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Thermoreversible Ion Gels Based on Ionic Liquids

出版	Universitat Politècnica de Catalunya. Escola Tècnica Superior d'Enginyeria Industrial de Barcelona, 2008 (Enginyeria Química), 2008
URL	http://books.google.com.hk/books?id=ZrImywEACAAJ&hl=&source=gbs_api

註釋Ionic liquids (ILs), substances composed entirely of ions, which are in a liquid state at temperatures below 100 °C, appeared in recent years as novel substances, and are used in different industrial processes. Unlike conventional substances, the properties of ILs (e.g., viscosity, solubility, ionic conductivity, melting point, etc.) can be tuned in wide intervals by varying the composition of their ions. Furthermore, ILs are considered as stable and "environmentally friendly" compounds due to their negligible vapor pressures, negligible flammability and liquid state in a broad temperature range. ILs have extensively been utilized in the preparation of ion gels, a new class of solid state electrolytes with high ionic conductivities, which have found applications in chemical sensors, gas separation membranes, power sources, lithium batteries, dye-sensitized solar cells, electromechanical actuators, organic thin film transistors, capacitors, polymer light-emitting electrochemical cells, and other electrochemical devices. Quasi-solidification of ionic liquids by chemical or physical gelation is one of the most important aspects in the design of the applications of ion gels; this aspect essentially aims at overcoming the conventional disadvantages of liquid electrolytes (i.e., leakage, flammability, toxicity and stability). The present work addresses a new, convenient, and inexpensive method to achieve the gelation of certain ILs in order to obtain ion gels of outstanding physical properties (i.e., high ionic conductivities, remarkable mechanical properties, and the possibility to tune the gelation temperature of these ion gels). Thus, this project describes about the aqueous gelation of quaternary ammonium based ILs. The obtained ion gels have shown values of storage modulus above 105 Pa at room temperature conditions and ionic conductivities above 60 mS cm-1, which exceed the values for these properties for most of polymer based ion gels reported so far. Moreover, the melting point transitions of the ion gels can be tuned from -60 oC to 53 oC by varying the concentration of water and salt in the material. In addition, the preparation method proposed in this contribution avoids completely the use of potentially harmful organic solvents. These findings, next to the fact that the proposed method is very simple and inexpensive, when compared to other approaches, turn these new ion gels as good candidates to improve or develop new applications.