COMPLEX ELECTROSURFACE INVESTIGATIONS OF DISPERSED MICROPHASES

The structure of the electrical double layer (EDL) of colloidal system s is discussed. The methods of determination of the most important par ameters of the EDL, i.e. the value of the surface-potential psi(0), th e Stern-potential psi(delta) and the electrokinetic-potential delta, t he surface charge density sigma(0), the electrokinetic charge sigma(ze ta) as well as the specific surface conductance kappa(sigma) and Rel p arameter are described. The application of the theory of non-linear el ectrosurface phenomena developed by Dukhin, Derjaguin and Shilov for c alculation of the EDL parameters is discussed. The above data of the E DL characteristics for polystyrene and melamin-formaldehyde latices, s uspensions 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 be en 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 indicate s the presence of a considerable free charge between the surface and s lipping plane due to the formation of hydrodynamically immobile water layers on the surface in which the ions retain high mobility. The nece ssity of complex (integrated) electrosurface measurements for the desc ription of the electrical double layer structure is stressed. A new ki nd of non-linear electrokinetic phenomena, namely the superfast electr ophoresis is described. The phenomenon was predicted theoretically by Dukhin and Mishchuk and investigated experimentally in detail in the a uthor's laboratory. It has been shown that the electrophoretic mobilit y of large (hundreds mu m) ion-type conducting particles like ion-exch anger grains/fibres or electron-type conducting particles like Al/Mg a lloy, graphite and activated carbon in strong electric fields (100-100 0 V/cm) exceeds the electrophoretic mobility values typical for non-co nducting particles by 1-2 orders of magnitude. The mobility of such pa rticles depends on the conductivity ratio between the particles and me dium and strongly increases with the electric field gradient and the p article size. This is in contrast to classical electrophoresis. The su perfast electrophoresis is due to the interaction of a strong electric field with the space charge near the surface of unipolar conducting p articles. This space charge is induced by the strong external field be cause of the concentration polarisation. (C) 1998 Elsevier Science B.V .