Molecular self-assembly and charge transfer phenomena in ionic liquid organic gels: Investigation of molecular and electrophoretic dynamics
Objectives
Ionic liquids in their high temperature manifestations (high temperature ionic liquids – HTILs: liquid oxides, silicates, salts) have been studied for a long time, using quite sophisticated methods, and much of their physics and chemistry is rather well understood. In contrast, room temperature ionic liquids (RTILs) are more novel and less well understood systems. The existence of the liquid phase below 100°C makes these materials very desirable in various applications, thus the interest in such kind of compounds is very high. Both classes of materials can be used to create composites, classified as functional materials which composition is based on low molecular weight organic gelators (LMOGs). The extensive research in field of LMOGs led to creation of a new class of materials which continuously finds new applications. One of the newest idea is to use these materials for creation of ionic gels which among others applications can serve as a new way of ionic liquid solidification process. To categorize a gelator as LMOG it’s mass have to be below 1000u. The materials, which are in the focus of this project, poses very interesting physical and chemical properties which can be controlled by external conditions. The cation of an RTIL is often a large organic ion, such as an imidazolium, a pyridinium or a quaternary ammonium ion and their derivatives. As anions, Clˉ, Brˉ , BF4ˉ, PF6ˉ or CF3SO3ˉ are popular choices. Figure 1 presents examples of cations and anions commonly used in ionic liquids.
Organic ionic gels (OIGs) are created by non-covalent self-assembly upon cooling down the mixture of a LMOG and solvent (HTIL, RTIL or their mixtures). As the final product of gelation process, we can obtain a transparent, thermally stable and reversible physical gel that can adapt to external boundaries (see figure 2). The properties of created OIGs are very often different from that of the individual components and depend also on the self-assembly process. The unique feature of LMOGs hitherto used which attracted considerable interest is that they can create different one-, two-, or three-dimensional networks of fiber-like aggregates that can entrap a large amount of liquid phase. The driving forces of gelation are cooperative, non-covalent interactions which can have diverse origin and can involve a complex local structure [9,10]. Examples of systems that can form organic ionic gels are imidazolium or pyridinium salts as RTILs and derivatives of a cyclo(dipeptide)s such as cyclo(L-β-2ethylhexylasparaginyl-L-phenylalanyl) as LMOG can be mentioned [11,12]. However, it is worth to notice that not all of the LMOGs can gel up ionic liquids.
OIGs can provide an alternative way of obtaining solid electrolytes and received special attention for theirs potential use in a variety of electrochemical devices such as batteries, fuel cells, energy storage and chemical sensors [13,14]. Solidification of ILs is a very expensive and complicated process whereas OIGs can be produced much easier and cheaper. With the gelation process well understood the properties of the created gel would also be easy to control.
The results of the project were disseminated as scientific publications, lectures and posters on scientific conferences, and invited lectures.