Micells shape

Unimolecular micelles are defined as a class of dendritic macromolecules, wherein an interior hydrophobic core is surrounded by a hydrophilic surface layer. These structures closely resemble the shape of classical micelles (shape,... 

Miller et al have reported that in bile salt solutions in the presence of EL, if the EL concentration is less thcin half of that of the bile salts, the mixed micelle shape beccmes spherical, but, otherwise, the shape is a disk as shown in Figure 2. All solutions used here inclixie 32 mM lecithin and 100 mM total bile salts, therefore the micelle shape in all systems here must be spherical. Edward et al... 

Zoeller, N. J., and D. Blankschtein. 1998. Experimental determination of micelle shape and size in aqueous solutions of dodecyl ethoxy sulfatdsangmuirl4 7155-7165. 

S. Ikeda, S. Ozeki and M. Tsunoda, Micelle molecular weight of dodecyldimethylammonium chloride in aqueous solutions, and the transition of micelle shape in concentrated NaCl solutions, J. Colloid Interface Sci. 73 (1980) 27-37. 

The viscosity starts to increase above the CMC and it is well established that the viscosity of a colloidal solution can give information on size and shape of the particles. From studies of the viscosity as a function of micellar concentration, the intrinsic viscosity may be obtained by extrapolation. The intrinsic viscosity depends on a shape factor, and the micelle specific volume and viscosity studies are therefore used to determine micelle shape and hydration. In many cases, these factors appear to be quite constant over a wide concentration range above the CMC. In other cases, such as hexadecyltrimethylammonium bromide (Fig. 2.9), dramatic increases in viscosity are observed at higher concentrations35). Studies of surfactants with low... 

The electrical conductance shows a weaker concentration dependence above than below the CMC corresponding to a decrease in the equivalent conductance (Fig. 2.10). The transport number of the surfactant ion rises sharply at the CMC while that of the counterion may become negative. This as well as electrophoretic mobilities may yield information on micellar charge. At high concentrations, conductance anisotropies have been observed for flowing systems. This, as well as flow birefringence, is useful for the demonstration of nonspherical micelle shape. 

Fig. 4.2. Mean radius of gyration plotted versus the mean hydrodynamic radius for different micelle shapes according to theoretical predictions (solid lines). Circles give experimental quasi-elastic light scattering results for SDS micelles at different temperatures in 0.6 M NaCl. (From Ref.34 )...

The hydration numbers given are somewhat approximative and are subject to error due to e.g., electroviscous effects and micelle shape effects. However, it seems that possible corrections should lower these numbers which can therefore serve as... 

One of our goals in applying FTTR spectroscopy to the study of micelle shape changes is to obtain data which addresses simultaneously methylene chain ordering (conformation), and headgroup spacing, for a comparison with these models. 

In water (normal micelles) Shape of the micelle In hydrocarbons RMs... 

In the simplest liquid-crystalline phase, namely the uniaxial nematic, there is at rest a special direction designated by a unit vector n called the director (see Fig. 10-2). In the plane transverse to the director, the fluid is isotropic. The most common nematics are composed of oblong molecules that tend to point in a common direction, which defines the director orientation. Oblate, or disc-like, molecules can also form uniaxial nematics for these discotic nematics, the director is defined by the average orientation of the short axis of the molecule. Lath-like molecules or micelles (shaped like rectangular slabs), in which all three dimensions of the molecule are significantly different from each other, can form biaxial nematics (Praefcke et al. 1991 Chandrasekhar 1992 Fialtkowski 1997). A biaxial... 

Another possible extension is to consider an excess oil phase which is a mixtnre of two or more species. Provided that mixing within the micelle can still be considered ideal and that activity coefficients for all species in the bulk oil mixture are known, an expression for for each solnte is readily obtained. Micelles formed from surfactant mixtures can be treated provided that micelle composition is known or can be calculated from theories of mixed micelles such as regular solution theory and that solubilization is low enough not to affect micelle shape or composition. Finally, nonideal mixing in the micelles can be included if some model for the nonideality is available as well as data for evaluating the relevant parameters. Perhaps the simplest scheme for incorporating nonideality with nonpolar solutes is to use volume fractions instead of mole fractions in the spirit of Flory-Huggins theory. 

Micelle size (aggregation number) varies according to micelle shape and alkyl chain length. Spherical micelles always have low aggregation numbers, due to the micelle ra-... 

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