Capacitance salt concentration dependence

In sec. 3.6 it was shown that, to a first approximation, C does not depend on the salt concentration, whereas does. At salt concentrations of about 0.1 mol dm C becomes so large that C= C . Under these conditions any change in C upon adsorption of polymer must reflect the presence of train segments. The amount adsorbed in trains is then obtained by comparing the Stern capacitance in the absence (C °) and in the presence (C ) of adsorbed polymer, provided the capacitance for a surface fully covered with a monolayer of segments (denoted by C ) is known. Then... 

FIGURE 2.18 Dependence of capacitance on the salt concentration. (Reprinted from Journal of Power Sources, 196, Xu, C. J. et al., Charge storage mechanism of manganese dioxide for capacitor application Effect of the mild electrolytes containing alkaline and alkaline-earth metal cations, 7854-7859, Copyright 2011, with permission from Elsevier.)... 

Only the Faradaic current resulting from the electrolysis process varies linearly with c the capacitive current generally tends to depend on the total salt concentration which is dominated by the supporting electrolyte. Therefore the overall peak current, fpf, is a linear function of c but is not zero in the absence of a redox-active species since a capacitive current is stiU present. When interpreting experimental data it is important to carefidly choose a baseline from which the Faradaic current may be measured and hence allow analytically useful data to be obtained. 

Therefore some indirect methods have been worked out to determine the value of ff=0.154,259 In particular (1) salting out of organic compounds from a surface-inactive electrolyte solution, (2) F"" for 1-pentanol or other organic compounds with a high attractive interaction constant a, and (3) dependence of the capacitance minimum on thiourea concentration. It should be noted that indirect estimates based on TU adsorption give... 

The electrical properties of polyelectrolyte complexes are more closely related to those of biologically produced solids. The extremely high relative dielectric constants at low frequencies and the dispersion properties of salt-containing polyelectrolyte complexes have not been reported for other synthetic polymers. Neutral polyelectrolyte complexes immersed in dilute salt solution undergo marked changes in alternating current capacitance and resistance upon small variations in the electrolyte concentration. In addition, their frequency-dependence is governed by the nature of the microions. As shown in... 

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