Supramolecular electrolyte

Some recent examples including uses as super hydrophobic surfaces [142], medical composites of spun fibers, generating scaffolds for cell attachment [138], thermoplastic elastomers [139], as a supramolecular electrolyte in a dye-sensitized solar cell [190], as a method to align polymer chains [191], or as supramolecular polymer composites [192] have been discussed previously. Still there is ample space to be explored and there definitely will be many more patents and applications in this field. 

Therefore, thermodynamics plays a fundamental role in supramolecular chemistry. However, thermodynamics is rigorous and as such, a great deal of ancillary information is required prior to the formulation of an equation representative of the process taking place in solution, such as, the composition of the complex and the nature of the speciation in solution. For the latter and when electrolytes are involved, knowledge of the ion-pair formation of the free and complex salts in the appropriate solvent is required particularly in non-aqueous solvents. This information would allow the establishment of the concentrations at which particular ions are the predominant species in solution. Similar considerations must be taken into account when neutral receptors are involved, given that in dipolar aprotic or inert solvents, monomeric species are not always predominant in solution. In addition, awareness of the scope and limitations of the methodology used for the derivation of thermodynamic data for the complexation process is needed and this aspect has been addressed elsewhere [18]. 

Figure 3.9 illustrates the electrochemical and mass transport events that can occur at an electrode modified with a interfacial supramolecular assembly [9]. For monolayers in contact with a supporting electrolyte, the principal process is heterogeneous electron transfer across the electrode/monolayer interface. However, as discussed later in Chapter 5, thin films of polymers [10] represent an important class of interfacial supramolecular assembly (ISA) in which the properties of the redox center are affected by the physico-chemical properties of the polymer backbone. To address the properties of these thin films, mass transfer and reaction kinetics have to be considered. In this section, the properties of an ideally responding ISA are considered. 

The interfacial capacitance can also provide a significant insight into the permeability of interfacial supramolecular assemblies. While information of this kind complements studies using redox-active probes in solution, it also provides information on a significantly shorter length scale, i.e. that of electrolyte ions and solvent molecules. For example, for dense, defect-free monolayers, the limiting capacitance is very much lower (5-10 pF cm-2) than that found for an unmodified interface (20-60 pF cm 2). 

In the following, factors external to the actual interfacial supramolecular assembly, which are capable of modifying the photoinduced electron injection process, are considered. This discussion will concentrate on how the rate of charge injection can be manipulated by changing the composition of the electrolyte and by changing the external potential applied to the semiconductor film. 

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. 

Such specifics of interaction between dipoles of H O, cations and anions mostly determine the structure of water solution. The simplest idea of it is provided by the statistical theory of diluted solutions of strong electrolytes proposed by Peter Joseph Debye (1884-1966) and Erich Armand Hiickel (1896-1980) in 1923. Under this theory ions are treated as rigid non-polarizable spheres separated by a uniform medium with high value of the dielectric constant. At that, structure of the solution is function of distances dipoles H O and ions. Depending on it, it is customary to distinguish molecular and supramolecular structure. Molecular structure is determined by a direct effect of ions on the orientation and mobility of water dipoles and is manifested first of all by the formation of hydrates. Supramolecular structure is caused by undisturbed interaction of H O molecules between each other (Figure 1.2). 

Figure 5.13. Voltammetric response of a glassy carbon (A), 4-aminopyridine-electrode (B), and the supramolecular electrode (formed by packed Co(II) benzoporphyrins) (C) under N2 (continuous line) and CO2 (dashed line). Scan rate 0.05 V s . Electrolyte phosphate/biphosphate (pH 6.8 under N2, pH 5.2 under C02) buffered aqueous solution. Reprinted from Figure 4A (A), Figure 4B (B) and Figure 5(C) G. Ramirez, M. Lucero, A. Riquekne, M. Villagran, J. Costamagna, E. TroUund and M.J. Aguirre, A supramolecular Cobaltporph5Tin-modified electrode toward the electroreduction of CO2, Journal Coordination Chemistry, 57 (2004) 249-255. With permission of Taylor and Francis (http //www.tandf.co.uk/journal).

Fig. 5.1 a For compact microcubic structure formation, the PB-CD nanoparticles undergo nucleation process within the LbL flask conducting to the formation of microcrystals that support a mesoscale self-assembly process and a final supramolecular conversion to compact microcubic structures, b Cyclic voltammograms (CVs) for self-assembly PAH/PB-CD multilayers onto ITO electrode containing three bilayers at various scan rate 10-200 mV s Electrolyte KCl— 0.2 mol T = 25 °C. Adapted with permission from [30]... 

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