95 Electrical Phenomena at Interfaces and Biointerfaces: Fundamentals and Applications in Nano-, Bio-, and Environmental Sciences, First Edition. Edited by Hiroyuki Ohshima. © 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc. 7 SURFACE CONDUCTIVITY Stanislav S. Dukhin, Ralf Zimmermann, and Carsten Werner 7.1 INTRODUCTION The concept of specific surface conductivity was developed by considering charge transfer along almost flat double layers of cylindrical capillaries. It retains its meaning for dispersed particles, although the theory becomes more complicated. If an electric field is applied to a particle dispersion or a liquid-filled capil- lary system, two transport phenomena can be observed: the transport of matter (electroosmosis and electrophoresis) and the transport of charge (the exces- sive electric current due to presence of excess ions in the interfacial region, i.e., surface conduction). Both phenomena are closely related to the formation of electrical double layers and can be used to characterize the interfacial charge by two independent parameters: zeta potential, ζ, and surface conduc- tivity, K σ . The transport of matter and the transport of charge are coupled in a simple manner in the case of straight capillaries, while the coupling is rather complicated in the case of curved particle surfaces. In the latter case, double- layer deformation (polarization) has to be taken into account. For this reason, double-layer characterization by both ζ and K σ was first established for locally almost flat double layers of cylindrical capillaries. Afterward, research was performed mainly in two directions: 1. Development of Theories for Double-Layer Polarization and Nonequilib- rium Electrosurface Phenomena. The theoretical efforts were combined