ABSTRACT
As a general rule, particles suspended in a polar liquid medium such as water show an electrical charge. This can be veried by applying an electric eld to such a suspension, which in most cases will cause a net displacement of the particles in a direction parallel to the eld. The presence of a charge of any sign on the particle surface requires, for an electrically neutral system, a charge of opposite sign and the same magnitude on the liquid phase side. In other words, the surface charge on the particle is counterbalanced by ions on the liquid phase. Thus, in general, there is an electrostatic contribution to the energies associated with processes taking place at the particle surface. Although we will postpone the analysis of the origin and nature of the surface charge until Chapter 5, here we will consider as an experimental fact the presence of charge and will study the electrostatic potential prole and the ion distribution resulting from that charge. We will also restrict ourselves to aqueous media, as this is the most common case, and certainly the one present in soils.
