Dilute isotropic solutions micelle formation

While only one paper describes the appearance of an anisotropic aqueous solution for a polymer of type D (19), polymers of type A to C have been investigated in more detail recently with respect to formation of liquid crystalline phases (20-23). In the following two sections, the association behavior in dilute isotropic solution and the liquid crystalline phase region is discussed on the basis of some experimental results. The dilute isotropic solutions are of interest with respect to the question whether polymers of type A and B form micelles similar to the corresponding monomeric amphiphiles. The liquid crystalline phase regime gives information whether the linkage of the amphiphiles via a polymer backbone influences the stability of the anisotropic phases and whether the same polymorphism occurs as is known for monomeric amphiphiles. 

There is some disagreement within the surfactant literature as to the exact definition of solubilization, particularly as the ratio of surfactant to additive decreases, and one approaches the nebulous frontier between swollen micellar systems and the micro- and macroemulsion regions. For present purposes, solubilization will be defined as the preparation of a thermodynamically stable, isotropic solution of a substance (the additive ) normally insoluble or only slightly soluble in a given solvent by the addition of one or more amphiphilic compounds at or above their critical micelle concentration. By the use of such a definition, a broad area can be covered that includes both dilute and concentrated surfactant solutions, aqueous and nonaqueous solvents, all classes of surfactants and additives, and the effects of complex interactions such as mixed micelle formation and hydrotropes. It does not, however, limit the phenomenon to any single mechanism of action. 

Chapter 4 discussed the formation of relatively small, uniform, or isotropic association structures or micelles in dilute surfactant solutions. We know, however, that surfactants and related amphiphilic molecules, including the naturally occurring lipids, some proteins, and a variety of combined natural chemical species, tend to associate into structures more extensive than simple micelles in both aqueous and nonaqueous environments. In many cases, such assembUes can transform from one type to another as a result of sometimes subtle changes in solution conditions such as (1) changes in the concentration of the amphiphilic components, (2) the addition of new active components, (3) changes in solvent composition, (4) the addition of electrolytes, (5) temperature changes, (6) changes in solution pH, and (7) unspecified influences from internal and external sources—such as the phase of the moon, or so it seems at times. 

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