Abstract
In this work, the effect of molecular cosolvents tetraethylene glycol dimethyl ether (TEGDME) on the structure and versatile nature of mixtures of these compounds with imidazolium-based ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) is analyzed and discussed at a molecular level by means of all-atom molecular dynamics (MD) simulations. In the whole concentration range of the binary mixtures, the structures and properties evolution was studied by means of systematic molecular dynamics simulations of the fraction of hydrogen bonds, the radial and spatial distribution functions for the various molecular ions and molecular species in the system, together with the snapshots visualization of equilibrated simulation boxes with a color-coding scheme and the rotational dynamics of coumarin 153 (C153) in the binary mixtures. The goal of the work is to provide a molecular-level understanding of significant improvement of ionic conductivity and self-diffusion with the presence of TEGDME as a cosolvent, which causes an enhancement to the ion translational motion and fluidity in the [bmim][PF6] ionic liquids (ILs). Under a mixture concentration change, the microstructure changes of [bmim][PF6] with the TEGDME molar fraction (XTEG) above 0.50 show a slight difference from that of neat [bmim][PF6] IL and concentrated [bmim][PF6]/TEGDME mixture in terms of the radial and spatial distribution functions. The relative diffusivities of solvent molecules to cations as a function of concentration were found to depend on the solvent but not on the anion. A TEGDME increase is found to be advantageous to the dissipation of the polar regions as well as the nonpolar regions in the [bmim][PF6] ionic liquids. These conclusions are consistent with the experimental results, which verified that the unique, complex, and versatile nature of [bmim][PF6]/TEGDME mixture can be correctly modeled and discussed at a molecular level using MD simulation data.
Highlights
In the past decade, room temperature ionic liquids have attracted extensive attention in academia and industry [1,2]
The most relevant thermophysical properties of [bmim][PF6 ] + tetraethylene glycol dimethyl ether (TEGDME) mixture are predicted as a function of the composition of the mixture and compared with the available experimental information
The structural, dynamical, transport, and thermodynamic properties for the binary mixtures of the ([bmim][PF6 ]) ionic liquids (ILs) with TEGDME solution have been calculated over the whole concentration range at T = 300−353 K and atmospheric pressure p = 1 atm
Summary
Room temperature ionic liquids have attracted extensive attention in academia and industry [1,2]. An appropriate strategy to solve these problems and possibly adjust the performance of ionic liquids (ILs) is to mix them with simple, inexpensive, and low-weight molecular cosolvents. In this way, by properly selecting IL, cosolvent, and their appropriate molar fraction, the optimal design of such mixtures can be carried out, which leads to the decrease in Nanomaterials 2021, 11, 2512. Nanomaterials 2021, 11, 2512 viscosity and generally expands various properties, opening up new application fields and wider operating conditions. We need detailed information about the composition of mixtures and the target properties of such binary mixtures
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