Surface electrostatic charge, effect

The effect of surface electrostatic charge on a material on the attachment of the decay products of radon has been known since pioneering work on atomic structure by Rutherford. Extensive research into this area for the radon and thoron progeny has been conducted in this laboratory for environmental monitoring purposes. Several authors have reported on the effect of electrostatic charge on the collecting characteristics of copper for the radon progeny for exploration purposes (Card and Bell, 1979). 

In practice, the occurrence of steric effects in adsorption of simple ions is probably not common. Evidence for this lies in the fact that adsorption equations using single value/concentration independent mass action constants are frequently found to fit experimental adsorption data quite well. Also, since typical surface sites occupy an area of the order of 50-100 based on surface electrostatic charge measurements... 

Particularly in polar solvents, electrostatic charges usually have an important contribution to tire particle interactions. We will first discuss tire ion distribution near a single surface, and tlien tire effect on interactions between two colloidal particles. 

Thus, in the relatively simple case of oil in water emulsions, where a surface active agent such as a soap is used as the emulsifying agent, it is known that the soap adsorbed on the surface of the oil particles decreases the interfacial tension, thus stabilizing the emulsion. The adsorbed soap ions also give a net electrostatic charge to the dispersed oil droplets, serving to repel other oil droplets, with the net effect that flocculation is hindered (and stability is increased). It is even possible to measure the amount of adsorbed soap ions and to calculate the values of the surface potential. 

The limitations of the Kt approach stem in part from the fact that it makes no accounting of the number of sorbing sites on the sediment, treating them as if they are in excess supply. The approach allows a solute to sorb without limit, without being affected by the sorption of competing species. As well, the approach treats sorption as a simple process of attachment. It does not consider the possibility of hydrolysis at the interface between sediment and fluid, so it cannot account for the effects of pH. Nor does the approach consider electrostatic interactions between the surface and charged ions. 

---