TABLE OF CONTENTS The aggregates formed upon an increase in amphiphile [*] concentration in water beyond some critical concentration are called micelles. Figure 14.1(a) illustrates a micelle schematically. The open circles with two attached dots represent water molecules. The hydrophilic head groups of the amphiphiles are the filled circles. The hydrophobic tails are the dark lines attached to the filled circles. As shown, the hydrophobic groups are inside this roughly spherical micelle where they are shielded from the water molecules. Figure 14.1(b) shows a plot of free (unbonded) amphiphile concentration versus total amphiphile concentration of a host solution. As indicated in the figure the free amphiphile concentration remains approximately constant beyond the critical micelle concentration (CMC). The CMC is not a phase boundary. Micelles do not represent a thermodynamic phase. These statements will be explained later in this chapter. Before we proceed to this explanation it is instructive to consider the nature of the product formed at concentrations in excess of the CMC. This product differs in a significant way from that formed in a metastable solution having non-amphiphilic solute in the transition to the equilibrium state. The latter occurs either by classical nucleation and growth, or by spinodal decomposition, or by some combination of both processes. Consider the case of a metastable solution at a composition adjacent to and slightly above the binodal composition. The cores of the embryos (clusters of the stable phase) have a constant composition...
