Double layer surface charge

Typically, the zeta potentials for latex or pigment particles are measured at different pH values. The zeta potential and hence the magnitude of the electric double-layer surface charge vary with the pH of the aqueous phase. The point at which the net charge is zero is termed the isoelectric point. 

This produces a double layer of charge, one localized on the surface of the plane and the other developed in a diffuse region extending into solution. 

On the electrode side of the double layer the excess charges are concentrated in the plane of the surface of the electronic conductor. On the electrolyte side of the double layer the charge distribution is quite complex. The potential drop occurs over several atomic dimensions and depends on the specific reactivity and atomic stmcture of the electrode surface and the electrolyte composition. The electrical double layer strongly influences the rate and pathway of electrode reactions. The reader is referred to several excellent discussions of the electrical double layer at the electrode—solution interface (26-28). 

Beyond the Stern layer, the remaining z counterions exist in solution. These ions experience two kinds of force an electrostatic attraction drawing them toward the micelle and thermal jostling, which tends to disperse them. The equilibrium resultant of these opposing forces is a diffuse ion atmosphere, the second half of a double layer of charge at the surface of the colloid. Chapter 11 provides a more detailed look at the diffuse part of the double layer. 

This chapter focuses on some of the basic theories of electrical double layers near charged surfaces and develops the expressions for interaction energies when two electrical double layers overlap ( interact ) with each other. 

In the case of a capacitor—taken here as a prototype of a double layer—the charges are not isolated. Instead, the lines of force emanating from one charged surface terminate at an opposite charge on the other plate of the capacitor. Figure 11.3a represents such a situation when the plates are separated by a vacuum. Suppose a plate of area A carries q charges then we define the charge density o as... 

DME, measured as drop time- or surface tension-potential curve, and a simplified model of the double layer, (b) Charging current-potential curve. 

The electrolyte double layer surface tension, charge density, and capacity... 

It is generally accepted that the electrical double layer around charged oxide surfaces consists of two parts [22] ... 

In colloid science we are particularly interested in the ionic atmosphere which is developed around a charged colloid particle, rather than around a single ion. In this context it is usual to call this ionic atmosphere an electrical double layer. The charge on the particle is distributed over its surface and is just balanced by the total charge in the double layer in which there is an excess of oppositely charged ions (counter-ions) (Figure 3.4). 

---