Anisotropic ionic conductivity

Finally, we consider the method for anisotropic ionic conductivity. Anisotropic ionic conductivity is a phenomenon that appears in a sample undergoing liquid crystalline phase or micro phase separation. In the nanotechnology field such samples are expected to yield important materials because they can raise the value of ion conduction. To measure the anisotropic ionic conductivity, one has to design a special cell. Figure 6.5 shows an example of a cell shaped Uke a comb [8]. In the comb-shaped cell, the ionic conductivity is measured between two teeth of the comb. As the liquid crystalline molecules orient perpendicularly on the glass substrate, the ionic conductivity is obtained along with the minor axis. The important task is to prepare the specific phase homogeneously in the measurement cell. The details will soon be presented in published papers. 

ANISOTROPIC IONIC CONDUCTIVITIES OF IONIC LIQUID CRYSTALS... 

Anisotropic ionic conductivities were measured by an alternating current impedance method [66, 67] for the samples forming oriented monodomains in two types of cells shown in Figure 25.10. The comb-shaped gold electrodes with thickness of... 

Figure 25.11 Anisotropic ionic conductivities of the complexes composed of equimolar amounts of mesogenic compounds 13,14 and ionic liquid 16 as a function of temperature ( ) parallel and (M) perpendicular to the smectic layer for the material based on 13 (O) parallel and (n) perpendicular to the smectic layer for the material based on 14.

Anisotropic ionic conductivities were also observed for nanostructured 2D films consisting of polymer 12 [28]. The conductivities parallel to the layer are... 

Figure 12.22. Schematic illustration of anisotropic ionic conduction in nanochannels with nanotemplates of azo LCBC films. The complexes PEO+UCF3SO3 were prepared at low-, medium-, and high salt concentration. Source Reproduced from Li et al., 2007a.

Spry, R.J., Alexander, M.D., Jr., Bai, S.J., Dang, T.D., Price, GJi., Dean, DJI., Kumar, B., Solomon, J.S., Arnold, F.E. (1997) Anisotropic ionic conductivity of lithium-doped sulfona.tedPBl. Journal of Polymer Science Part B Polymer Physics, 35,2925-2933. 

Liquid crystalline ionic liquids can be used as low dimensional ion conductors [6, 8, 26-29]. For this purpose the formation of oriented monodomains in the macroscopic scale is important because the boundary in the randomly oriented polydomains disturbs high and anisotropic ion conduction. 

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. 

Ionic conductivity in /3- or /3"-aluminas is anisotropic, because it takes place along the planes sandwiched between... 

The conducting ions, such as Na, populate the planes between the spinel blocks. For optimum two-dimensional ion conduction in these planes, it is preferable that not all the available sites be occupied by the mobile cations. As the temperatures increases, the mobile ions in these conducting planes become disordered and occupy positions at random. The ionic mobility of the Na in these planes is higher in the /J structure than it is in the / " structure because of the particular configuration of the bridging oxygen ions that act as obstacles to ionic motion within the plane. Na ion conduction is anisotropic and two-dimensional within these conduction planes for both the p and structures. No ionic conduction exists in a direction perpendicular to the conduction plane. 

These materials are extranely attractive for their optical and electrical properties. They have a high intrinsic ionic conductivity, which varies exponentially with temperature and is also anisotropic due to their bi-layer spatial structure [64]. For example, the lyotropic metal alkanoate potassium caproate showed a higher electrical conductivity in the smectic phase than in isotropic solutions. Since they are much less solvated within the layered structure of the smectic phase than in dilute... 

For organic materials, electronic and ionic conduction are important topics [1]. Liquid-crystalline (LC) polymers are good candidates for materials that transport ions and electrons because their ordered nanostructures are expected to induce anisotropic and efficient conduction [2-10]. However, limited numbers of examples have been reported for electron- and ion-active LC polymers, compared to crystalline and amorphous polymers [3-10]. 

A new concept for enhancing the conductivities for materials based on PEOs and ionic liquids was the introduction of ordered LC nanostructures [4,5,44-56]. In PEO materials, lithium cations are tightly coordinated with the PEO chains. The ions are conducted in isotropic matrices by 3D migration processes. Also, ionic liquids themselves, and the ions dissolved in ionic liquids, move randomly in the isotropic liquid media. If the polyether and ionic moieties that function as ion-conductive parts are organized into LC nanostructures, efficient ion transportation and anisotropic ion conduction are expected by the formation of low-dimensional ion-conductive paths. 

The introduction of macroscopically oriented nanostructures is an essential approach for low-dimensional ion conduction, because the boundaries between the domains oriented randomly disturbs anisotropic ion conduction. However, as mentioned above, it was difficult to produce macroscopically aligned thin films with a low density of defects and domain boundaries, and therefore anisotropy in ionic conductivity has not been observed clearly. 

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