Computational Studies of [bmim][PF₆]/n-Alcohol Interfaces with Many-Body Potentials

Abstract

In this paper, we present the results from molecular dynamics simulations of the equilibrium properties of liquid/liquid interfaces of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and simple alcohols (i.e., methanol, 1-butanol, and 1-hexanol) at room temperature. Polarizable potential models are employed to describe the interactions among species. Results from our simulations show stable interfaces between the ionic liquid and n-alcohols, and we found that the interfacial widths decrease from methanol to 1-butanol systems and then increase for 1-hexanol interfaces. Angular distribution analysis reveals that the interface induces a strong orientational order of [bmim] and n-alcohol molecules near the interface, with [bmim] extending its butyl group into the alcohol phase, whereas the alcohol has the OH group pointing into the ionic liquid region, which is consistent with the recent sum-frequency-generation experiments. We found the interface to have a significant influence on the dynamics of ionic liquids and n-alcohols. The orientational autocorrelation functions illustrate that [bmim] rotates more freely near the interface than in the bulk, whereas the rotation of n-alcohol is hindered at the interface. Additionally, the time scale associated with the diffusion along the interfacial direction is found to be faster for [bmim] but slowed down for n-alcohols approaching the interface. We also calculate the dipole moment of n-alcohols as a function of the distance normal to the interface. We found that, even though methanol and 1-butanol have different dipole moments in bulk phase, they reach a similar value at the interface.

An Empirical Polarizable Force Field Based on the Classical Drude Oscillator Model: Development History and Recent Applications

“…The most notable example of an induced dipole model is the AMOEBA force field, , which also includes multipoles up to quadrupoles in the treatment of the electrostatic interactions. Other induced dipole models include those presented by Berne, Friesner, and co-workers, , as well as the POSSIM model, among others. − …”

Force Fields for Small Molecules

“…In addition, the impact of polarization on more accurate treatment of nonpolar moieties such as those in the interior of membranes has been noted. Towards overcoming this limitation, parameters for organic small molecules based on polarizable force fields have started to be developed, dominated by the AMOEBA and Drude models as well as the work of Dang and coworkers [103–105, 208–213]. This chapter focused on the small molecule polarizable force fields based on the classical Drude oscillator model, which utilizes Drude oscillators on non-hydrogen atoms to generate the induced dipole in the context of an intuitive physical picture to model the electronic distribution.…”

“…The induced point dipole model has been used in several polarizable force fields, including OPLS/PFF [95], AMBER [96–100], and PIPF [101] as well as force fields developed by Berne, Friesner, and co-workers [95, 102], in the water, ion, and small molecule force field of Dang and coworkers [103–105], and others [106–109]. Ren and Ponder combined the induced dipole model with atomic multipoles through the quadrupole moments in the treatment of the electrostatic interactions in the context of the AMOEBA force field [110–112].…”

Promotional effect of ionic liquids in electrophilic fluorination of methylated uracils

“…35 and the uorination is expected to proceed at these interfaces. 35 and the uorination is expected to proceed at these interfaces.…”