Viscosity of Ionic Liquids: An Extensive Database and a New Group Contribution Model Based on a Feed-Forward Artificial Neural Network

Abstract

A knowledge of various thermophysical (in particular transport) properties of ionic liquids (ILs) is crucial from the point of view of potential applications of these fluids in chemical and related industries. In this work, over 13 000 data points of temperature- and pressure-dependent viscosity of 1484 ILs were retrieved from more than 450 research papers published in the open literature in the last three decades. The data were critically revised and then used to develop and test a new model allowing in silico predictions of the viscosities of ILs on the basis of the chemical structures of their cations and anions. The model employs a two-layer feed-forward artificial neural network (FFANN) strategy to represent the relationship between the viscosity and the input variables: temperature, pressure, and group contributions (GCs). In total, the resulting GC-FFANN model employs 242 GC-type molecular descriptors that are capable of accurately representing the viscosity behavior of ILs composed of 901 distinct ions. The neural network training, validation, and testing processes, involving 90, 5, and 5% of the whole data pool, respectively, gave mean square errors of 0.0334, 0.0595, and 0.0603 log units, corresponding to squared correlation coefficients of 0.986, 0.973, and 0.972 and overall relative deviations at the level of 11.1, 13.8, and 14.7%, respectively. The results calculated in this work were shown be more accurate than those obtained with the best current GC model for viscosity of ILs described in the literature.

Functional Electro-materials Based on Ferricyanide Redox-active Ionic Liquids

“…It is also evident that the ferricyanide IL's viscosity is effectively independent of the preparation method over the entire temperature range studied which is a strong indication that the materials are either relatively pure, or, at worse, have very similar impurity profiles. A closer inspection of the data also demonstrates that they exhibit slight positive curvatures suggesting that the classical hydrodynamic Arrhenius theory does not apply which is a common observation for ionic liquids and other glass forming liquids [20]. In such cases, the temperature-viscosity relationship is likely to adhere to an alternative free volume model, typically the Vogel-Tamman-Fulcher expression is assume to be appropriate [20] (VTF, Equation 3).…”

“…A closer inspection of the data also demonstrates that they exhibit slight positive curvatures suggesting that the classical hydrodynamic Arrhenius theory does not apply which is a common observation for ionic liquids and other glass forming liquids [20]. In such cases, the temperature-viscosity relationship is likely to adhere to an alternative free volume model, typically the Vogel-Tamman-Fulcher expression is assume to be appropriate [20] (VTF, Equation 3). …”

“…Because dynamic events in liquids phases are frequently controlled by the rate of viscous flow processes the rheological properties of liquids materials is of the utmost importance -this is of particular consideration in electrochemical devices where ionic mobility, solvent reorganisation, and diffusional fluxes control the performance of the devices. The viscous behaviour of RTILs has been the subject of intense interest and scrutiny over many years [19,20]. Seddon et al [19] have shown that the presence of small quantities of imputes can have a dramatic effect on viscosity.…”

“…Seddon et al [19] have shown that the presence of small quantities of imputes can have a dramatic effect on viscosity. Gratzel et al [17] established the relationship between ionic conductivities and viscosities in RTILs, while Paduszyński and Domańska [20] reported the use of group contribution models for predicting RTIL viscosity. Given the large molecular mass and structural symmetry of the ferri-and ferro-cyanide ILs studied here, highly viscous behaviour is expected and, indeed, is found.…”

Imidazole-based ionic liquids for free radical photopolymerization

“…[42] As a representative monomer, 2-IL containing the ethyl spacer was tested in mixtures with HDDA. The amount of 2-IL in HDDA was varied from 0, 5, 10, 25 and 100 wt%.…”