E-mail: garcia. For this purpose, we have studied the structure as well as the estimations of several properties of one ionic liquid IL. These estimations are obtained from polarization charge distribution in which the IL is embedded. Special attention has been paid to the effect of the dielectric constant value in the predictions. For this purpose, polarization charge density has been modeled using several values of dielectric constant, and properties have been estimated in each case.
The influence of the length of the alkyl chain of ionic liquid in the estimation of these properties has also been tested. Finally, the results have been compared with experimental data. However, in order to be useful as solvents, these favorable features must overcome the less favorable transport properties, related to their high viscosity and surface tension.
Contributions from IDS members
Thus the choice of a particular IL for a given application requires the improvement of several design parameters. This fact can become a cumbersome process due to the huge number of possible combinations between ions. The combination of cation—anion pairs 28,29 and the molecular structure of the ions 30,31 affect to the properties of ILs, and therefore must be considered in the selection process. Furthermore, specific structural aspects as the length of alkyl chain substituents 32,33 can be used for tuning ILs for specific purposes.
Because of this, ILs have been termed designer solvents. In order to facilitate a first selection, theoretical methods can be useful since they are usually faster and cheaper than experimental procedures.
Process simulation is one of such methods, which proves to be a powerful tool to make predictions on the performance of systems in the equipment environment. Some of them are difficult to measure even impossible in some cases like with normal boiling temperatures. In these cases, reliable theoretical estimations could be used as input to the simulator.
Importance of liquid fragility for energy applications of ionic liquids
Computational methods provide a possible alternative in terms of means for quantitative theoretical predictions of thermochemical properties. Given the nature of the problem, methods based on quantum treatments may be preferable, but most of them have been devised to deal with single molecules or clusters of relatively few molecules. This is insufficient for a good description of liquid phases. In COSMO 40 model the starting point of COSMO-RS treatment , the effect of environment on a given molecule is simulated in terms of a polarization charge density located on the surface of a cavity surrounding the molecule.
The cavity is built by a superposition of spheres centered at the nuclei of the molecule with radii which usually are taken as 1. The charge density is determined with the condition that the total electric field or, alternatively, its electrostatic potential vanishes over the cavity surface. When applying COSMO-RS, it is customary to take the polarization charge density corresponding to a molecule whose electron density corresponds to the molecule placed in vacuum. However, real molecules are embedded in a more or less polarizable medium, and this fact should be taken into account.
One way to introduce this effect is to use a Polarizable Continuum Model PCM , 42 with a given value of the dielectric constant, when computing the electric field or electrostatic potential which determine the polarization charge density. ILs based on imidazolium cations have been proposed as good solvents in separation processes because the aromatic or aliphatic character of the liquid can be tuned by modifying the alkyl chain length.
In particular, predictions have been made for vapor pressure as a function of temperature, and vaporization enthalpy, density, and viscosity at Finally, the results thus obtained have been compared with available experimental data. It has been reported that values of dielectric constant higher than 80 show insignificant variations in properties. To illustrate the influence of the dielectric constant in the results, Table 1 collects the values of interaction energy of ion pair, defined as the difference of total electronic energy between models, i.
In this table, we have also collected the distance between the proton placed between hydrogen nuclei in imidazolium and the nitrogen of NTf 2 , as a measure of the anion—cation distance. It can be seen that this distance increases as medium polarizability increases when CA model is considered. This behavior is similar for all ILs. Thus, we can determine the activation energy of conductivity both for different nanocomposite phases and for different design of the cells. Let us consider the glassy phase first. The activation energy E a decreases with the concentration of NPs in both directions of the charge transport along and across to the cation-anion layers.
The activation energy increases with the concentration of both semiconductor and metal NPs.
Dielectric Properties of Ionic Liquids
This may be due to the formation of additional charge trapping centers. In contrary with previous case, the conductivity across the cation-anion layers decreases with the concentration of the NPs. This result can be explained if we imagine that the charge that is traveling across the cation-anion layers of matrix is pushed between molecules of alkanoate chain. Thus, the mobility of the carriers gets higher with the increase of the number of areas where the close package of the alkanoate chains is deformed.
Thus, the higher concentrations of NPs provide higher mobility of the cadmium cations across the cation anion layers. The anisotropy of conductivity in the smectic phase of the nanocomposites is smaller than that in the glassy state. With an increase of the NPs concentration, the conductivity anisotropy increases for the smectic phase and decreases for the glassy phase.
Dependence of the anisotropy of the conductivity on the concentration of CdS and Au nanoparticles in glassy phase. Dependence of the anisotropy of the conductivity on the concentration of CdS and Au nanoparticles in smectic phase. While the temperature is far from the phase transition and the dielectric permittivity, the glassy state is not depending on the temperatures. It's value is about 37 units. At higher temperatures, when the material completely got into the smectic phase, the dielectric permittivity decreases again, which is in a complete agreement with the theoretical predictions.
Vertical line marked the phase transition temperature.
Most important results and conclusions are the following:. The conductivity of nanocomposites has an activating dependence in both glassy and smectic A phases. The conductivity of the nanocomposite along the cation-anion layers is in 2 orders of magnitude higher than across the cation-anion layers, confirming the structural anisotropy of the nanocomposite in the different phases of the materials.
Dielectric study on mixtures of ionic liquids
Electrons are the main charge carriers in the glassy phase. The increase of the NPs concentration brings additional free charge carriers or increases mobility of carriers. In the smectic phase, the increase of the nanoparticle concentration brings additional traps for the carriers, which travel in plane of the cation-anion layers. On the other hand, the nanoparticles deform the alkanoate chains and increase the mobility of the carriers traveling across the layers.
With the increase of the concentration of CdS and Au nanoparticles, the anisotropy of the conductivity increases for the smectic phase and decreases for the glassy phase. The temperature dependence of the dielectric permittivity of pure matrix CdC8 is very unusual and needs to be explored more. It is found that the dielectric permittivity increases at the temperatures close to the glass-liquid crystal phase transition. Such permittivity increase is not typical for ordinary glasses and needs additional investigations.
Feature of the synthesis nanoparticles in ionic crystal medium. Ukr Chem J. Green Industrial Applications of Ionic Liquids. London: Kluwer Academic Publishers; Electrical conductivity of lyotropic and thermotropic ionic liquid crystals consisting of metal alkanoates. Liq Cryst.
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Phys Chem Solid State. Monodispersity and ordering of semiconductor quantum dots synthesized in ionic liquid crystalline phase of cadmium alkanoates. J Chem Phys. Kovalchuk AV. Ukr Phys J. Download references. Correspondence to Gertruda Vasylivna Klimusheva. MTA synthesized the CdS nanoparticles in cadmium octanoate matrix. KGV carried out the preparation of the samples. ZD and KA made measurement of dielectric properties of ionic matrix cadmium octanoate with semiconductor and metal nanoparticles.
All authors read and approved the final manuscript. Reprints and Permissions. Search all SpringerOpen articles Search. Abstract Dielectric properties of ionic composites consisted of cadmium octanoate matrix and semiconductor or metal nanoparticles have been investigated. Background Researchers pay much attention to develop composite materials, as well as nanocomposites that exhibit new functional features.
Figure 1. Full size image. Figure 2. Figure 3. Figure 4. Figure 5. Table 1 Activation energy of conductivity on the concentration NPs in glassy phase of nanocomposites along and across cation - anion layers Full size table. Table 2 Activation energy of conductivity for smectic A phase on the concentration of NPs along and across cation - anion layers Full size table. Figure 6.