Micellar Morphology

The most abundant micellar morphology is that of spherical micelles [1, 10]. The self-assembly of a classical amphiphilic diblock copolymer AB (A and B denote the two different blocks) leads to two different micellar structures, depending on the relative length of the blocks. These two types of spherical micelles are schematically presented in Fig. 2. When the soluble block A is larger than the insoluble 

It is quite evident that both micellar structures can be obtained by the same amphiphilic diblock copolymer system only by changing the structural parameters of the AB copolymer. The relative lengths of the two blocks and the total of the copolymer not only dictate the morphology of the resulting micelles ( hairy vs. crew-cut ) but also determine the rest of the micellar characteristics (Aagg, 

Spherical micelles can also result from the self-assembly of triblock copolymers of the ABA type. When these copolymers are dissolved in a selective solvent for the outer A blocks, they form starlike micelles, as seen in Fig. 3a. The situation is more complex for the micellisation of ABA copolymers in a selective solvent of the middle B block. If the concentration of the copolymer is low and/or the A blocks have a relatively small My, isolated flower-Uke micelles can be assembled, where the B block is looped and the A blocks participate in the same micellar core (Fig. 3b). However, an increase in the cmicentration of the copolymer or the My, of the A blocks could lead to micelle association into larger aggregates due to partial conversion from loops to bridges, i.e. the A blocks of the copolymer chain can be located in two different micellar cores (Fig. 3c). Both theoretical [14] and experimental investigations of the self-assembly of ABA triblock copolymers have been carried out, e.g. studies on PAl-PS-PAI copolymers dissolved in DMF [15], as well as PBO-PEO-PBO in water [16, 17]. 

The introduction of a third block leads to another intriguing class of triblock copolymers that of the ABC type, since it can provide interesting new functionalities and higher diversity of micellar organisations. Depending on the selective solvent, one or two of the triblock copolymer blocks can be insoluble. In the first case, micelles with a compartmentalised corona are formed, while in the second 

Polymer vesicles or polymersomes constitute an extremely interesting class of macromolecular self-assembly, and since their first observation 20 years ago [35], they have attracted a rapidly increasing degree of scientific attentirm. This is mainly because of their resemblance to natural cellular membranes, the ability to control their size along with their interactions with the environment, their tailorable membrane properties, as well as their versatile potential applications spanning from (bio-) electronics and catalysis to medical therapy. In the last decade, the 

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SEES with oil leads to the transition from lamellar morphology to micellar morphology [15]. This transformation is reflected in the above images of pure SEES and its SEES/oil = 60 40 composition. The loading leads to an increase of the structural factor from 21 to 53 nm. Therefore, the incorporation of oil to ethylene-butylene blocks induced larger separation of micelles formed predominantly by styrene blocks. 

By swelling with aqueous electrolyte, cations (and, to lesser extent, also anions) penetrate together with water into the hydrophilic regions and form spherical electrolyte clusters with micellar morphology. The inner surface of clusters and channels is composed of a double layer of the immobilized —SO3 groups and the equivalent number of counterions, M+. Anions in the interior of the clusters are shielded from the —SOJ groups by hydrated cations and water molecules. On the other hand, anions are thus... 

Selected examples of block copolymer micelles in both aqueous and organic media will then be presented in Sects. 3 and 4. Section 4.3 emphasizes stimulus-responsive micellar systems from double-hydrophilic block copolymers. Prediction of the dimensional characteristic features of block copolymer micelles and how it varies with the composition of the copolymers will be shortly outlined in Sect. 5, with a consideration of both the theoretical and experimental approaches. Tuning of micellar morphology and triggering transitions between different morphologies will then be discussed in Sect. 6. 

Eisenberg and coworkers have pioneered the field of micellar morphology control with the so-called crew-cut micelles. Generalities about the structure and preparation of crew-cut micelles have been described in Sects. 2.2,... 

Minatti E, Viville P et al (2003) Micellar morphological changes promoted by cyclization of PS-b-PI copolymer DLS and AFM experiments. Macromolecules 36 4125-4133... 

Massey JA, Temple K et al (2000) Self-assembly of organometallic block copolymers the role of crystallinity of the core-forming polyferrocene block in the micellar morphologies formed by poly(ferrocenylsilane-b-dimethylsiloxane) in n-alkane solvents. J Am Chem Soc 122 11577-11584... 

Fig. 42. Theoretical phase diagram for diblock copolymers in the weak segregation limit The left side shows the mean field result of LeiUer [43], the right side the theory of Fredrickson and Jfelfand [58] which includes fluctuation corrections, for an effective degree of polymerization N = 104. LAM, Hex, BCC denote the various mesophases lamellar, hexagonal (Le., cylindrical morphology) and body-centered cubic (i.e., spherical micellar morphology). From Bates and Fredrickson (39)...

The influence of micellar morphology on the exchange kinetics in diblock copolymer micelles has been investigated by Lund et al. [104]. The studied system was a short chain PEPl-PEOl copolymer with symmetric block composition in water/ DMF mixtures as selective solvents for PEO. The morphological behavior of this system has already been described. The main features are illustrated in Eig. 20d. 

Aside from block copolymer composition and the quahty of the block-selective solvent, polymer concentration can also affect micellar morphology. For example, the length of cylindrical micelles normally increases with the concentration of diblock copolymers in a block-selective solvent [38-40]. If the aggregates are kinetic products, the morphologies will be affected by sample preparation conditions and history as well. 

The Vilgis and Halperin theory [46] does help shed light on the possible different morphological behaviors of micelles of coU-coU and crystalline-coil diblock copolymers. It can not be used to predict quantitatively the copolymer compositions at which the different micellar morphological transitions take place, because only scaling relations and not quantitative relations were derived for the free energies of three types of micelles. Aside from the semi-quantitative nature of the free energy expressions, the theory did not discuss tubular micelles at alL It examined only hairy disks, star-like micelles with a cubic core, and cylindrical micelles with a cubic-prism-shaped core. 

For rod-coil diblock and coil-rod-coil triblock copolymers 53 the effects of micellar morphologies on the photophysical properties were studied by optical absorption (UV-Vis) and PL. The experimental results showed that the diblock PF-b-PlVP (53a) maintained spherical micellar aggregates as the MeOH content increased. The triblock 53b was found to readily aggregate in elongated cylinders due to its symmetric structure (Figure 22). The quantum efficiencies were gradually quenched with increasing MeOH content for both copolymers. 

This chapter is focused on spherical particles (micelles and vesicles) but should highlight that there has been increased recent interest in the preparation of cylindrical particles. This is due to recent realization of their advantages in comparison to spherical micellar morphologies with preferable properties being elicited in their application as templates for spherical micelles and nanowires as... 

Micelles from AB and ABC block copolymers in organic and aqueous solvents preparation, control of micellar morphology new trends in the field... 

A brief inspection of Fig. 5 reveals that these supramolecular structures could be similar to those self-assembled from block copolymers. Two major differences exist between self-assembling dendrons and block copolymers. First, all structures in Fig. 4 are generated from the same chemical composition but different primary structure, including constitutional isomeric primary structures, and secmid, they exhibit intramolecular order. Block copolymers provide micellar morphologies with different stractures determined by different ratios between their dissimilar segments. 

Other micellar morphologies, such as slightly elliptic, rod-like, vesicles, crew-cut micelles, flower-like micelles, etc were reported more recently by different authors [126, 127]. 

Table 1 M, PDI, Block Ratio, and Micellar Morphology for PFP-h-PFS-h-PDMS Triblock...

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