TABLE OF CONTENTS Surfactant molecules are amphiphilic; that is, they possess hydrophilic (water-loving) groups chemically bonded to lyophilic (oil-loving) groups. A typical lyophilic group is a slender hydrocarbon chain of length 8-20 carbon atoms, frequently called a surfactant "tail," The hydrophilic group is usually short and bulky and is often called the "head," Some examples of amphiphiles are listed in Table 12-1; the head groups are underlined. Table 12-1 includes anionic, cationic, and nonionic surfactants, and the last entry in Table 12-1 is a two-tailed surfactant. In a watery milieu, the tails huddle together to minimize their exposure to water. The reverse occurs in oil.
Thus, in solutions, amphiphiles self-assemble into aggregates such as spheroidal and worm-like micelles, vesicles, and bilayers (see Fig. 12-1). At high concentrations, such aggregates can form ordered phases of nematic, hexagonal, smectic, cubic, or other symmetry (Seddon 1990; Berret et al. 1995). Amphiphiles are not only of great interest scientifically, but are of immense practical value as detergents, emulsifiers, encapsulants, lubricants, and so on. Long, worm-like micelles act like "living polymers" that is, polymers that can reassemble themselves from their constituent surfactant molecules even after being torn to pieces, say, by a strong flow field. Such self-assembling "polymers" have possible applications as viscosifiers or as drag reducing agents that suppress turbulence in flows that might irreversibly fragment ordinary drag-reducing polymers (Zakin et al. 1996). Bilayers composed of phospholipids which are fatty-acid-derived surfactants serve biological functions as membranes in animal and plant cells. The double-tailed phospholipids...
