Contiguous versus segmented hydrophobicity in micellar systems.

This paper addresses a question not yet posed systematically in surfactant chemistry: How do the colloidal properties of surfactants respond to insertion of non-hydrocarbon functionalities (i.e., ester groups) within chains that are normally entirely hydrocarbon? In answering this question, two classes of such chain-modified surfactants were discovered. One class forms only small aggregates with noncooperative self-assembly, low foaming, high areas of occupancy at the air/water interface, and weak solid-adsorption and solubilization properties. The other class is much more normal with regard to these properties and, in fact, can even exceed conventional surfactants in mesitylene solubilization. Differences between the two categories of chain-modified surfactants originate from the degree of segmentation of the hydrocarbon and, in particular, upon the location of the longest segment. Segmented hydrophobicity, having in principle a "hydrophobic potential" similar to that of a contiguous hydrophobicity of equal length, can induce aggregation but, concurrently, alters the mode of assembly into films and micelles.