Effects of Surfactants on Wetting Processes

If significant surfactant adsorption occurs at the oil-solid interface, displacement of the oil by aqueous solution will be hindered. 

If little or no adsorption occurs at the solid-water interface, detergency will be adversely affected. 

The most effective surfactants will be those which lower Si2 the most, while not coming into conflict with statements 1 and 2. 

In other words, the best surfactant from the point of view of detergency should be one that adsorbs well at the soUd-water and water-oil interfaces, but not at all at the solid-oil interface. 

Having mentioned several times the use of surfactant solutions in wetting studies, we now consider specifically some of the effects their presence can have on contact angles and wetting. The action of surfactants derives from their adsorption at the various interfaces and the resultant modification of interfacial tensions. In terms of the Gibbs equation, the relationship between the specific adsorption of a solute, G, and surface tension is given by 

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