Understanding the role of confinement in the behavior of ionic liquid–organic solvent mixtures in slit carbon micropores: Insights from molecular dynamics

Abstract

In this study, we used molecular dynamics simulations to investigate the effects of diluting [EMIM][NTf₂] with DMSO on the behavior of the electrolyte within negatively charged slit-like micropores. Our results demonstrate clear differences in electrolyte composition between confined and bulk phase. Increasing the DMSO content leads to higher concentrations of counterions within the pores, particularly in pores that are 0.7 and 0.9 nm wide. Oscillations in the disjoining pressure, excess charge in the center of the pore, and fluctuations in the number of hydrogen bonds occur as the pore size increases due to abrupt structural changes of the electrolyte inside the pores. Namely, the electrolyte arrangement within the pores adopts a layered structure, with a single layer in pores up to 0.9 nm wide and additional cation–anion layer forming with every 0.4 nm increase in width. This study offers insights into how confinement impacts the orientation and conformation of ions and solvent molecules within micropores. In particular, the distribution of cis- and trans-conformers of the [NTf₂]⁻ anions varies depending on the size of the pore.