ABSTRACT
Any surface in contact with water acquires an electrical
charge. This may be due to ionization of superficial
functional groups or to adsorption of ions or ionic
molecules, such as ionic surfactants or polyelectrolytes.
As a consequence of this surface charge, an electrical
potential profile is built up in the aqueous phase at the
particle surface, as described by the so-called electric
double-layer theory (1-3). The amount of charge pre-
sent at the surface of either microscopic or macro-
scopic surfaces affects its electrostatic interactions with
neighboring particles or molecules. Hence, surface
charge is an important characteristic in any interaction
process, such as flocculation or coagulation of colloi-
dal particles, which in turn has an effect on phenomena
such as sedimentation or creaming, as well as on the
rheology of dispersions (4-6). Depending on the experimental technique used, the
properties of charged surfaces are expressed explicitly
as the surface charge density, 0, or implicitly as the electrokinetic or zeta-potential, . According to the Gouy-Chapman electric double-layer theory, both
properties are interrelated by means of the surface
potential 0 (1-3):
