Sphere-forming block copolymers

Preferential attraction of one of the blocks to the surface brakes the symmetry of the structure and results in layering of microdomains parallel to the surface plane through the entire film thickness. The energetically favored film thicknesses are then quantinized with the characteristic structure period in the bulk through the formation of surface relief structures, also called terrace formation. These structures were established initially for lamella systems [37-39] and later for cylinder- [40-43] and sphere-forming block copolymers. 

Lee, S., Bluemle, M. J., and Bates, F. S. (2010). Discovery of a Frank-Kasper o phase in sphere-forming block copolymer melts. Science 330, 349-353. 

Dormidontova EE, Lodge TP (2001) The order-disorder transition and the disordered micelle regime in sphere-forming block copolymer melts. Macromolecules 34 9143-9155 Matsen MW (2002) The standard Gaussian model for block copolymer melts. J Phys Condens Matter 44 R21-R47... 

Wang J, Wang ZG, Yang Y (2005) Nature of disordered micelles in sphere-forming block copolymer melts. Macromolecules 38 1979-1988... 

From the results given above, three cases can be considered (1) percolated systems where the crystallizable block is not in isolated MDs as most of the lamellar forming block copolymers (Avrami indices >2) (2) block copolymers that form cylinders within an amorphous matrix, which can be considered an intermediate case since it could contain a fraction of percolated cylinders and a fraction of isolated cylinders therefore, its fractionated crystallization process will be a reflection of the mixture of these two crystal populations (Avrami indices between 1 and 2) and (3) systems with isolated MDs that can be exemplified by spheres within an amorphous matrix. In this case the overall crystallization kinetics will be dominated by primary nucleation since the growth within such nano-droplets can be considered instantaneous (Avrami indices around 1 or lower). Table 12.3 shows a compilation on the Avrami index values obtained for several systems, and the data on this table are in agreement with the three cases we have just explained. 

Finally, block copolymers have been made in a two-step process. First a mixture of chloroprene and -xylenebis-Ai,Ar-diethyldithiocarbamate is photopolymerized to form a dithiocarbamate terminated polymer which is then photopolymerized with styrene to give the block copolymer. The block copolymer has the expected morphology, spheres of polystyrene domains in a polychloroprene matrix (46). 

As these block copolymers were synthesized using the anionic polymerization technique, their molecular weight distributions were narrow. The microspheres with narrower size distribution are better for well-ordered self-organization. Actually, all block copolymers synthesized for these works formed poly(4-vinyl pyridine) (P4VP) spheres in the PS matrices with narrow size distributions. 

The morphology of the ABA-type linear block copolymers is strongly influenced by the volume fraction of the two components. For example, in PS-EB-PS-type block copolymer as the volume fraction of PS is increased, the shape of the dispersed PS phase changes from spherical (comprising body-centered cubic spheres of PS dispersed in continuous soft phase) to cylindrical form (hexagonal packed cylinders of PS) [10,133,134]. When the volume fraction of the two phases... 

Further modification of the above nanostructures is useful for obtaining new functional materials. Thirdly, we apply the dopant-induced laser ablation technique to site-selectively doped thin diblock copolymer films with spheres (sea-island), cylinders (hole-network), and wormlike structures on the nanoscale [19, 20]. When the dye-doped component parts are ablated away by laser light, the films are modified selectively. Concerning the laser ablation of diblock copolymer films, Lengl et al. carried out the excimer laser ablation of diblock copolymer monolayer films, forming spherical micelles loaded with an Au salt to obtain metallic Au nanodots [21]. They used the laser ablation to remove the polymer matrix. In our experiment, however, the laser ablation is used to remove one component of block copolymers. Thereby, we can expect to obtain new functional materials with novel nanostmctures. 

Figure 5.10 Self-organization of di-block copolymers. Block copolymers can form spherical and cylindrical micelles, vesicles, spheres with face-centered cubic (fee) and body-centered cubic (bcc) packing, hexagonally packed cylinders (hex) minimal surfaces (gyroid, F surface, and P surface), simple lamellae and modulated and perforated lamellae. (Adapted from Bucknall and Anderson, 2003.)...

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