Water was originally inimical to ionic liquids (ILs) especially in the analysis of their detailed properties. Various data on the properties of ILs indicate that there are two ways to design ...functions of ionic liquids. The first is to change the structure of component ions, to provide "task-specific ILs". The second is to mix ILs with other components, such as other ILs, organic solvents or water. Mixing makes it easy to control the properties of the solution. In this strategy, water is now a very important partner. Below, we summarise our recent results on the properties of IL/water mixtures. Stable phase separation is an effective method in some separation processes. Conversely, a dynamic phase change between a homogeneous mixture and separation of phases is important in many fields. Analysis of the relation between phase behaviour and the hydration state of the component ions indicates that the pattern of phase separation is governed by the hydrophilicity of the ions. Sufficiently hydrophilic ions yielded ILs that are miscible with water, and hydrophobic ions gave stable phase separation with water. ILs composed of hydrophobic but hydrated ions undergo a dynamic phase change between a homogeneous mixture and separate phases according to temperature. ILs having more than seven water molecules per ion pair undergo this phase transition. These dynamic phase changes are considered, with some examples, and application is made to the separation of water-soluble proteins.
Polymerised ionic liquids (PILs) have unique properties such as low glass transition temperature (Tg) in spite of very high charge density. Due to these advanced points, PILs have been prepared and ...initially evaluated as ion conductive polymers. Progress of low-Tg polyelectrolytes has been previously demonstrated with polyethers having charged end(s) as a kind of PILs. Then, imidazolium-type ionic liquids (ILs) were polymerised after introducing vinyl groups onto the imidazolium cation rings. It is reasonable that the ionic conductivity of thus prepared PILs decreased due to elevation of Tg and decrease of the number of mobile small ions. Efforts were then paid to suppress drop of ionic conductivity after polymerisation. Variety of PILs has been improved to show excellent ionic conductivity, selective ion transport, and other properties. With the progress of functional ILs, some functions were also added to PILs which cannot be realised with ordinary charged polymers. In the present mini-review, we briefly introduce history of a variety of polymerised ILs and some applications of these PILs.
Display omitted
Some ionic liquids have been polymerized after introducing vinyl groups on the component ions. Thus obtained polymerized ionic liquids showed relatively low glass transition temperature and moderate ...ionic conductivity attributable to unique characteristics of the ionic liquids. The properties of the polymers such as glass transition temperature, decomposition temperature, ionic conductivity, etc, have been further improved through the design of corresponding monomers. It is important to consider a task‐sharing between component monomers, such as providing conductive path and carrier ion source for the design of conductive polymers for specific ions.
Phase separation between ionic liquids (ILs) and molecular liquids is of interest physico-chemically, and also has industrial relevance. IL/water mixtures are of great interest in many fields. Unlike ...static phase separation between IL and water, dynamic shifts of IL/water mixtures between a homogeneous mixture and separate phases have a wide variety of applications. The miscibility of ILs with water generally increases upon heating, and a few ILs undergo a lower critical solution temperature (LCST)-type phase transition with water in which the separated biphases become miscible upon cooling. As the phase transition is controlled by changing the temperature by a few degrees, the LCST-type phase response of IL/water mixtures makes it possible to use ILs as solvents in various energy-saving processes. Since many hydrophilic ILs do not undergo phase separation with water, we aim to determine the necessary conditions under which hydrophobic ILs undergo the phase transition. Based on physico-chemical analysis of many hydrophobic ILs that undergo a phase separation after mixing with water, we find there is a particular range of "hydrophilicity" of these hydrophobic ILs within which the LCST-type phase transition is possible. Accordingly, a hydrophilicity index (HI) of ILs is proposed, in terms of the number of water molecules in the separated IL phase. The HI value proves to be a good indicator of the phase behaviour of IL/water mixtures, as well as their phase transition temperature. Potential application of the LCST-type phase change to the selective extraction of water-soluble proteins is also summarised.
Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in ...applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.
PDF
