Measurement And Correlation For Density Viscosity And Surface Tension Of Mixed Systems Containing Ionic Liquids And Alcohols Or Water

The physical properties including the density, viscosity and surfacetension for the binary mixtures of water （methanol or ethanol） with sevenimidazolium dialkylphosphates ionic liquids （ILs） have been studied. Thedensity and viscosity for the binary systems were measured in thetemperature range of （293.15to333.15） K at atmospheric pressure usingthe densimeter and viscometer, and the surface tension for the binarysystems were also measured at298.15K and313.15K using the surfacetensiometer. The effects of temperature, IL-content and other relevantfactors on density viscosity and surface tension of binary mixtures arediscussed. Besides, the density and viscosity of ILs with respect to theircorresponding molecular fluids and physical admixtures were measuredalso, whereby the influence of electrostatic interaction is discussed.First, seven imidazolium dialkylphosphates ILs are designed andsynthesized by one-step method, and their structure and purity are confirmed by NMR spectra and elementary analysis. The results show thatthe purities of seven ILs are estimated as x≥99.1%, and they can be usedfor the measurement of their corresponding physical properties.The results show that the densities of a mixture decrease slightly in alinear way with the increasing temperature or the alkyl chain length in theimidazole ring, and increase with the IL-content. Based on theexperimental data of density, some thermodynamic properties and excessmolar volumes （V^E） are derived. It is found that all V^Evalues are negativefor all binary mixtures studied in the whole composition range and quitelow being in the range of （1.0to1.9） cm³·mol^-1, and reach to the maximumat the mole fraction of IL being around0.3. The V^Evalues decrease withincreasing temperature for the aqueous solution of ILs, whilst a reversetrend is found for the IL solutions of methanol or ethanol at anyconcentration. The V^Evalues are correlated successfully by afive-parameter polynomial equation as a function of temperature and molefraction of IL, from which densities of the binary mixtures can berepresented accurately with the maximum average absolute relativedeviation within0.03%.The results for viscosity show that the viscosities of a mixturedecrease drastically with the increasing temperature and decreasingIL-content, and increase rapidly with the alkyl chain length in theimidazole ring of cation. The viscosities are correlated successfully by an eight-parameter empirical equation as a function of temperature and molefraction of IL. Besides, all the excess viscosities （η^E） are negative, and havea low-water mark in the viscosity-composition plot. Moreover, the η^Eforthe binary mixtures of IL plus methanol or ethanol are much higher thanthat of IL aqueous solution at any specific temperature.The results for density and viscosity of molecular liquids and theirequimolar physical mixtures for systhesing ILs show that the density andviscosity of the equimolar physical mixtures are always between theircorresponding pure molecular liquids, and the density and viscosity of ILsare always higher than those of the physical mixtures, for example, theviscosity of ILs is hundreds of times higher than the corresponding physicalmixtures, which is mainly originated from the electrostatic contraction.The results for surface tension show that the surface tensions of amixture decrease with the increasing temperature and the alkyl chain lengthin the imidazole ring of cation. However, the variations of the surfacetension of a binary mixture with the IL-content are quite different.This study on one hand enrich the experimental data base for the ILsrelated mixtures, on the other hand it is helpful to reveal the quantitativestructure-property relation and the interaction mechanism wherein, so as toprovide a solid foundation for the molecular design of a task-specific ionicliquid as well as for the large-scale application of ILs in industry.