Rodlike micelles

HTAB HTAB CA Solute Micelles Rodlike Particles... 

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

Figure C2.3.13. Nonnal (H, left) and inverse (H, right) hexagonal mesophases composed of rodlike micelles.

Above 0.45 NaCl a rodlike shape has to be assigned to the micelles and Eq. 19 must be used ... 

Peculiar DNA architecture was demonstrated in 25% aqueous ethanol when DNA was complexed with series of cationic detergents in the presence of poly(glutamic acid) [124]. Electron microscopy and x-ray scattering demonstrated that DNA can pack cetyltrimethylammonium bromide molecules into rodlike micelles, which form a hexagonal lattice. Interestingly, circular dichroism spectroscopy revealed that in these complexes DNA adopts left-handed conformation. 

FIG. 5 Representation of rodlike water-containing reversed micelles. 

The cobalt, nickel, and copper bis(2-ethylhexyl) phosphate surfactants dissolved in n-heptane lead to quasi-one-dimensional association microstructures, i.e., rodlike reversed micelles that increase in size via water solubilization [111],... 

Fig. 12 Spherical (a), rodlike (b), and vesicular (c) morphologies for crew-cut micelles (images downloaded from http //ottomaass.chem.mcgill.ca/groups/eisenberg/). Adapted from [35]...

Fig. 17 Formation of rodlike micelles with diameter of 25 nm from self-assembly of a protein (lipase enzyme)-polymer (PS) hybrid in THF. Reprinted with permission from [264]. Copyright (2003) American Chemical Society... 

It was recently demonstrated that noncentrosymmetric micelles can also be obtained from ABC triblock copolymers. This is illustrated by the pioneering work of Stupp and coworkers, who synthesized a miniaturized ABC triblock containing PS and PI oligomeric block linked to a third rodlike block... 

In a very recent investigation, hydrophobic PFS (Sect. 7.1) was attached to a hydrophilic PEO block to form an amphiphilic PFSi2-[Ru]-PE07o block copolymer [331]. Rodlike micelles were observed in water for this copolymer (Fig. 24). These micelles have a constant diameter but are rather polydisperse in length, and DLS measurements indicate that they are flexible. Crystallization of the PFS in these micelles was observed and is thought to be the key behind the formation of rodlike structures. The cylindrical micelles can be cleaved into smaller rods whenever the temperature of the solution is increased or whenever they are exposed to ultrasound. 

Figures 9a-c represent transmission electron micrographs of different lyotropic liquid crystals after freeze fracture without etching. The layer structure of the lamellar mesophase including confocal domains, hexagonal arrangement of rodlike micelles within the hexagonal mesophase, as well as close-packed spherical micelles within the cubic liquid crystal can be clearly seen.

The aggregates created by amphiphiles are usually spherical (as in the case of micelles), but may also be disc-like (bicelles), rodlike, or biaxial (all three micelle axes are distinct) (Zana, 2008). These anisotropic self-assembled nanostructures can then order themselves in much the same way as liquid crystals do, forming large-scale versions of all the thermotropic phases (such as a nematic phase of rod-shaped micelles). 

RP Hjelm, P Thiyagarajan, H Alkan-Onyuksel. Organization of phosphatidylcholine and bile salt in rodlike mixed micelles. J Phys Chem 96 8653-8661, 1992. 

Here, V is the volume of the hydrocarbon chain(s) of the surfactant, the mean cross-sectional (effective) headgroup surface area, and 4 is the length of the hydrocarbon tail in the all-trans configuration. Surfactants with Pcone-shaped and form spherical micelles. For l/3truncated-cone-shaped, resulting in wormlike micelles (the term wormlike is preferred over rodlike to highlight the highly dynamic nature of these micelles). 

Figure 2.6 Schematic representation of the formation of micelle and rodlike structures of amphiphilic conjugate of oligonucleotide and PPO.

It bears repeating that the values are effective diffusivities and that, in fact, diffusivity is a function of surfactant concentration, as shown by interferometry for the Li phase of Ci2(EO)5 [9]. For the anisotropic phases diffusivity is also a function of orientation, and Dej depends on the number and orientation of domains of the phase as formed during dissolution. Thus, the value shown in Table 1 for DgHi of Ci2(EO)6 is intermediate between the diffusivities parallel and perpendicular to the rodlike micelles measured in fully oriented samples of the hexagonal phase Hi for this surfactant [26]. 

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