Internal Structures of Micelles

The unterstanding of amphiphile association clearly must include detailed knowledge of the internal structure and dynamics, e.g., what is the conformation of the alkyl chains and what are their flexibility and packing conditions is the interior of micelles exclusively of hydrocarbon nature or is there any water penetration We will here consider the state of the hydrocarbon chains and defer a discussion of water penetration to the section on hydration. 

Much of the early discussion of micelle structure centered around the problem of whether the hydrocarbon part should be considered as solid-like or liquid-like, the latter referring to conditions similar to those in liquid alkanes. Up to high alkyl chain lengths, the melting points of the alkanes lie below ambient temperature thus providing an indication that there is a liquid-like interior. However, the constraint offered by the micelle surface may, of course, substantially change the conditions. 

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Xing, L. and W L. Mattice. 1998. Large internal structures of micelles of triblock copolymers with small insoluble molecules in their corelsangmuir14 4074-4080. 

However, joining of K-casein to any of other caseins via its hydrophobic region leads to the termination of micelle growth because /c-casein just owns 1 hydrophobic segment and does not interact with CCP nanoclusters due to the lack of phosphoseiyl residues [2, 40]. This model is basically different in comparison with previous models in term of internal structure of micelles however, the cement role of CCP and location of K-casein on the surface of micelle are identical. 

Figure 1 Schematic structures of micelle and liposome, their formation and loading with a contrast agent, (a) A micelle is formed spontaneously in aqueous media from an amphiphilic compound (1) that consists of distinct hydrophilic (2) and hydrophobic (3) moieties. Hydrophobic moieties form the micelle core (4). Contrast agent (asterisk gamma- or MR-active metal-loaded chelating group, or heavy element, such as iodine or bromine) can be directly coupled to the hydrophobic moiety within the micelle core (5), or incorporated into the micelle as an individual monomeric (6) or polymeric (7) amphiphilic unit, (b) A liposome can be prepared from individual phospholipid molecules (1) that consists of a bilayered membrane (2) and internal aqueous compartment (3). Contrast agent (asterisk) can be entrapped in the inner water space of the liposome as a soluble entity (4) or incorporated into the liposome membrane as a part of monomeric (5) or polymeric (6) amphiphilic unit (similar to that in case of micelle). Additionally, liposomes can be sterically protected by amphiphilic derivatization with PEG or PEG-like polymer (7) [1].

The internal structure of polyelectrolyte block copolymer micelles such as their core radius Rc and micellar radius Rm can be determined by a variety of methods involving static and dynamic light scattering (SLS, DLS), small-angle X-ray (SAXS) and neutron scattering (SANS) as well as imaging techniques such as transmission electron microscopy (TEM) or atomic force mi-... 

It is usually assumed that the micellar corona is a continuous phase extending from the micellar core to the micellar radius Rm. The internal structure of the micelle can be described by a density profile as shown in Fig. 8. The micellar core is a homogeneous melt or glass of insoluble polymer blocks. For hydrophobic blocks in aqueous solutions, the polymer volume fraction in the micellar core is 0C 1. The micellar shell is swollen with water or aqueous salt solution and has a polymer segment density that is expected to decrease in the radial direction as 0(r) r-a as typical for star polymers or... 

Precrosslinked" or "intramolecularly crosslinked" particles are micronetworks [1]. They represent structures intermediate between branched and macroscopically crosslinked systems. Their overall dimensions are still comparable with those of high molecular weight linear polymers, the internal structure of micronetworks (p-gels), however, resembles a typical network [2]. Synthesis is performed either in dilute solution or in a restricted reaction volume, e.g., in the micelles of an emulsion. Particle size and particle size distribution can be controlled by reaction conditions. Functional groups can be... 

When neutron scattering of a sample is combined with contrast variation, information can be obtained not only about the shape and size of the micelle but also about its detailed (internal) molecular architecture. Because of the unique level of information about micellar systems that can be obtained from SANS experiments, the technique is now an extremely well-established tool for investigating the shape, size, and, to a lesser extent, the internal structure of micellar aggregates with several hundreds of papers being published since the 1970s when micelles were the first colloidal systems to be studied using SANS. 

M. C. Woods, J. M. Haile, and j. P. O Connel, ]. Phys. Chem., 90, 1875 (1986). Internal Structure of a Model Micelle via Con iputer Simulation. 2. Spherically Confined Aggregates with Mobile Head Groups. 

To discuss further the shape and internal structure of the micelles, the hydrodynamic radii calculated from the self-diffusion coefficients according to Equation 10.2 were combined and compared with the SAXS results. The self-diffusion coefficient of a hard sphere at infinite dilution. Do, is described by [46],... 

Fig. 5.1. Schematic representation showing internal structure of a spherical micelle. Hydrophobic chains are in a condensed liquid state in the core of the micelle. Each one is linked at one end to a polar head on the other side of the interface. Typical diameter of a ball is between 30 and 50 A...

Long range colloidal-like structure. Internal layering of micelles... 

Finally, we note that structural forces are also observed in complex liquids. These may arise due to changes in the spatial distribution of micelles (227) or polyelectrolytes (228-230), or be due to the internal structure of polyelectrolyte-surfactant aggregates (211, 231). 

Voets, I. K., de Vos, W. M., Hofs, B., de Keizer, A., and Cohen Stuart, M. A. 2008. Internal structure of a thin film of mixed polymeric micelles on a solid/liquid interface. Ij Pinjs Chen 112 6937-6945. 

Also the internal structure of block-copolymer micelles, as given by the size of core and corona and the density profile in each domain, has been carefully characterized by static and dynamic light scattering [40] and by small angle neutron scattering... 

For the amphiphilic block copolymer in the non-polar selective solvent, the unpolar blocks form the corona, which provides solubilization and stabilization, while the polar or hydrophilic and functionalized blocks form the core, which is able to dissolve metal compounds due to coordination, followed by the nucleation and growth of metal particles upon reduction. Also the internal structure of block-copolymer micelles, as given by the size of core and corona and the density profile in each domain, has been carefully characterized by static and dynamic light scattering [146] and by small angle neutron scattering using contrast variation techniques [147], The micellar corona has many of the characteristics of a spherical polymer brush. 

Figure 6.5 Illustrations of nanoscale spherical assemblies resulting from block copolymer phase separation in solution are shown, along with the chemical compositions that have been employed to generate each of the nanostructures (a) core crosslinked polymer micelles (b) shell crosslinked polymer micelles (SCKs) with glassy cores (c) SCKs with fluid cores (d) SCKs with crystalline cores (e) nanocages, produced from removal of the core of SCKs (f) SCKs with the crosslinked shell shielded from solution by an additional layer of surface-attached linear polymer chains (g) crosslinked vesicles (h) shaved hollow nanospheres produced from cleavage of the internally and externally attached linear polymer chains from the structure of (g)...

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