Probing the distribution of ionic liquid mixtures at charged and neutral interfaces via simulations and lattice-gas theory

Room temperature ionic liquid solutions confined between neutral and charged surfaces are investigated by means of atomistic Molecular Dynamics simulations. We study 1-ethyl-3-methylimidazolium dicyanamide ([EMIm]⁺[DCA]^-) in water or dimethylsulfoxide (DMSO) mixtures in confinement between two interfaces. The analysis is based on the comparison of the molecular species involved and the charged state of the surfaces. Focus is given on the influence of different water/DMSO concentrations on the microstructuring and accumulation of each species. Thermodynamic aspects, such as the entropic contributions in the observed trends are obtained from the simulations using a lattice-gas theory. The results clearly underline the differences in these properties for the water and DMSO mixtures and unravel the underlying mechanisms and inherent details. We were able to pinpoint the importance of the size and the relative permittivity of the molecules in guiding their microstructuring in the vicinity of the surfaces, as well as their interactions with the latter, i.e. the solute-surface interactions. The influence of water and DMSO on the overscreening at charged interfaces is also discussed. The analysis on the molecular accumulation at the interfaces allows us to predict whether the accumulation is entropy or enthalpy driven, which has an impact in the removal of the molecular species from the surfaces. We discuss the impact of this work in providing an essential understanding towards a careful design of electrochemical elements.

Specific Ion Effects in Different Media: Current Status and Future Challenges

We discuss the current state of research as well as the future challenges for a deeper understanding of specific ion effects in protic and aprotic solvents as well as various additional media. Despite recent interest in solute or interfacial effects, we focus exclusively on the specific properties of ions in bulk electrolyte solutions. Corresponding results show that many mechanisms remain unknown for these simple media, although theoretical, computational, and experimental studies have provided some insights into explaining individual observations. In particular, the importance of local interactions and electronic properties is emphasized, which enabled a more consistent interpretation of specific ion effects over the past years. Despite current insufficient knowledge, we also discuss future challenges in relation to dynamic properties as well as the influence of different concentrations, different solvents, and solute contributions to gain a deeper understanding of specific ion effects for technological applications.