Measurement and Correlation of Density, Viscosity, and Surface Tension for Imidazolium Bromide Ionic Liquids [CnMIM]Br (n=2,3, 4) Aqueous Solutions

The density, viscosity, and surface tension of aqueous solutions containing three imidazolium bromine ionic liquids (ILs) [CnMIM]Br with different alkyl chain lengths (n = 2,3,4) are determined within the temperature ranging from 283.15 to 343.15 K and at ambient pressure, respectively. The effect of the alkyl chain length of the imidazolium cation on the properties of the solutions is investigated. The experimental density and viscosity are satisfactorily described with the linear model and the Vogel- Tammann-Fulcher type equation, respectively. On the basis of the experimental data, the energy barrier and the surface entropy/enthalpy are calculated. The results show that the density and surface tension of aqueous ILs solution decrease and the viscosity increases with the increase of carbon atom number in imidazole ring carbon chain under the same conditions. The surface ordering in each aqueous solution follows [C2MIM]Br > [C3MIM]Br > [C4MIM]Br. The calculation of the molecular/ionic cluster interaction energy shows that there is a strong interaction between IL and water molecules, and the strong interaction between water and bromine ions is the main factor determining the properties of the solution. The data and results can provide a reliable support for the design and process calculation of chemical absorption cycle with water/IL working pairs.

Automated summary

This study determined the density, viscosity, and surface tension of aqueous solutions containing three different alkyl chain lengths (n = 2, 3, 4) of imidazolium bromine ionic liquids (ILs) [CnMIM]Br within a specific temperature and pressure range. The effect of the alkyl chain length on the properties of the solutions was investigated. The experimental data showed that the density and surface tension of the aqueous ILs solution decreased, while the viscosity increased with the increase in carbon atom number in the imidazole ring carbon chain. The strong interaction between IL and water molecules, as well as the interaction between water and bromine ions, were found to be the main factors determining the properties of the solution. These findings provide reliable support for the design and process calculation of chemical absorption cycles using water/IL working pairs.