Micelle dimensions

The transition from spherical to rod-like micelles changes the dimensionality of the diffusion space and affects the reaction dynamics [84]. The decay kinetics were predicted to follow approximate biphasic first-order kinetics, with the separate components corresponding to the two characteristic micelle dimensions. This behavior has been verified experimenfally [85[. 

Control of the micelle size utilized in the formation of PAn nanoparticles has been achieved by tailoring the stabilizer to modify the resulting micelle dimensions. Kim and coworkers215 216 used amphiphilic polymer molecules and hydrophobically end-capped polyethylene oxide) [PEO], and varied the hydrophilic regions in it to control the final micelle size. The resultant nanostructures ranged from 20 to approximately 300 nm in size, depending on the molecular weight of the hydrophilic PEO midsection. 

Lyotropic nematic phases are generally found for short chain surfactants, for both hydrocarbon or fluorocarbon derivatives [55, 56]. Two different micelle shapes can occur (Fig. 10) [57]. One type (N. ) is thought to be composed of small cylindrical micelles and is related to the hexagonal phase, while the other type of nematic (Nj) is composed of planar disc micelles and is related to the lamellar phase. Note that the disc micelles are likely to be matchbox or ruler shaped , rather than the circular discs. Hence the disc nematic phase can have the director along the long axis of ruler micelles or along the shortest micelle dimension, as with match box micelles, while with phases the director always lies... 

A diverse range of theoretical approaches have been employed to analyze the structure of block copolymer micelles, and for micelle formation (1). The first models were based on scaling relationships for polymer brushes and give predictions for the dependence of micelle dimensions on the size of the blocks, as well as the association nnmber of the micelle. A l3rnsh theory by Leibler and coworkers enables the calcnlation of the size and nnmber of chains in a micelle and its free energy of formation (124). The fraction of copolymer chains aggregating into micelles can also be obtained. Self-consistent field theory was first applied to predict the critical micelle concentration of a diblock in a homopolymer matrix, and then applied to block copolymers in solution (1). The lattice implementation of SCF theory has been applied to analyze the dimensions of micelles for specific (Pluronic) block copolymers (125). 

The micelle dimension are easily adjustable in the range of 10-100 nm, which is a major requirement for injectable formulations. 

The most important consequence of micelle formation in the process of emulsion polymerisation is the solubilisation of organic compounds in aqueous media. Since the association of lipophilic groups inside a micelle leads to a formation of centres of attraction for organic compounds, it is possible to dissolve appreciably higher proportions of sparingly water-soluble monomers in micellar solutions than in water alone. Monomers, which are essentially non-polar in character, may be expected to dissolve only inside the hydrocarbon portion of the micelle. Compounds with polar groups can at least partially be accommodated in the water phase or at the micelle surface so that the requirements for the micelle dimensions are less critical. 

The solubilization of decanol and toluene in micellar solutions of surfactant [Q] with X = OH was investigated by small-angle neutron seattering (SANS). The micelles were modeled as spheres (for toluene solubilization) and cylinders (for decanol solubilization) in order to fit the SANS data. A growth of the micelle dimensions was thus evidenced upon addition of toluene and decanol [100]. 

Such a micelle acts like an oil drop in an aqueous solution and allows solubilization of organic compounds present in the aqueous solution into the hydrophobic interior. If the surfactant is ionic, i.e. either cationic or anionic, then oppositely charged ionic species, namely counterions from the solution, will be adsorbed on the surface of the micelle or bind with the charged micellar surface. Such surfrice binding will effectively Increase the micelle dimension. A unique number of surfrictant molecules between 50 and 100 aggregate to form a micelle. 

Lianos P and Thomas J K 1986 Cadmium sulfide of small dimensions produced in inverted micelles Chem. Phys. Lett. 125 299... 

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