1 IONIC LIQUIDS 5 Per definition an ionic liquid will consist of ions capable

1 ionic liquids 5 per definition an ionic liquid will

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1.1. IONIC LIQUIDS 5 Per definition, an ionic liquid will consist of ions, capable of transporting charges and all ionic liquids are thus conductive with the ions acting as charge carriers. The degree of conductivity depends, as usual, on the viscosity of the ionic liquid and is thus highly dependent on temperature. The wide variation of the physicochemical properties of ionic liquids and the ease with which the design of the ionic liquid can be changed gave ionic liquids the name designer solvents in the latter part of the 1990s. Whilst this is true in theory, reality paints a different picture. Due to the vast amount of possible ionic liquids, basically any combination of properties can be incorporated into an ionic liquid. This does however require the painstaking trial and error process of synthesis and investigation until a suitable anion / cation combination can be found. As only about 1500 simple ionic liquids have been investigated to date there are still a lot of unknowns. In practice the industry currently chooses an ionic liquid that is close enough to the sought properties when designing a new process. With time the available material matrix will increase and will give more credence to the name designer solvents . Generally speaking, ionic liquids are seen as polar solvents due to the fact that they consist of ions. Ionic liquids can, however, dissolve both polar and non-polar solutes. The main factor that determines the ability of a solvent to dissolve a solute is the polarity of the solvent. Solvent polarity is not an easily determinable factor; it is actually often defined as the overall solvation capability of the solvent, that is to say, the ability for solvent molecules (or ions) to associate with solute molecules (or ions). In ionic liquids solvation can occur due to ion-ion interaction, dipole interaction, van der Waals forces as well as π - π interactions. One way to measure relative solvent polarity is through measuring the dielectric constant of the solvent. In general, liquids consisting of non-polar molecules have low dielectric constant whilst polar molecules lead to high dielectric constant. Measuring the polarity directly requires a non-conducting medium and as such one needs to employ alternate methods for measuring the dielectric constant indirectly. One such method was reported by Reichardt [ 20 ] who set the polarity of tetramethylsilane at 0.00 and the polarity of water at 1.00. On that scale ionic liquids were reported to have a polarity ranging from 0.35 to 1.10 with imidazolium based ionic liquids having polarities between 0.50 and 0.75, similar to that of ethanol. A good solvent has a high degree of solubility for the solute of interest and a high immiscibility for any byproducts and impurities. One interesting feature of ionic liquids is the wide range of possible solubilities and miscibilities that are available by changing between different ionic liquids. They can for instance dissolve both ionic and non-ionic species. The ability to dissolve a material in an ionic liquid depends mainly on two factors, the polarity of the ions and the possible degrees of coordination.
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