Equilibrium, micelle-unimer

Size-exclusion chromatography (SEC) has been used to characterize the unimer-micelle distribution. However, SEC is not an absolute method and thus requires calibration. Since it is practically impossible to calibrate a SEC apparatus for the unimers and micelles formed by a block copolymer, only indicative MW values can be obtained. Moreover, several authors have noted a strong perturbation of the unimer-micelle equilibrium during SEC experiments even when interaction of the material with the SEC column was minimized [4,61,62],... 

The dynamics of micellar systems is a very important concern that is relevant at several levels. In this respect, the dynamics required for the establishment of the unimer-micelle equilibrium is one aspect. The so-called problem of micelle hybridization that deals with the exchange rate of unimers between different micelles is closely related. Finally, the chain dynamics of polymer blocks in either the core or the corona is another concern that can, however, be linked to some extent to the first two mentioned concepts. These different aspects have been scarcely studied and reviewed by Tuzar and Kratochvil [6,41], and... 

Tuzar and coworkers [305] studied the micellization of a poly(isoprene-g-styrene) copolymer in solvent mixtures selective either for the backbone or for the grafts. Their results from static and dynamic light scattering and sedimentation velocity experiments favor the closed association model for the description of the unimers-micelles equilibrium. The graft copolymer micelles were found to have lower aggregation numbers and to be less compact than the micelles formed by linear diblocks. 

A great number of experimental and theoretical studies have been published concerning the surface modification of biomedical devices by block copolymers in order to promote-spe-cific characteristics, for example wetting, improved biocompatibility, etc. For the surface modification by block and graft copolymers, it is important to determine not only the conformation and the surfaces density of the adsorbed chains in form of a brush, but also the kinetics of this phenomenon which in fact will depend on the unimer-micelle equilibrium. 

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