Micellization of block copolymer

Riess, G., Micellization of block copolymers. Progress in Polymer Science 2003, 28, 1107-1170. 

Much recent work on micellization in block copolymers has been focussed on this industrially important type of polymer. We therefore describe experiments on micellization in aqueous solutions of poly(oxyalkylene) diblocks and triblocks in some detail. This serves to illustrate many of the important features of micellization of block copolymers, also observed in other systems such as the styrenic block copolymers covered in the following section. 

Among other approaches, a theory for intermolecular interactions in dilute block copolymer solutions was presented by Kimura and Kurata (1981). They considered the association of diblock and triblock copolymers in solvents of varying quality. The second and third virial coefficients were determined using a mean field potential based on the segmental distribution function for a polymer chain in solution. A model for micellization of block copolymers in solution, based on the thermodynamics of associating multicomponent mixtures, was presented by Gao and Eisenberg (1993). The polydispersity of the block copolymer and its influence on micellization was a particular focus of this work. For block copolymers below the cmc, a collapsed spherical conformation was assumed. Interactions of the collapsed spheres were then described by the Hamaker equation, with an interaction energy proportional to the radius of the spheres. 

Manners, Winnick, and their collaborators22 have studied the self-assembly into cylindrical micelles of block copolymers formed from poly(ferrocenylsilanes) (R/R = Me/Me) and poly(dimethylsiloxane). By ensuring that the poly(dimethylsiloxane)... 

Fig. 1 Important parameters in the micellization of block copolymers. A is the insoluble block forming the micellar core, B is the soluble block forming the micellar shell or corona. Symbols are explained in the text...

Riess G (2003) Micellization of block copolymers. Prog Polym Sci 28 1107-1170... 

Finally, Mattice and coworkers have used lattice Monte Carlo simulations for various studies of micellization of block copolymers in a solvent, including micellization of triblock copolymers [43], steric stabilization of polymer colloids by diblock copolymers [44], and the dynamics of chain interchange between micelles [45]. Their studies of the self-assembly of diblock copolymers [46-48] are roughly equivalent to those of surfactant micellization, as a surfactant can in essence be considered a short-chain diblock copolymer and vice versa. In fact, Wijmans and Linse [49,50] have also studied nonionic surfactant micelles using the same model that Mattice and coworkers used for a diblock copolymer. Thus, it is interesting to compare whether the micellization properties and theories of long-chain diblock copolymers also hold true for surfactants. 

Contrary to the case of equdibrium kinetics, micellization of block copolymers proceeds from unimers and potentially involves any aggregate size up to or even above the equUibrium size. Hence, a theoretical treatment of the problem involves finding the concentration of the set of aggregates at all times ( i(0,< 2(0- max(0 TWs is a quite challenging task, for which the detailed... 

Riess, G. (2003). Micellization of block copolymers. ProgPolym Sci, 28, 1107-1170. Allen, C., Maysinger, D. Eisenberg, A. (1999). Nano-engineering block copolymer... 

For ionic snrfactants, the addition of short-chain alcohols decreases Xj (i.e., inereases xj ). For medium-ehain alcohols, X2 initially increases with inereasing aleohol eonemtration, then reaches a maximum and decreases as additional alcohol is incorporated into the micelle interior instead of the paUsade layer. The addition of hydroearbons, which are solubilized in the micelle interior, also prodnees a decrease in xj. In Chapter 6 we call attention to the fact that even thongh Xj is qnite small, its effect can be felt even in slow processes such as solubilization, wave motion, etc. It is noteworthy that micelles of block copolymer, PEO-PPO-PEO, also show these two time constants, which have similar intmpretations (Goldmints et al., 1997). 

In consideration of the thermodynamic aspects, and from the early results of Price [5] and Quintana et al. [ 135], it is now well established that the micellization of block copolymers in organic medium is an enthalpic driven process, the micellar core formation being the main contribution to the exothermic process. 

Since then, the research has dramatically grown and many goals have been achieved. A review reports an organized and detailed overview on theoretical aspects and basic principles of self-assembly and micellization of block copolymers in solution, together with a wide number of examples concerning the methods for the stabilization of macromolecular aggregates and their applications, mainly focused on biomedical field, in the perspective of smart nano-objects production [37]. The self-organization of block copolymers in different shapes is depicted in Fig. 1.4. 

II. THEORETICAL ASPECTS OF THE DYNAMICS OF MICELLES OF BLOCK COPOLYMERS... 

Hsieh M.F, Cuong N.V et al. (2008) Nano-Sized Micelles of Block Copolymers of Methoxy Poly(ethylene glycol)-Poly(E-caprolactone)-Graft-2-Hydroxyethyl Cellulose for Doxorubicin Delivery. J. Nanosci. Nanotechnol 8 2362-2368. 

An electrochemically induced change of spherical micelles to larger aggregates was observed for coumarin-containing block copolymers [294]. Electrochemical addressability was also found for ferrocene-based micelles of block copolymers, which can undergo conjugation with hydroxylamines in terms of an oxime function [186]. After conjugation micelles are formed, whose size can be manipulated by the oxidation state of the ferrocene units (here only reported by chemical redox). 

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