Ionic conductivity organic crystals

Although a number of salts having organic chains have been synthesized to date, only a few salts were obtained as liquid or glass. In the case of the polyether/salt hybrid, the crystalline phase of both the salt and polyether disappear under appropriate conditions (Figure 22.2). The Polyether moiety in the polyether/salt hybrid is assumed to inhibit the crystallization of the salts by its flexible segmental motion. Since polyethers help dissociate the bound salt through their ion-dipole interactions, the polyether/salt hybrid inherently shows ionic conductivity. 

A further interesting effect discovered in our laboratories is that the addition of low levels of a second component, or dopant ion, can lead to significant increases in the ionic conductivity [6, 30, 31]. Typically these dopant species, for example, Li, OH , and H" ", are much smaller than the organic ions of the matrix, and since the relaxation times characterizing the motion of these ions are more rapid than those of the bulk matrix itself, these materials may represent a new class of fast ion conductor. The dopant ion effect can be used to design materials for specific applications, for example, Li+ for lithium batteries and H /OH for fuel cells or other specific sensor applications. Finally, we have recently discovered that this dopant effect can also be apphed to molecular plastic crystals such as succinonitrile [32]. Such materials have the added advantage that the ionic conductivity is purely a result of the dopant ions and not of the solvent matrix itself. 

In this chapter we have described the mesomorphic behavior and ionic conductivities of ionic liquid-based liquid crystalline materials. These ion-active anisotropic materials have great potentials for applications not only as electrolytes that anisotropically transport ions at the nanometer scale but also as ordered solvents for reactions. Ionic liquid crystals have also been studied for uses as diverse as nonliner optoelectronic materials [61, 62], photoluminescent materials [78], structuredirecting reagents for mesoporous materials [79, 80] and ordered solvents for organic reactions [47, 81]. Approaches to self-organization of ionic liquids may open a new avenue in the field of material science and supramolecular chemistry. 

There are different mechanisms of conductivity in organic compounds including liquid crystals. The most universal mechanism is ionic conduction. No matter how rigorously the material is purified, there always exist some ionic impurities. Under applied electric field these ions will migrate to the corresponding electrodes and contribute to the current. This current is characteristic of exponential increase with increasing temperature. One needs to pay attention to decipher the contribution of ionic conductance if the overall conductance of the sample is small. 

The scintillation process in inorganic scintillators differs from that in organic scintillators. Consider the structure of an ionic crystal, as shown in Figure 18.19. When an energetic electron passes through the crystal, it may raise valence electrons from the valence band to the conduction band. The electron vacancy in the valence... 

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