the concentration of NaI. This ion competition effect (I- versus Cl-) may be relevant for ion-specific partitioning in multiphase systems where polarizable ions accumulate in phases with large surface areas.
authors.affiliation: Escola de Química, Universidade Federal do Rio de Janeiro, Cidade Universitária, CEP 21949-900, Rio de Janeiro, RJ, Brazil.
authors.forename: E R A
authors.initials: ER
authors.lastname: Lima
authors.forename: M
authors.initials: M
authors.lastname: Boström
authors.forename: D
authors.initials: D
authors.lastname: Horinek
authors.forename: E C
authors.initials: EC
authors.lastname: Biscaia
authors.forename: W
authors.initials: W
authors.lastname: Kunz
authors.forename: F W
authors.initials: FW
authors.lastname: Tavares