Electrolyte chains

Exceptions occur in the case of polyelectrolytes where a, in the absence of added salts, may approach two. The difference arises here because at infinite dilution the charges cause the poly electrolyte chain to become nearly fully extended. 

Therefore we expect Df, identified as the fast diffusion coefficient measured in dynamic light-scattering experiments, in infinitely dilute polyelectrolyte solutions to be very high at low salt concentrations and to decrease to self-diffusion coefficient D KRg 1) as the salt concentration is increased. The above result for KRg 1 limit is analogous to the Nernst-Hartley equation reported in Ref. 33. The theory described here accounts for stmctural correlations inside poly electrolyte chains. 

Maeda M, Kumano A, TirteU DA. H -I- -Induced release of contents of phosphatidylcholine vesicles bearing surface-bound poly-electrolyte chains. J Am Chem Soc 1988 110 7455-7459. 

Takagi, S. and Yoshikawa, K. (1999) Stepwise collapse of poly electrolyte chains entrapped in a finite space as predicted by theoretical considerations. Langmuir, 15, 4143 1146. 

The last term in the free energy describes the correlation between the ion pairs on the poly electrolyte chain. One term in this free energy, /v>,i, depicts correlations between the ion pairs, while the remaining term, F(, i, accounts for... 

Finally, it is interesting to note that the value of a for the poly-(metaphosphate) chain [Strauss and Wineman (241 )] has the same order of magnitude as those of non-electrolyte chains with substituents of comparable size. Under the observed theta-solvent conditions (0.415 M aqueous NaBr), the screened long range electrostatic interactions are just balanced by the various other contributions to the excluded volume effect, but there is no reason to expect a simultaneous obliteration of short-range electrostatic effects1. 

Sensors may also use multiple electrolytes (referredto as electrolyte chains), and two examples of these are shown in Figure 13.Id and e. In both examples, a Na2SO4 auxiliary electrode is used with a sodium ion conductor so that the sensing electrode reaction is given by Equation (13.5). The difference between the two cases is that, in Figure 13.Id, the sodium ion conductor is used with another cation (strontium) conductor, whereas in Figure 13.le the sodium ion conductor is used with an anion (oxygen) conductor. In both cases, an equilibrium reaction is required to relate the... 

The equilibration between the two electrolytes can sometimes require an additional phase, some specific examples of which will be discussed later in the chapter. One advantage of using an electrolyte chain is that the reference electrode reaction need not be the same as the sensing electrode reaction, which in turn expands the choice of potential reference electrodes. In addition, the electrolyte that provides the best performance may not be commercially available or easy to fabricate. I n such cases, a commonly available, easily fabricated or low-cost electrolyte can be used for the primary structure, and a coating of the better-performing electrolyte applied to the surface. 

Figure 13.7 Outputs of CO2 and SO2 sensors with NASICON/p alumina electrolyte chains [88-91],...

As mentioned above (and shown in Figure 13.9c), when electrolyte chains are used the electrolyte in contact with the reference electrolyte can be different from that used for the sensing electrode, which provides flexibility in the design of the reference electrode material. 

Figure 13.9 Schematic of reference electrode, (a) Gas-phase reference (b) Solid-state reference (c) Reference with electrolyte chain.

A similar approach is used in CO2 gas sensors based on electrolyte chains of YSZ and cation conductors. Specifically, YSZ has been used with magnesium- [223], aluminum- [96, 105, 224, 225], or scandium- [225-227] conducting electrolytes and Li2CO3-containing electrodes. The sensitivity to CO2 is attributed to the dissolution of lithium in the electrolyte rather than to the formation of a new carbonate phase. 

Species listed above (sodium salts) have been characterized in water and/or aqueous IMaCl solution in terms of Na counterion activity coefficient, heat of dilution, and heat of Cu ions binding. These experiments are part of a systematic investigation on the relationship between "charge-density" along poly-electrolyte chains and (metal] ion-binding, comparing experimental evidence with existing theories (J, 3). ... 

Cremer, M., Origin of electromotor properties of tissues, and instructional contribution for polyphasic electrolyte chains. Zeitschriftftlr Biol 1906,47, 562-608. 

The successfiil synthesis of a transparent soHd polymer electrolyte (SPE) based on PEO and alkoxysilanes has been reported (41). The material possessed good mechanical properties and high electrical conductivity (around 1.8 x 10 S/cm at 25°C) dependent on the organic—inorganic ratio and PEO chain length. 

Possibility of changing the properties of micellar phases by electrolyte inclusions was shown. Under this condition, in the systems with manifestation of complexes formation between the cationic compound of the electrolyte and the polyoxyethylene chain of the surfactant, increase of the hydrophilic properties of micellar phases was observed. The electrolytes that do not have affinity to the surfactant s molecule practically do not influence the liophily of the nonionic surfactant-rich phases. 

It is interesting to note that the amino acid side chains may be either neutral as in valine, acidic as in glutamic acid or basic as in lysine. The presence of both acidic and basic side chains leads to proteins such as casein acting as amphoteric electrolytes and their physical behaviour will depend on the pH of the environment in which the molecules exist. This is indicated by Figure 30.2, showing a simplified protein molecule with just one acidic and one basic side group. 

The reaction is likely to proceed by a radical-chain mechanism, involving intermediate formation of carboxyl radicals, as in the related Kolbe electrolytic synthesis. Initially the bromine reacts with the silver carboxylate 1 to give an acyl hypobromite species 3 together with insoluble silver bromide, which precipitates from the reaction mixture. The unstable acyl hypobromite decomposes by homolytic cleavage of the O-Br bond, to give a bromo radical and the carboxyl radical 4. The latter decomposes further to carbon dioxide and the alkyl radical 5, which subsequently reacts with hypobromite 3 to yield the alkyl bromide 2 and the new carboxyl radical 4Z... 

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