Carboxylic acids membranes

Ion clusters are commonly observed in the ionized forms of the perfluorinated membranes. The size of the clusters appears to be larger for sulfonate than for carboxylate membranes." " The size increases in the order Na, and Cs" and decreases with increasing number of functional groups per chain and with increasing temperature.As in the case of ethylene ionomers, the perfluorinated carboxylic acid membranes do not form ion clusters, at least in the dry state." The electrostatic interaction may be too weak to form ionic clusters. These observations are expected according to the Eisenberg theory (see Section II.2). 

The perfluorinated carboxylic acid membrane exhibits a higher resistance than Nafion membranes in SPE water electrolyzers. This is primarily due to small membrane swelling and slight dissociation of the carboxylic acid group in water or acid electrolyte with a pH <... 

After intensive research and development work, Asahi Chemical filed the basic patents of fluorinated carboxylic acid membrane and carboxylic and sulfonic acid membrane and the related electrolysis processes in 1974 (1 - 8). 

Figure 4.5 Change in transport number of a perfluorocarbon carboxylic acid membrane with concentration of sodium hydroxide. Transport number was measured from NaOH(m/)/Membrane/NaOH(m2). m2/m, = 1.0—1.5 mav — (mi + m2)/2. Transport number was calculated from membrane potential (EMF).

Many other similar applications have been reported such as the electrochemical determination of electroinactive cationic medicines,313 determination of urea,314 uric acid,315 and application to glucose biosensors to decrease interference of ascorbate, urate, and acetaminophen.316 Enzyme immobilized membranes are also sensing membranes, e.g. urea responsive membranes, poly(carboxylic acid) membranes in which urease is immobilized,317 fructose responsive membranes, and polyion complex membranes in which fructose dehydrogenase is immobilized.318 Such applications will expand further in the future and contribute to human life. 

The carboxylic acid membrane behaves differently [51], as the maximum appears at 12% NaOH concentration and the conductivity then decreases with increasing NaOH strength (Fig. 4.8.13). This is attributed to the loss of the water in the membrane and hence, decreased ionic mobility. These factors arise from the strong interactions between the fixed ions in the membrane and the counter ions. 

The membrane conductivity data used in the present calculation are those for a carboxylic acid membrane [97-99], as the overall conductivity of a composite membrane is dictated by the carboxylic layer. Diffusion coefficient data for chloride and chlorate ions across the commercial composite membranes are not available. Hence, an average of the diffusion coefficient data for the chloride ion for carboxylic acid membranes [100,101] was used, assuming the same temperature dependence as that of membrane conductivity. The diffusion coefficient of the chlorate ion was assumed to be the same as that of the chloride ion. Variations in Dq- and k with anolyte concentration, under commercial operating conditions, were reported [102] to be weak, and hence, these dependencies were not considered here. 

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