Mechanisms of Surfactant Behavior at Different Interfaces

The adsorption phenomena discussed in the previous section utilized amphiphilic molecules of organic surfactants (predominantly synthetic ones). Here, it would be worthwhile to provide a brief description and classification of the most common types of organic surfactants [11-24], 

Synthetic surfactants represait important commodity products, with an annual production estimated at tens of millions of tons. While most of commercially available surfactants have been in production for years, new surfactant molecules, frequently targeting specialized applications, continue to appear. 

According to their physical-chemical nature, the surfactants can be subdivided into ionic (about 70% of all surfactants manufactured) and nonionic. In nonionic surfactants, the polar part mainly consists of multiple ethylene oxide units, -(CH2CH20) - while ionic surfactants can be subdivided into three large classes based on the charge of their polar group, that is, anionic, cationic, and zwitterionic (amphoteric) surfactants. 

In anionic surfactants, the carrier of surface activity, that is, the hydrocarbon chain, is a part of an anion having a negative charge. A well-known example of such surfactants are soaps, which are the alkali or ammonium salts of carbonic adds, for example, C H2 +iCOO Na The hydrocarbon chains of such soaps typically contain 12-18 carbon atoms. 

The excellent environmental properties of natural soaps come with a serious drawback weakly ionizable carboxylic groups do not show good solubility in hard water and in acidic medium, while the main commercial source for manufacturing these surfactants is livestock fat. 

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