Dynamic electrophoretic mobility in concentrated dispersed systems. Cell model

Electroacoustic characterization of concentrated dispersed systems requires an adequate theory of dynamic electrophoretic mobility which takes into ac count particle-particle interaction. The concept of the "cell model" provid es convenient and comprehensive means for creating this theory. There are t wo different versions of the electrokinetic cell model. The first one was i ntroduced by Levine and Neale, the second one by Shilov and Zharkikh. The L evine-Neale cell model gives a large discrepancy with experimental data as it was shown by O'Brien and Hunter. We suggest several reasons indicating t hat the Shilov-Zharkikh cell model is more adequate than the Levine-Neale o ne. First of all, it gives transition to the Smolichowski law for electroos mosis which is valid for concentrated systems. The Shilov-Zharkikh. cell mo del yields a symmetrical Onsager relationship between kinetic coefficients as well as the Maxwell-Vagner law for electric conductivity. In addition, t he Shilov-Zharkikh cell model predicts much stronger volume fraction depend ence of dynamic electrophoretic mobility. Such strong dependence correspond s to O'Brien-Hunter experimental data which could not be explained by the L evine-Neale cell model. We developed two versions of the theory using diffe rent constrains. The first version is valid only at low frequency, but it t akes into account surface conductivity. The second version neglects surface conductivity. At the same time this second version takes into account iner tia effects which makes it valid at high frequencies. We do not address a q uestion of the appropriate frame of references for the dynamic electrophore tic mobility. All calculations are performed in the frame of references whi ch is associated with the liquid.