Structure micelles

M. Zulauf, K. Weckstrom, J. B. Hayter, V. Degiorgio, M. Corti. Neutron scattering study of micelle structure in isotopic aqueous solutions of poly(oxy-ethylene) amphiphiles. J Phys Chem 29 3411-3417, 1985. 

In a class of reahstic lattice models, hydrocarbon chains are placed on a diamond lattice in order to imitate the zigzag structure of the carbon backbones and the trans and gauche bonds. Such models have been used early on to study micelle structures [104], monolayers [105], and bilayers [106]. Levine and coworkers have introduced an even more sophisticated model, which allows one to consider unsaturated C=C bonds and stiffer molecules such as cholesterol a monomer occupies several lattice sites on a cubic lattice, the saturated bonds between monomers are taken from a given set of allowed bonds with length /5, and torsional potentials are introduced to distinguish between trans and "gauche conformations [107,108]. 

The progression of an ideal emulsion polymerization is considered in three different intervals after forming primary radicals and low-molecular weight oligomers within the water phase. In the first stage (Interval I), the polymerization progresses within the micelle structure. The oligomeric radicals react with the individual monomer molecules within the micelles to form short polymer chains with an ion radical on one end. This leads to the formation of a new phase (i.e., polymer latex particles swollen with the monomer) in the polymerization medium. 

In some cases, due to the highly polar character of the sulfate radicals, peroxydisulfate initiators can provide slow polymerization rates with some apolar monomers since the polar sulfate radicals cannot easily penetrate into the swollen micelle structures containing apolar monomers. The use of mercaptans together with the peroxydisulfate type initiators is another method to obtain higher polymerization rates [43]. The mercaptyl radicals are more apolar relative to the free sulfate radicals and can easily interact with the apolar monomers to provide higher polymerization rates. 

The function of emulsifier in the emulsion polymerization process may be summarized as follows [45] (1) the insolubilized part of the monomer is dispersed and stabilized within the water phase in the form of fine droplets, (2) a part of monomer is taken into the micel structure by solubilization, (3) the forming latex particles are protected from the coagulation by the adsorption of monomer onto the surface of the particles, (4) the emulsifier makes it easier the solubilize the oligomeric chains within the micelles, (5) the emulsifier catalyzes the initiation reaction, and (6) it may act as a transfer agent or retarder leading to chemical binding of emulsifier molecules to the polymer. 

According to the other kinetic model proposed for the soapless emulsion process, the growing macroradicals may also form micelle structures at earlier polymerization times since they have both a hydrophilic end coming from the initiator and a hydrophobic chain [74]. 

Therefore, the polymerization progresses within the micelle structure by following the traditional mechanism of emulsion polymerization. 

Farrell, H. M., Jr., Malin, E. L., Brown, E. M., and Qi, P. X. (2006). Casein micelle structure What can be learned from milk synthesis and structural biology Curr. Opin. Colloid Interface Sci. 11,135-147. 

Horne, D. S. (2009). Casein micelles structure and stability. In "Milk Proteins From Expression to Food", (A. Thompson, M. Boland, and H. Singh, Eds), pp. 133-179. Academic Press, San Diego. 

McMahon, D. J. and McManus, W. R. (1998). Rethinking casein micelle structure using electron microscopy. /. Dairy Sci. 81,2985-2993. 

Figure 15.12 Detergent molecules can be used to solubilize carbon nanotubes by adsorption onto the surface through hydrophobic interactions and create half-micelle structures with the hydrophilic head groups facing outward into the aqueous environment.

Ester saponifaction was a favoured reaction for this type of study, because the hydrophobicity of the acyl moiety could easily be controlled by increasing the length of an n-alkyl group, and saponification of p-nitrophenyl n-alkanoates could be followed with very dilute substrate. Substrate concentration is an important factor, because provided that it is kept low it is reasonable to assume that the micelle structure is relatively unperturbed. 

The micelle formation is not restricted to solvents for polystyrene but also occurs in very unpolar solvents, where the fluorinated block is expected to dissolve. Comparing the data, we have to consider that the micelle structure is inverted in these cases, i.e., the unpolar polystyrene chain in the core and the very unpolar fluorinated block forming the corona. The micelle size distribution is in the range we regard as typical for block copolymer micelles in the superstrong segregation limit.2,5,6 The size and polydispersity of some of these micelles, measured by DLS, are summarized in Table 10.3. 

Scheme 2 Thermoresponsive polymeric micelle structures and fimctions.

Cammas, S., Suzuki, K., Sone, Y, Sakurai, Y., Kataoka, K., and Okano, T. Thermo-responsive polymer nanoparticles with a core-shell micelle structure as site-specific drug carriers. J. Contr. Rel, 1997,48, 157-164. 

Figure 1.2 Structure of a mixed bile-acid/fatty-acid micelle, whereby the hydrophilic (OH groups of BA) are radially arranged on the outside of the micelle and the hydrophobic moieties are arranged on the interior. As well as a classic micelle, a cylindrical mixed micelle structure is also shown.

FIGURE 3.17 Micelle structure (A) (inner part = liquid paraffin-like outer polar part) (B) solubilization of apolar molecule (C) binding of counterion to the polar part (schematic). 

Home, D.S. (2006). Casein micelle structure models and muddles. Current Opinion in Colloid and Interface Science, 11, 148-153. 

Nature itself gives us a spectacular example of a biopolymer-based delivery system in the form of the native casein micelle of mammalian milk (Lemay et al, 2007). This is primarily a colloidal delivery system for calcium, where the micronutrient is in the form of calcium phosphate, which does not give a bitter taste, and which provides good bioavailability owing to its colloidal size, amorphous state and quick dissolution in gastric conditions (pH 1-2). Nevertheless, the casein micelle structure is unique there are no other readily available natural delivery systems for most nutraceuticals. Therefore some new designs are clearly required (Velikov and Pelan, 2008 McClements et al, 2008, 2009). 

Marchin, S., Putaux, J.L., Pignon, F., Leonil, J. (2007). Effects of the environmental factors on the casein micelle structure studied by cryo-transmission electron microscopy and small-angle X-ray scattering/ultra-small-angle X-ray scattering. Journal of Chemical Physics, 126, 45-101. 

Schmidt, D.G. (1982). Association of caseins and casein micelle structure. In Fox, P.F. (Ed.). Developments in Dairy Chemistry. London Applied Science, pp. 61-86. 

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