Densities, viscosities and derived thermophysical properties of water-saturated imidazolium-based ionic liquids

abstract

In order to evaluate the impact of the alkyl side chain length and symmetry of the cation on the thermophysical properties of water-saturated ionic liquids (ILs), densities and viscosities as a function of temperature were measured at atmospheric pressure and in the (298.15-363.15) K temperature range, for systems containing two series of bis(trifluoromethylsulfonyl)imide-based compounds: the symmetric [C(n)C(n)im][NTf2] (with n = 1-8 and 10) and asymmetric [C(n)C(1)im][NTf2] (with n= 2-5, 7, 9 and 11) ILs. For water-saturated ILs, the density decreases with the increase of the alkyl side chain length while the viscosity increases with the size of the aliphatic tails. The saturation water solubility in each IL was further estimated with a reasonable agreement based on the densities of water-saturated ILs, further confirming that, for the ILs investigated, the volumetric mixing properties of ILs and water follow a near ideal behavior. The water-saturated symmetric ILs generally present lower densities and viscosities than their asymmetric counterparts. From the experimental data, the isobaric thermal expansion coefficient and energy barrier were also estimated. A close correlation between the difference in the energy barrier values between the water-saturated and pure ILs and the water content in each IL was found, supporting that the decrease in the viscosity of ILs in presence of water is directly related with the decrease of the energy barrier. (C) 2015 Elsevier B.V. All rights reserved.

keywords

MUTUAL SOLUBILITIES; CATION SYMMETRY; AQUEOUS-SOLUTIONS; SURFACE-TENSION; MIXTURES; TEMPERATURE; IMPACT; PURE; DEPENDENCE; SALTS

subject category

Thermodynamics; Chemistry; Engineering

authors

Martins, MAR; Neves, CMSS; Kurnia, KA; Carvalho, PJ; Rocha, MAA; Santos, LMNBF; Pinho, SP; Freire, MG

Groups

G4 - Renewable Materials and Circular Economy
G5 - Biomimetic, Biological and Living Materials
G6 - Virtual Materials and Artificial Intelligence

Projects

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

Igy Technology: A Purication Platform using Ionic-Liquid-Based Aqueous Biphasic Systems (IGYPURTECH)

acknowledgements

This work was developed in the scope of the projects CICECO-Aveiro Institute of Materials (Ref. FCT UID/CTM/50011/2013) and LSRE/LCM-Laboratory of Separation and Reaction Engineering (Ref. FCT UID/EQU/50020/2013), financed by national funds through the FCT/MEC and when applicable co-financed by FEDER under the PT2020 Partnership Agreement. The authors also thank FCT for the doctoral and post-doctoral grants SFRH/BD/87084/2012, SFRH/BD/70641/2010, SFRH/BPD/88101/2012, SFRH/BPD/82264/2011 for M. A.R.M., C.M.S.S.N., K.A.K., and P.J.C., respectively. M.G.F. acknowledges the European Research Council (ERC) for the grant ERC-2013-StG-337753 and S.P.P. thanks a grant from FAPESB.