Soaps and detergents form association colloids in water. Their molecular structure is similar to the illustration below, where the carboxylic acid group is the hydrophilic portion and the hydrocarbon chain is the hydrophobic part of the molecule. Sodium salt of a carboxylic acid, a compound that form association colloids when placed in water. Figure 3, below illustrates association colloids in suspension. Association colloids suspended in solution .
Colloids are of interest to the environmental chemist for several reasons.
Both organic and inorganic substances are transported as colloids. Although most pesticides and herbicides are not water soluble, they do aggregate with humic and fulvic acids, natural breakdown products of cellulose. Humic and fulvic acids form hydrophilic colloids in water, transporting pesticides and herbicides in the process. Clays are the most common hydrophobic colloids in natural waters. Clay is a generic term used to describe a class of secondary minerals produced from the weathering of aluminum silicate rocks.