Abstract
A systematic study of the effect of composition on the thermo-physical properties of the binary mixtures of 1-methyl-3-pentyl imidazolium hexafluorophosphate [MPI][PF6] with poly(ethylene glycol) (PEG) [Mw = 400] is presented. The excess molar volume, refractive index deviation, viscosity deviation, and surface tension deviation values were calculated from these experimental density, ρ, refractive index, n, viscosity, η, and surface tension, γ, over the whole concentration range, respectively. The excess molar volumes are negative and continue to become increasingly negative with increasing temperature; whereas the viscosity and surface tension deviation are negative and become less negative with increasing temperature. The surface thermodynamic functions, such as surface entropy, enthalpy, as well as standard molar entropy, Parachor, and molar enthalpy of vaporization for pure ionic liquid, have been derived from the temperature dependence of the surface tension values.
Highlights
Ionic liquids (ILs) are a group of organic salts that result from the combination of several organic cations and inorganic anions, and they may be liquid at room temperature
In an attempt to explore the nature of interactions occurring between the mixing components, we report here the density, viscosity, refractive index, and surface tension of the binary mixture PEG400 and 1-methyl-3-pentylimidazolium hexafluorophosphate [MPI][PF6] from 293.15 to 353.15 K at atmospheric pressure
The negative value for the binary system is due to the fact that the interaction through hydrogen bonding between the imidazolium ring of [MPI][PF6] and the oxygen lone pair of PEG400 is strong and has tightened the structure of the mixture; the filling effect of poly(ethylene glycol) (PEG) in the interstices of ILs and the ion-dipole interactions between the PEG polar compound and the imidazolium ring of the ILs are the contributors to the negative values of the molar excess volumes [36,37]
Summary
Ionic liquids (ILs) are a group of organic salts that result from the combination of several organic cations and inorganic anions, and they may be liquid at room temperature. The chemical and physical properties of ILs are interesting for several reasons, such as their high thermal stability, high conductivity, low density, extremely low vapor pressure, large electrochemical window, and their non-aqueous and non-toxic nature [2,3,4,5,6,7] These properties make ILs ideal for many applications including their use as reusable solvents in organic reactions, and as electrolytes in batteries and solar cells [8,9,10,11,12,13]. Zhang et al [18] determined the physical properties of the binary system of 1-ethyl-3-methyl imidazolium tetrafluoroborate +H2O Their results show that the densities and viscosities are strongly dependent on the water content and weakly dependent on the temperature.
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