Core-shell cylinder structure

Fig. 28 SEM images of about 60 nm thick films of SVT block terpolymers along with expected structural elements of the thin-film structure, (a) Core-shell cylinders (b) helices wound around a cylindrical core (c) (112) plane of an ideal double gyroid structure. Copyright (2002) Wiley. Used with permission from [18]...

Abstract Polyelectrolyte block copolymers form micelles and vesicles in aqueous solutions. Micelle formation and micellar structure depends on various parameters like block lengths, salt concentration, pH, and solvent quality. The synthesis and properties of more complicated block and micellar architectures such as triblock- and graft copolymers, Janus micelles, and core-shell cylinder brushes are reviewed as well. Investigations reveal details of the interactions of polyelectrolyte layers and electro-steric stabilization forces. 

There have been only few reports on nanotube formation from the self-assembly in block-selective solvents of copolymers consisting of only coiled blocks. Since nature abhors vacuum, the spontaneous formation of tubular structures from block copolymers in bulk has not been reported and is probably impossible. While the direct preparation of block copolymer nanotubes by self-assembly has been so far difficult, it has been relatively easy to prepare cylindrical nanoaggregates or micelles from ABC triblock copolymers in selective solvents for A only. In such aggregates or micelles, the A block comprises the corona and the C and B blocks comprise the core/shell cylinders. In bulk at the right triblock copolymer composition, the different blocks of an ABC triblock copolymer segregate predictably into C and B core/shell cylinders dispersed in the A matrix [50,51], if the interfacial tension between the A and C blocks are comparable to that between the A and B blocks and that... 

The appearance and persistence of core-shell structures as well as the occurrence of phase separation are attributed to a small asymmetry in the X -parameters (xPS-pi = 0.06, xpi-pdms = 0.09 and xps-pdms = 0.20). Hence, a PDMS core surrounded by a PI shell embedded in a PS matrix results in a smaller inner diameter interfacial area, relative to that for the PS-PI case. In a blend of a PS-fo-PI-fc-PDMS triblock with PS and PDMS homopolymers, more PS homopolymer is expected to be found in the corona of the PS block than PDMS homopolymer in the corona of the PDMS block because the penalty for contact between the PI block and PDMS homopolymer is larger. In consequence, the distribution of homopolymers favours an expanded PS-PI interface, making the core-shell morphologies, gyroid and cylinder, more prevalent. 

Fig. 2.26 TEM from a poly(2-vinylpyridine)-poly(isoprene)- poly(styrene) ABC triblock copolymer, showing a hexagonal cylinder core-shell structure (Gidcma/. 1993).The light, grey and black regions correspond to the PS, P2VP and PI respectively in sections (a) perpendicular and (b) parallel to the rod direction.

Fig. 63 X-shaped quaternary bolaamphiphile 189 forming hexagonal cylinder phases with models showing (a) the three-color, (b) two-color and (c) single color hexagon tiling patterns in the left bottom comer the core-shell structure of the mixed cells is illustrated dark = Rp-chains white = Rsi-chains gray = mixed cells [42]...

Starblock (or radial star) copolymers form another kind of amphiphilic nanoparticles which can be regarded as unimolecular micelles. Alternatively, cylindrical core-shell brushes can be regarded as unimolecular cylinder micelles. Due to the covalent attachment of the block copolymers at one end, frustrated micellar structures can be made which would never form spontaneously. The cylindrical systems will be reviewed in Sect. 4.2. 

Also block copolymers with more than three components have been studied. In principle, such systems can show more complex structures than the ones presented so far. A first systematic study has been published for tetrablock quaterpolymers, that are linear block copolymers with four chemically different blocks. In this case core-shell shell matrix morphologies analogous to the spheres, cylinders, and double gyroid known for diblock copolymers and lamellae (compare with Eigure 1) were found [170,171]. As a nice example, in Figure 13 core-shell shell cylinders are shown. 

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