Micelle segmental mobility

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies (see Chapter 8) aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic non-ionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. Information on the orientation of chains in solid polymers can also be obtained. 

Additional information on potential alterations of chain conformations or core/ corona interface due to micellisation can also be gained. Similarly, the application of NMR spectroscopy for the study of chain dynamics in micellar systems is based mainly on the fact that block copolymer segment mobility is directly correlated to the intensity of respective NMR spectrum peaks. Thus, when the core of the micelles is formed and the mobility of the insoluble blocks is significantly reduced, the intensity of the corresponding NMR peaks is reduced accordingly. 

Another relatively new lipophilicity scale proposed for use in ADME studies is based on MEKC [106]. A further variant is called BMC and uses mobile phases of Brij35 [polyoxyethylene(23)lauryl ether] [129]. Similarly, the retention factors of 16 P-blockers obtained with micellar chromatography with sodium dodecyl sulfate as micelle-forming agent correlates well with permeability coefficients in Caco-2 monolayers and apparent permeability coefficients in rat intestinal segments [130]. 

The last feature about micellar dynamics is related to the local mobility of chain segments in the core or in the corona of the micelles. SAXS, SANS, and fluorescence techniques have proven to be effective for obtaining information about chain conformation and dynamics in the different micellar... 

Reverse micelles from PMAA and PAA-containing copolymers have been extensively studied by Eisenberg and coworkers [104,105]. These authors considered the micellization of the so-called "block ionomers formed of a major PS block linked to ionized PAA and PMAA segments. Stable spherical micelles were formed by these copolymers in organic solvents such as toluene. Their characteristic size was systematically investigated by a combination of experimental techniques including TEM, SAXS, DLS, and SLS. The micelles were shown to consist of an ionic core and a PS corona. The mobility of the PS segments located near the ionic core was found to be restricted, as discussed in Sect. 2.4. 

Nuclear magnetic resonance (NMR) has been used to study segmental motions in block copolymer solutions. The mobility of protons in polymer chains in dilute solutions has been probed using high-resolution H NMR. Association of chains into micelles leads to a reduction in mobility in the core, which leads to a broadening of the respective NMR lines that has been studied for a number of systems, as described by Tuzar and Kratochvil (1993). The sol-gel transition in concentrated solutions has been located via ]H transverse relaxation time experiments, as outlined in Chapter 4. 

In this study more attention was paid to the possible formation of fringed micelle crystallites by rigid segments of RIM formulations. These crystallites could be considered to be an important factor inhibiting the mobility of the reactive groups and consequently causing the deviations from the straight line dependence of the second order reaction kinetic plot. 

The fringed micelle crystallites formed by aggregation of rigid segments would not only restrict the mobility of the reactive groups, but would also introduce physically bonded crosslinks into the amorphous polymer matrix (4,5,6). 

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