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The ionic density profiles and corresponding integrated charge distribution close to an aqueous interface carrying charged functional groups of different valences exposed to mixed-salt solutions of 1:1 and 3:1 electrolytes were computed by use of extensive Monte Carlo simulations within the framework of the primitive model. The influence of varying ion sizes on charge inversion was analyzed, along with the crucial role of electrostatic images arising from dielectric discontinuities. For small sizes of charged species, it was found that charge inversion is enhanced by the presence of multivalent interfacial groups. Moreover, dielectric images further intensify the degree of charge inversion despite strong depletion effects. In particular, the onset of charge inversion shifts closer to the nonaqueous phase if the surface charge density is sufficiently low. These observations are opposite to the general belief of image repulsion. When large-sized ions were considered, the degree of charge inversion was found to be independent of the structure of interfacial groups and to remain widely unaffected in the absence and presence of dielectric images. Overall, our results show that interionic excluded-volume interactions are an overwhelming factor in determining counterion condensation. In addition, the inclusion of ionic size asymmetry at weakly charged interface results in surface charge amplification, which becomes more pronounced with increasing valence of the interfacial groups. Our work emphasizes the fact that surface equilibria mainly result from a subtle balance between steric and charge correlations. [ABSTRACT FROM AUTHOR]

The blue-shifted C−D stretching vibrations (νCD) of deuteriated dimethyl sulfoxide (DMSO-d6) in mixtures of DMSO-d6/ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) were carefully investigated and compared with those in DMSO-d6/water. Results from FTIR studies indicate that the direct interaction of C−D···F between DMSO-d6and the anion [BF4−] plays a minor role in the blue-shift of νCDin the mixtures of DMSO-d6/IL. They also show that the indirect influence of the hydrogen bond formed by the nearby functional group SO with C2−H of the cation significantly contributes to the blue-shift of νCD, as can be inferred from the significant differences of the blue-shift in [Bmim][BF4] and 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([Bm2im][BF4]). In contrast, in the case of DMSO-d6/water mixtures, direct hydration of C−H···O between the methyl groups of DMSO-d6with the oxygen atom of water is mainly responsible for the blue shift of νCD. Furthermore, theoretical calculations revealed that charge migrations as well as rehybridization have a dominant effect on the blue-shift in both mixtures. [ABSTRACT FROM AUTHOR]