Complex electrosurface investigations of dispersed microphases

The structure of the electrical double layer (EDL) of colloidal systems is discussed. The methods of determination of the most important parameters of the EDL, i.e. the value of the surface-potential psi(0), the Stern-potential psi(delta) and the electrokinetic-potential delta, the surface charge density sigma(0), the electrokinetic charge sigma(zeta) as well as the specific surface conductance kappa(sigma) and Rel parameter are described. The application of the theory of non-linear electrosurface phenomena developed by Dukhin, Derjaguin and Shilov for calculation of the EDL parameters is discussed. The above data of the EDL characteristics for polystyrene and melamin-formaldehyde latices, suspensions of AgI, Sb2S3, Fe2O3, ZrO2, hydromica, palygorskyte, yeast cells as well as kerosene-in-water, ET grade lubricating oil technical emulsions in different electrolyte solutions are discussed. It has been shown that in the most of cases (with the exception of AgI solution) psi(0) or psi(delta) > zeta and sigma(0) >> sigma(zeta). It indicates the presence of a considerable free charge between the surface and slipping plane due to the formation of hydrodynamically immobile water layers on the surface in which the ions retain high mobility. The necessity of complex (integrated) electrosurface measurements for the description of the electrical double layer structure is stressed. A new kind of non-linear electrokinetic phenomena, namely the superfast electrophoresis is described. The phenomenon was predicted theoretically by Dukhin and Mishchuk and investigated experimentally in detail in the author's laboratory. It has been shown that the electrophoretic mobility of large (hundreds mu m) ion-type conducting particles like ion-exchanger grains/fibres or electron-type conducting particles like Al/Mg alloy, graphite and activated carbon in strong electric fields (100-1000 V/cm) exceeds the electrophoretic mobility values typical for non-conducting particles by 1-2 orders of magnitude. The mobility of such particles depends on the conductivity ratio between the particles and medium and strongly increases with the electric field gradient and the particle size. This is in contrast to classical electrophoresis. The superfast electrophoresis is due to the interaction of a strong electric field with the space charge near the surface of unipolar conducting particles. This space charge is induced by the strong external field because of the concentration polarisation. (C) 1998 Elsevier Science B.V.