Authors Dukhin, St. ; Zimmermann, R. ; Werner, C.
Title Intrinsic Charge and Donnan potentials of grafted polyelectrolyte layers determined by surface onductivity data
Date 18.06.2004
Number 11674
Abstract In order to characterize grafted polyelectrolyte layers based on electrokinetic measurements a theory of the surface conductivity <i>K</i><sup>&#x3c3;</sup> was developed, starting from the model of thick polyelectrolyte layers with uniform segment distribution and dissociable groups with an unknown p<i>K</i> value. According to this model the inner part of the polyelectrolyte layer adjacent to the substrate is considered to be isopotential while the potential decay occurs in a zone near the solution side of the layer. A&#xa0;simple equation for the Donnan potential &#x3a8;<sub><i>D</i></sub> as a function of pH, p<i>K</i>, electrolyte concentration <i>C</i><sub>0</sub>, and volume charge density &#x3c1; was obtained. In the derived equation <i>K</i><sup>&#x3c3;</sup> is directly related to &#x3a8;<sub><i>D</i></sub>, while the other terms have less <br />influence on the magnitude of <i>K</i><sup>&#x3c3;</sup> and can be accounted for in a second approximation using &#x3a8;<sub><i>D</i></sub> as determined from the measured <i>K</i><sup>&#x3c3;</sup>. Evaluation of the suggested model indicates that <i>K</i><sup>&#x3c3;</sup> measurements provide an effective method to characterize polyelectrolyte layers by analyzing the dependence of &#x3a8;<sub><i>D</i></sub> on pH and <i>C</i><sub>0</sub>: The magnitude of <i>K</i><sup>&#x3c3;</sup> yields information about the surface charge at complete dissociation of the ionizable groups. The dependence of <i>K</i><sup>&#x3c3;</sup> on pH and <i>C</i><sub>0</sub> can be used for the determination of the p<i>K</i> value of the dissociating functions and the segment volume fraction of the polyelectrolyte can be estimated using the measured value of&#xa0;&#x3c1;.
Publisher Journal of Colloid and Interface Science
Citation Journal of Colloid and Interface Science 274 (2004) 309-318
Tags MBC_Electrosurface_Analysis

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