APPLICATION AND DETERMINATION OF SURFACE-ACTIVE AGENTS
PART II: ANIONIC SURFACTANTS
Lawrence K. Wang, Associate Professor
Department of Mechanical Engineering
Stevens Institute of Technology
Hoboken, New Jersey 07030
Shinn-Fwu Kao, Graduate Student
Mu Hao Wang, Associate Professor
Jao-Fuan Kao, Professor and Chairman
Department of Environmental Engineering
National Cheng Kung University
Tainan, Taiwan, China
Andrea L. Loshin, Graduate
Department of Chemical and Environmental Engineering
Renssealer Polytechnic Institute
Troy, New York 12181
INTRODUCTION
Application of Anionic Surfactants
A surface active agent, or surfactant, is an organic molecule which contains both
hydrophilic and hydrophobic functional groups (the latter usually a very long carbon
skeleton). The hydrophobic end of the surfactants can combine with greasy dirt and
fats. These molecules lower the surface tension [ 1 ]   of the water, and the surfactant
can pull the dirt away from the body, leaving it clean, and will collect at the surface
or interface of the liquid and air. This dual nature of the molecule enables the surfactant to be an excellent cleansing agent.
There are three kinds of surfactants, as follows: non-ionic, cationic, and anionic.
Non-ionic types are primarily used as detergents. Cationic surfactants are useful in
fabric softening, corrosion inhibition, emulsion compounding, and disinfection [2].
Anionic surfactants are mainly used as wetting agents, emulsifiers and detergents.
Cationic surfactants have positively charged organic ions when dissociated in water.
Anionic surfactants, on the other hand, have negatively charged ions.
Anionic surfactants can further be divided into two categories—soapy and non-soapy.
Soapy surfactants are the salts of naturally occurring fatty acids. Non-soapy surfactants
include synthetic surfactants composed of long-chained hydrocarbons which have been
sulphonated or sulfated. There are many varieties of non-soapy surfactants since they
can contain many types of functional groups—aromatics, esters, amides or any combination of the above. Anionic soapy surfactants, such as carboxylate soaps, are extensively
used in household washing, and in the mining industry as promoters for the separation
of minerals by flotation.
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