Headgroup area interactions

Rod micelle formation is promoted in mixtures of surfactants when there is either a large reduction in the headgroup areas, or an increase in the methylene tail volume, and thus, in terms of the surfactant-surfactant interaction parameters, is favored by large negative values of p. The forces which hold micelles together are... 

In the past few years, a range of solvation dynamics experiments have been demonstrated for reverse micellar systems. Reverse micelles form when a polar solvent is sequestered by surfactant molecules in a continuous nonpolar solvent. The interaction of the surfactant polar headgroups with the polar solvent can result in the formation of a well-defined solvent pool. Many different kinds of surfactants have been used to form reverse micelles. However, the structure and dynamics of reverse micelles created with Aerosol-OT (AOT) have been most frequently studied. AOT reverse micelles are monodisperse, spherical water droplets [32]. The micellar size is directly related to the water volume-to-surfactant surface area ratio defined as the molar ratio of water to AOT,... 

Due to their structure (Figure 17.1), all surfactants have the tendency to accumulate at interfaces because there the hydrophobic tail can be shielded from interacting with water molecules while the hydrophilic headgroup remains solvated by water molecules. As a result of this orientation, surfactant molecules displace water molecules at the interface. Consequently, the number of hydrogen bonds decreases per unit interface area. This can be... 

Comparing CMCs of a nonionic and an ionic surfactant with approximately equal head-group area (C12E08, C12Pyr and C12E02S0y) makes it apparent that the CMC of the nonionic surfactant is the lowest. It also demonstrates the effect of electrostatic repulsion. While hydrophobic interactions drive micellization, they are counteracted by steric and electrostatic interactions of the headgroups, both of which limit the coverage of the interface with surfactant molecules. 

The effect of cholesterol on the thermotropic phase behavior of PC bilayer also varies significantly with the structure, particularly the degree of unsaturation, of the hydrocarbon chains, with more highly unsaturated PCs exhibiting a reduced miscibility with cholesterol and other sterols. Moreover, the structure of the lipid polar headgroup is also important in determining the effect of cholesterol on the host lipid, as is the structure of the sterol molecule itself. For more information on the application of DSC to the biologically important area of lipid-sterol interactions, the reader is referred to recent reviews (23-25). 

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