Surface Behavior of the 1-Bromobutane with Isomeric Butanol Mixtures

Evidence for Ion Association at the Gas-Liquid Interface of the Mixture of 1-Butyl-3-methylimidazolium Hexafluorophosphate and Benzonitrile: A Sum Frequency Generation Spectroscopy and Surface Tension Study

The gas-liquid interface for the mixtures of [BMIM][PF₆] and benzonitrile is studied by sum frequency generation (SFG) spectroscopy and surface tension measurements as an important solute to reduce the viscosity of ionic liquids. Solvation of ionic compounds in bulk solvent is not necessarily the same as that at the surface due to the lower dielectric medium at the air/liquid interface. The results from the temperature-dependent SFG spectroscopy and surface tension study suggest that the ionic liquid in a benzonitrile solvent is associated as ion pairs at the surface rather than as dissociated─solvated─ions in the bulk solution. The influence of ionic liquids on the surface structure of benzonitrile is investigated from 0 to 1.0 mole fraction of benzonitrile. The CH stretching mode of vibration of benzonitrile in the SFG spectrum begins from a 0.2 mole fraction (x) of benzonitrile, and the intensity of the peak constantly increases on increasing the concentration of benzonitrile. However, the addition of benzonitrile does not result in extra peaks or shifting of the peak frequency to the spectra of [BMIM][PF₆]. The surface tension measurements further support the presence of benzonitrile at the gas-liquid interface. The surface tension data of the mixture smoothly decrease as the benzonitrile concentration increases. The apparent tilt angle of the terminal methyl group of the cation of [BMIM][PF₆] is calculated from SFG polarization spectra and shows an apparent lowering with the addition of benzonitrile. The effect of temperature on the surface structure of the binary mixture is also reported at four different temperatures between -15 and 40 °C for both the SFG spectroscopy and surface tension study. Benzonitrile shows different behavior in the mixture at higher temperatures than pure benzonitrile, as observed in the SFG spectra. In contrast, it does not show any CN peak in the mixture below 0.9 mole fraction. The temperature dependence of the interfacial tension is used to evaluate thermodynamic functions such as surface entropy and surface enthalpy. Both were found to be lowered with the increasing concentration of benzonitrile. Both spectroscopic and thermodynamic analyses indicate that the ionic liquid is highly associated as ion pairs and the benzonitrile is more ordered at the surface at concentration <0.4×.

Phase equilibrium of binary mixtures of cyclic ethers + chlorobutane isomers: experimental measurements and SAFT-VR modeling

The phase equilibria (experimental and modeled) of eight binary mixtures each formed by a cyclic ether (1,3-dioxolane or 1,4-dioxane) and a chlorobutane isomer (1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, or 2-chloro-2-methylpropane) are presented. New experimental vapor-liquid equilibrium data at isothermal conditions (298.15, 313.15, and 328.15 K) has been obtained, and the statistical associating fluid theory for potentials of variable range (SAFT-VR) is used to model the mixtures. The results are discussed in terms of both the molecular characteristics of the pure compounds and the unlike intermolecular interactions present in the mixtures. The SAFT-VR approach is first used together with standard combining rules without adjustable parameters in order to predict the phase behavior at isothermal conditions. Good agreement between experiment and the prediction is found with such a model. Mean absolute deviations for pressures lie between 1 and 3 kPa, while for vapor phase compositions are less than 0.03 in mole fraction. However, a better agreement, can be obtained by introducing one adjustable parameter kij, which modifies the strength of the dispersion interaction between unlike components in the mixtures. This parameter is adjusted so as to model the phase equilibrium of the whole family of mixtures studied here at isothermal and isobaric conditions. We find that a unique unlike parameter kij is valid for all the studied mixtures and it is not temperature or pressure dependent. This unique transferable parameter together with the SAFT-VR approach provide a description of the vapor-liquid equilibrium of the mixtures that is in excellent agreement with the experimental data. In this case, the absolute deviations are of the order of 0.001 in mole fraction for vapor-phase compositions and less than 1 kPa for pressure.

Study of Weak Molecular Interactions through Thermodynamic Mixing Properties

The electron donor-acceptor abilities of some cyclic ethers (tetrahydropyran or tetrahydrofuran), benzene, and halobenzenes (fluorobenzene or chlorobenzene) and the molecular interactions between these compounds have been investigated through a wide set of thermodynamic mixing properties of their mixtures. The mixing properties have been derived from experimental measurements of density, speed of sound, refractive index, surface tension, heat of mixing, and vapor-liquid equilibrium at the temperature of 298.15 K.