Polyelectrolyte micelles

Spectacular increases in spontaneous and base-catalyzed or metal-assisted aquation rate constants of particularly pentaammineco-balt(III) complexes have been observed in the presence of polyelectrolytes and micelles. Polyelectrolytes are known to cause marked acceleration of reactions, though decelerations can be observed, and the effects are very large compared with those produced by equivalent amounts of corresponding low molecular weight substances similar effects are observed in solutions containing charged micelles. This area of research has been extensively reviewed (63,101,133,139,195, 206, 207), so discussion will be selective. 

Keywords Amphiphilic block copolymers Micelles Polyelectrolytes Polymorphism Self-assembly... 

Keywords Co-assembly Cylindrical polyelectrolyte brushes Interpolyelectrolyte complexes Ionic amphiphilic block copolymers Micelles Polyelectrolytes Star-shaped polyelectrolytes... 

Keywords Coacervate Co-assembly Janus Micelle Polyelectrolyte Polymer Scattering Segregation Self-assembly Self-consistent field calculations... 

Keywords Complex coacervate Coordination polymers Layer-by-layer Micelles Polyelectrolytes Self-assembly Supramolecular polymers... 

Functionalized polyelectrolytes are promising candidates for photoinduced ET reaction systems. In recent years, much attention has been focused on modifying the photophysical and photochemical processes by use of polyelectrolyte systems, because dramatic effects are often brought about by the interfacial electrostatic potential and/or the existence of microphase structures in such systems [10, 11], A characteristic feature of polymers as reaction media, in general, lies in the potential that they make a wider variety of molecular designs possible than the conventional organized molecular assemblies such as surfactant micelles and vesicles. From a practical point of view, polymer systems have a potential advantage in that polymers per se can form film and may be assembled into a variety of devices and systems with ease. 

The pioneering work on amphiphilic polyelectrolytes goes back to 1951, when Strauss et al. [25] first synthesized amphiphilic polycations by quaternization of poly(2-vinylpyridine) with n-dodecyl bromide. They revealed that the long alkyl side chains attached to partially quaternized poly(vinylpyridine)s tended to aggregate in aqueous solution so that the polymers assumed a compact conformation when the mole fraction of the hydrophobic side chains exceeded a certain critical value. Thus, Strauss et al. became the first to show experimentally the intramolecular micellation of amphiphilic polymers and the existence of a critical content of hydrophobic residues which may be compared to the critical micelle concentration of ordinary surfactants. They called such amphiphilic polyelectrolytes polysoaps [25],... 

As has been described in Chapter 4, random copolymers of styrene (St) and 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) form a micelle-like microphase structure in aqueous solution [29]. The intramolecular hydrophobic aggregation of the St residues occurs when the St content in the copolymer is higher than ca. 50 mol%. When a small mole fraction of the phenanthrene (Phen) residues is covalently incorporated into such an amphiphilic polyelectrolyte, the Phen residues are hydrophobically encapsulated in the aggregate of the St residues. This kind of polymer system (poly(A/St/Phen), 29) can be prepared by free radical ter-polymerization of AMPS, St, and a small mole fraction of 9-vinylphenanthrene [119]. 

In the presence of the polyelectrolyte polyallylamine hydrochloride (PAAN), the formation of a pearl-necklace structure between AOT-reversed micelles and PAAN was... 

Other examples of organized molecular assemblies of interest for photocatalysis are (1) PC-A, PC-D or D-PC-A molecules where PC, A and D fragments are separated by rigid bridges (2) host-guest complexes (3) micelles and microemulsions (4) surfactant monolayers or bilayers attached to solid surfaces, and (5) polyelectrolytes [19]. 

Interpolyelectrolyte complexes Micelles Nanostructures Polyelectrolytes Supramolecular chemistry... 

Riess [14], while polyelectrolyte block micelles have been surveyed by Forster et al. [15],... 

Block copolymer micelles with a polyelectrolyte corona are a very important class of colloidal particles in aqueous medium and are often referred to as polyelectrolyte block copolymer micelles. The micellization behavior of these charged micelles has been very recently reviewed by Riess [14] and FOrster et al. [15]. A brief overview of the topic will therefore be presented in what follows. Amphiphilic block copolymers consisting of one hydrophobic block linked to one ionic block will only be discussed in this section. Blocks copolymers containing one hydrophilic block and one ionic block will be discussed in Sect. 4.3. 

The interest in these block copolymer micelles arises from the polyelectrolyte coronal block whose intrinsic properties are strongly influenced by many parameters including pH, salt concentration, and polar interactions. Moreover, they provide a unique model to mimic polyelectrolyte brushes at a high segment concentration, as noted by Forster [15]. 

Typical examples of polyelectrolyte micelles have been reported for cationic PS-P4VPQ and for other quaternized P2VP- or P4VP-containing block copolymers by Selb and Gallot [142,143]. Eisenberg et al. [144-147] and Tuzar and coworkers [41,148] have studied the PS-PAA and PS-MAA systems in their acidic or neutralized anionic form. Typical polyelectrolyte behavior was detected for these types of micelles. 

As exemplified above, most of the studies on anionic polyelectrolyte block copolymer micelles have been carried out on P(M)AA-containing copolymers. The ionization degree of these anionic blocks is strongly dependent on... 

Fig. 8 Cryo-TEM image of aqueous PB-P2VPQ micelles showing filament network of polyelectrolyte chain bundles. Scale bar is 50 nm. Reprinted with permission from [15]. Copyright (2004) Springer...

Ordered body-centered cubic structures were observed by shearing aqueous gels made from anionic PtBS-PMANa block copolymer micelles [163]. The emergence of the ordered gel state could be accounted for similar building up of a polyelectrolyte-based fibrillar network that can be oriented under shear. 

Salt effects in polyelectrolyte block copolymer micelles are particularly pronounced because the polyelectrolyte chains are closely assembled in the micellar shell [217]. The situation is quite reminiscent of tethered polymer brushes, to which polyelectrolyte block copolymer micelles have been compared, as summarized in the review of Forster [15]. The analogy to polyelectrolyte brushes was investigated by Guenoun in the study of the behavior of a free-standing film drawn from a PtBS-PSSNa-solution [218] and by Hari-haran et al., who studied the absorbed layer thickness of PtBS-PSSNa block copolymers onto latex particles [219,220]. When the salt concentration exceeded a certain limit, a weak decrease in the layer thickness with increasing salt concentration was observed. Similar results have been obtained by Tauer et al. on electrosterically stabilized latex particles [221]. 

Charged polysoaps (polymer micelles) combine within a molecule structural characteristics of the conventional micelles and polyelectrolytes, and supposedly adopt globular conformations in aqueous media with the hydrophobic region inside and charged groups outside as in water-soluble proteins. Thus,... 

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