Micelle disks

The spherical micelles (Fig. 2.1) are the most extensively studied polymeric self-assembled stmctures. They represent the simplest and most widespread aggregate morphology. Cylindrical micelles as well as polymer vesicles (poly-mersomes) are less frequently observed (Fig. 2.1), whereas complex stmctures such as toroids, helices, multicore and multicompartment micelles, disks, tubules are considered as more or less exotic stmctures. Worth mentioning is the phenomenon of coexisting morphologies, which is believed to derive from a number of inherent for the synthetic copolymers characteristics, e.g., dispersity in molar mass. 

In many cases, under changing experimental conditions, water-containing reversed micelles evolve, exhibiting a wide range of shapes such as disks, rods, lamellas, and reverse-vesicular aggregates [15,107,108], Nickel and copper bis(2-ethylhexyl) sulfosucci-nate and sodium bis(2-ethylhexyl) phosphate, for example, form rod-shaped droplets at low water contents that convert to more spherical aggregates as the water content is increased [23,92,109,110],... 

The microheterogenous and nanoheterogenous (mesoscopic) liquid-liquid systems may be concisely called the small systems. They comprise the micro- and nanodomains, described in colloidal chemistry as a variety of structures, e.g., micelles, rods, disks, vesicles, microemulsions, monolayers, and Langmuir Blodgett layers [6,17 19,70]. 

I didn t use the triton X-100 example because it is a neutral entity. It is fine for an organic chemist, but inorganic entities can t interact with this micelle. However, a triton X-100 micelle is very well studied because biochemists are interested in using it as a model membrane since it makes big flat-disk micelles. Biochemists consider it as resembling a section of membrane, which can solubilize proteins. It is a good model for biological systems. 

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... 

Figure 2 The mixed micelles consisting of Bile salts and Lecithin. Disk Excess Lecithin. Sphere Excess Bile salts.

Test Methods. Surface tension (y) measurements were taken by Wil-helmy method (25+0.1°C). Critical micelle concentrations (cmc) were obtained from Y logC curves. Contact angle. Type GI, Japan. Wetting test. Canvas disk method, CIS,HG-2-380-66. Foam test, Ross-Miles lather method. Emulslbillty was determined by mixing 20 ml of 2.5%... 

At relatively low concentrations of surfactant, the micelles are essentially the spherical structures we discussed above in this chapter. As the amount of surfactant and the extent of solubilization increase, these spheres become distorted into prolate or oblate ellipsoids and, eventually, into cylindrical rods or lamellar disks. Figure 8.8 schematically shows (a) spherical, (b) cylindrical, and (c) lamellar micelle structures. The structures shown in the three parts of the figure are called (a) the viscous isotropic phase, (b) the middle phase, and (c) the neat phase. Again, we emphasize that the orientation of the amphipathic molecules in these structures depends on the nature of the continuous and the solubilized components. 

Block copolymers self-assemble to form nanoscale organized structures in a selective solvent. The most common structures are spheres, with the insoluble core surrounded by a solvent-swollen corona. In some instances, disk- or worm-like micelles form, and are of particular interest, since the control of their association can lead to a broad range of new applications [1,2]. An important subset of block copolymer micelles are those which contain metal atoms, through covalent attachment or by complexa-tion [3], These structures are interesting because they take advantage of the intrinsic properties of their components, such as the mechanical properties of the polymer micelles and the optical and magnetic characteristics of the metal atoms. Moreover, the assembly permits the control of the uniformity in size and shape of the nanoparticles, and it stabilizes them. 

Electron microscopy provides perfect pictures of vacuum collapsed vesicle membranes after negative staining with heavy metal salts. BLMs appear usually as collapsed balls, MLMs often as flat disks (see Figure 4.29). There is no requirement for double-chain amphiphiles in order to form vesicles. The same single-chain amphiphiles which form micelles also form vesicles if their charge is neutralized. This was practised, for example, via the protonation of soaps or through addition of an amphiphilic counterion. In both cases, fatty acids function perfectly well in the form of vesicles. 

Figure 5.14 a) The formation of linear hydrogen bond chains transforms spherical micelles to micellar disks with hydrophobic surfaces (see text). 

Williams and Fredrickson proposed the hockey puck micelle (one of the nonlamellar structure) where the rods are packed axially to form finite-sized cylindrical disk covered by coils (Figure 2).15 They... 

A spherical micelle should be rather considered as idealized picture, and non-spherical aggregates are often formed due to geometric packing requirements. Very high surfactant concentrations induce transition of spherical micelles into other shapes (rods, disks, vesicles, lamellar structures). 

Schematic models for the expanded structure of bile acid-phosphatidylcholine mixed micelles are shown in Fig. 2B. The original model was proposed by Small in 1967 (S36). In this model the mixed micelle consisted of a phospholipid bilayer disk surrounded on its perimeter by bile acid molecules, which were oriented with their hydrophilic surhices in contact with aqueous solvent and their hydrophobic sur ces interacting with the hydrocarbon chains of the phosphohpid molecules. This model has recently been revised, based on further studies of mixed micelles using quasi-elastic light scattering spectroscopy (M20). In a new model for the molecular structure of bile acid-phospholipid mixed micelles. Mazer et al. (M20) propose a mixed disk, in which bile acids are found not only on the perimeter of phospholipid bilayers, but also incorporated within their interior in high concentrations (Fig. 2B). The size of these mixed micelles was estimated to be as high as 200 to 400 A in radius in some solutions, and disk-shaped particles in this size range were observed by transmission electron microscopy (M20). Micellar aggregates similar in size and structure to those found in model bile solutions have been demonstrated in dog bile (M22).

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