Measurement And Research For Density Viscosity And Surface Tension Of Ionic Liquid System

In this work, physical properties (density, viscosity and surface tension) for a series of ionic liquids (ILs) have been measured and studied systematically. Density and viscosity values for the ILs, reactants and their corresponding equimolar mixtures are determined by Anton Paar DMA4500densimeter and AMVn viscometer, respectively. Surface tension data are measured by Wilhelmy plate method for the binary mixtures containing an ionic liquid of the imidazolium dialkylphosphate family and water (methanol or ethanol) at298.15K and atmospheric pressure. The experimental data are analyzed to discuss the influence of factors such as temperature, cation/anion structure and electrostatic interaction on the properties to lay a good foundation for the large scale industry application as well as the theoretical study of ILs-green solvent.Firstly, nineteen ILs in total of two kinds are prepared by one-step method. The first type APILs are synthesized of imidazole, pyridine with halogenated hydrocarbon under a certain temperature heating reflux by quaternary ammonium reaction. The second type PILs are synthesized of imidazole, ethanolamine with carboxylic acid through acid-base neutralization reaction. Their purities and structures are identified by1HNMR analysis and water content determination.From the density values, we can see that the density decreases linearly with increasing temperature for all ILs studied. The first type ILs results show that density of the bromides are higher than those of chlorides and for the same series of ILs with a common anion, their density always decreases with the increasing length of alkyl groups in the cations. However, it tends just the reverse for the hydroxyl ammonium ionic liquids. Besides, some related thermodynamic properties are estimated from the experimental data and the density values are correlated successfully by a simple linear equation with AARD(p) below0.015%.The viscosity values show that viscosity is sensitive to temperature, namely, a minor temperature increasement usually results in a significant reduction in viscosity, and the higher the viscosity, the more obvious the variation trend is. Whereas, the first type ILs results indicate that viscosity of the bromides are lower than those of chlorides and increases with the increasing length of alkyl groups in the cations for the same series of ILs with a particular anion. The viscosity for the second type ILs is generally lower, such as imidazolium formate ILs with just23.2879mPa-s as its highest viscosity. Moreover, Litovitz equation, a simple linear equation and Arrhenius equation are selected to correlate the data, and we find that for an ionic liquid, fitting results varies with the three equations, and among which Litovitz equation performs best.In order to explore the effect of electrostatic interaction on density and viscosity, some of the first type ILs are selected, whose density and viscosity are determined along with the reactants and their equimolar physical mixtures. The results show that at any specific temperature, density and viscosity for the physical mixtures are between those of the reactants and the ILs, furthermore, viscosity for the ILs decreases exponentially with increasing temperature and the corresponding reactants and their mixtures behave relatively moderate. Additionally, we find the activation energy Ea derived from Arrhenius equation follows the same order as the viscosity.It shows that the surface tension for any pure ionic liquid is between that of alcohol and water, namely, σalcohol<σIL<σwater, which may be attributed to the strong electrostatic interaction as well as the preferential orientation of IL in the interfacial layer. A new term-specific cohesive energy (SCE) is extracted, and a satisfactory correlation is found between surface tension and SCE. Besides, the enthalpy of vaporization△lgHmo, Hildebrand solubility parameter δH and the surface tension deviation δσ are estimated from the experimental data. We also have analyzed the surface tension behavior of the IL-water/methanol/ethanol binary systems, and find that ILs act as a surfactant in aqueous solution, but more like a conventional non-electrolyte component in the alcoholic solutions.