Polyelectrolyte system

Glass—Ionomer Cement. The glass—ionomer polyelectrolyte system was developed primarily as a restorative for anterior teeth and erosion cavities a general cement a cavity liner and a base, pit, and fissure sealant (27,43—48). 

The preparation of molecular composites by electropolymeriza tion of heterocycles in solution with polyelectrolytes is an extremely versatile technique, and many polyelectrolyte systems have been studied. The advantages of this method include the use of aqueous systems for the polymerization. Also, the physical and mechanical properties of the overall composite depend on the properties of the polyelectrolyte, so material tailorabiUty is feasible by selection of a polyelectrolyte with desirable properties. 

Photoinduced Electron Transfer in Amphiphilic Polyelectrolyte Systems... 

This review article attempts to summarize and discuss recent developments in the studies of photoinduced electron transfer in functionalized polyelectrolyte systems. The rates of photoinduced forward and thermal back electron transfers are dramatically changed when photoactive chromophores are incorporated into polyelectrolytes by covalent bonding. The origins of such changes are discussed in terms of the interfacial electrostatic potential on the molecular surface of the polyelectrolyte as well as the microphase structure formed by amphiphilic polyelectrolytes. The promise of tailored amphiphilic polyelectrolytes for designing efficient photoinduced charge separation systems is afso discussed. 

Functionalized polyelectrolytes are promising candidates for photoinduced ET reaction systems. In recent years, much attention has been focused on modifying the photophysical and photochemical processes by use of polyelectrolyte systems, because dramatic effects are often brought about by the interfacial electrostatic potential and/or the existence of microphase structures in such systems [10, 11], A characteristic feature of polymers as reaction media, in general, lies in the potential that they make a wider variety of molecular designs possible than the conventional organized molecular assemblies such as surfactant micelles and vesicles. From a practical point of view, polymer systems have a potential advantage in that polymers per se can form film and may be assembled into a variety of devices and systems with ease. 

The modification of reaction rates by such a functionalized polyelectrolyte system was first made in 1959 by Ladenheim and Morawetz [23] in the Menshutkin... 

Until recent years only a relatively few studies had been reported on the amphiphilic polyelectrolytes. However, several years ago attention began to be directed to the microphase structure as a reaction medium that modifies photophysics and photochemistry [50 — 64], redox processes [65 — 67], and chemical reactions [68, 69]. Since then the number of reports on amphiphilic polyelectrolyte systems have increased sharply. 

Equations for the evaluation of formation constants of complexed ion species in cross-linked and linear polyelectrolyte systems. J. A. Marinsky, Ion Exch. Solvent Extr., 1973,4, 227-243 (18). 

Rg,6 is the radius of giration in the 6-state assumed to correspond in polyelectrolyte systems to the value extrapolated to infinite salt concentration. The relation of Benoit-Doty for high molecular weights gives ... 

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

Morishima, Y Photoinduced Electron Transfer in Amphiphilic Polyelectrolyte Systems. VoL 104, pp. 51-96. 

Hoagland, D.A., Arvanitidou E., and Welch C., Capillary Electrophoresis measurements of the free solution mobility for several model polyelectrolyte systems, Macromolecules, 32, 6180, 1999. 

The ideas I.M. Lifshitz suggested in his works were also used in developing a theory of another related phenomenon, namely, microphase separation in polyelectrolyte systems [55]. 

Mg has been studied in a polyelectrolyte system where the counterion is a phosphazene-bound sulphonate group. In this case the finite but low conductivity is due to Mg migration. A large increase in conductivity is noted when a bicyclic ligand, crypt [2.1.1.], is introduced (Hancock and Martell, 1988). Apparently, the cation-anion and cation-polymer interactions are reduced by complex formation, resulting in a more mobile cation, despite its larger effective radius. 

Coulombic, van der Waals, entropic and osmotic forces are coupled in a nontrivial way and give rise to important charge regulation in polyelectrolyte systems. The salt concentration is also an important factor to define the structure and thermodynamic properties of polyelectrolyte solutions. In weak polyelectrolytes the ionization equilibrium is also coupled to these interactions and thus the pKof ionizable groups depends on the organization of the interface and differs from that for the isolated molecule. 

Due to the presence of interactions, the apparent redox potential of a redox couple inside a polyelectrolyte film can differ from that of the isolated redox couple in solution (i.e. the standard formal redox potential) [121]. In other words, the free energy required to oxidize a mole of redox sites in the film differs from that needed in solution. One particular case is when these interations have an origin in the presence of immobile electrostatically charged groups in the polymer phase. Under such conditions, there is a potential difference between this phase and the solution (reference electrode in the electrolyte), knovm as the Donnan or membrane potential that contributes to the apparent potential of the redox couple. The presence of the Donnan potential in redox polyelectrolyte systems was demonstrated for the first time by Anson [24, 122]. Considering only this contribution to peak position, we can vwite ... 

As was mentioned before, charge compensation during oxidation in redox polyelectrolyte systems can be achieved by anion uptake or cation release. For example, for a PAH-Os/PVS-modified eledrode, we can write ... 

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