Topological micelles

Newkome GR, Moorefield CN, Baker GR, Johnson AL, Behera RK. Chemistry of micelles. 11. Alkane cascade polymers with a micellar topology micelle acid derivatives. Angew Chem 1991 103 1205-1207. 

Two system-dependent interpretative pictures have been proposed to rationalize this percolative behavior. One attributes percolation to the formation of a bicontinuous structure [270,271], and the other it to the formation of very large, transient aggregates of reversed micelles [249,263,272], In both cases, percolation leads to the formation of a network (static or dynamic) extending over all the system and able to enhance mass, momentum, and charge transport through the system. This network could arise from an increase in the intermicellar interactions or for topological reasons. Then all the variations of external parameters, such as temperature and micellar concentration leading to an extensive intermicellar connectivity, are expected to induce percolation [273]. 

Furthermore, Oda et al. pointed out that there are two topologically distinct types of chiral bilayers, as shown in Figure 5.46.165 Helical ribbons (helix A) have cylindrical curvature with an inner face and an outer face and are the precursors of tubules. These are, for example, the same structures that are observed in the diacetylenic lipid systems discussed in Section 4.1. By contrast, twisted ribbons (helix B) have Gaussian saddlelike curvature, with two equally curved faces and a C2 symmetry axis. They are similar to the aldonamide and peptide ribbons discussed in Sections 2 and 3, respectively. The twisted ribbons in the tartrate-gemini surfactant system were found to be stable in water for alkyl chains with 14-16 carbons. Only micelles form... 

The discovery of new controlled polymerization techniques in the mid-1990s and the progress achieved in living polymerization toward well-defined block copolymers with complex topologies have certainly played a key role in the development of block copolymer micelles. 

One of the possible alternative to micelles are spherical dendrimers of diameter generally ranging between 5 and 10 nm. These are highly structured three-dimensional globular macromolecules composed of branched polymers covalently bonded to a central core [214]. Therefore, dendrimers are topologically similar to micelles, with the difference that the strnctnre of micelles is dynamic whereas that of dendrimers is static. Thus, unlike micelles, dendrimers are stable nnder a variety of experimental conditions. In addition, dendrimers have a defined nnmber of fnnctional end gronps that can be functionalized to prodnce psendostationary phases with different properties. Other psendostationary phases employed to address the limitations associated with the micellar phases mentioned above and to modnlate selectivity include water-soluble linear polymers, polymeric surfactants, and gemini snrfactant polymers. 

With monomeric molecules, the aggregation number of micelles is determined by equilibrium thermodynamics. In polymeric molecules, however, topological constraints are imposed on the system. If the degree of polymerization exceeds the aggregation number of the monomeric micelle, unsaturated sites of the polymeric molecules become available (directed to the aqueous phase) and inter-molecular interactions (agglomeration) occur. In the case of polymer with Mw= 6.23x105, typical surfactant behavior was found. 

Table 7. Proposed reaction scheme for topological transformation during micelle formation in nonpolar solvents. AOT in C6H12 [Ber. Bunsenges. Physikal. Chem. 79, 667 (1975)]... 

The kinetic complexity seen in oriented micelles persists in inverse micelles. The distribution of electron transfer quenchers within the water pool follows Poisson statistics and enables the kinetic data to describe migration rates to and from the aqueous subphase [65]. These orientation effects also make possible topological control of non-electron transfer photoreactions occurring within AOT micelles [66]. 

The present review deals with the association behavior of polyelectrolyte block copolymers which is the most outstanding feature of this class of polymers. It leads to the formation of micelles, strings, and networks of sometimes quite complicated topology. The association behavior depends on many external parameters, among them pH, temperature, and salinity, which are of relevance in many technological and biological processes. 

Finally, amphiphilic graft copolymers will be reviewed and compared to the linear block copolymer structures of the same composition and it will be shown that micellization depends not only on composition, pH, and ionic strength, but also significantly on the topology of the polymer molecule. 

The molecular sieves with uniform mesopores are attractive substrates for the researches on ion adsorptions. The mesoporous silicas with various pore-connecting topologies have been prepared by templating with surfactant micelles. Grafting technique of silanes introduces funetional groups into the pores of such silicas. Divalent cations, Cu, Zn,... 

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