Cylindrical Microdomains

the hexagonal phase is suppressed. These peculiar observations suggest that near Todt the hexagonal phase is especially delicate, and its free energy is only very slightly less than that of the disordered state. 

As with lamellae-forming samples, when the hexagonal phase forms after a quench from the disordered state, terminal behavior in G and G is replaced by nonterminal behavior (see Fig. 13-13). For hexagonal cylinders, the low-frequency behavior is generally more elastic than for lamellae the apparent power-law exponent in G oc tu is usually somewhat lower (n 0.0-0.4) for the former than for the latter (n 0.5) (Gouinlock and Porter 1977 Morrison et al. 1990 Winter et al. 1993 Almdal et al. 1992). This is perhaps not surprising, since ordered hexagonal cylinders are solid-like (i.c., positionally ordered) in two dimensions and lamellae are positionally ordered in only one. 

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The surface of bulk block copolymer samples has been studied using TEM by Turturro et al. (1995). They report that non-equilibrium structures with lamellar and cylindrical microdomains oriented normal to the free surface can result from solvent casting, with a high evaporation rate. However, slower evaporation of solvent from their PS-PB diblocks resulted in the equilibrium conformation with domains parallel to the free surface. Perpendicular orientation of PS-PB lamellae at the free surface was observed earlier by Henkee et al. (1988) who studied thin films prepared by solvent casting. They observed that a reduction of this orientation occurs in favour of the parallel one on annealing the sample. 

Fig. 4 (a) SFM phase image (3x1.5 im) of the surface structures in SB47 films annealed in vacuum at 120°C. The white contour lines are taken from the height image (not shown) and mark the borders between the flat regions, as well as the transition region between the indicated terraces, (b) Spacings of cylindrical microdomains as a function of the local film thickness... 

In order to account for the real 3D structure of cylindrical microdomains, we denote the configurations in Fig. 22a, e and c, g as cylinder-phase defects (cyl-dislocation and +1/2 cyl-disclination), and the configurations in Fig. 22b,f and d,h as matrix defects (m-dislocation and m-disclination). In our systems, cyl-dislocations generally develop during the early stages of film annealing when the overall defect density is high. In well-equilibrated films, cyl-dislocations are less frequent as compared to m-dislocations. 

Floudas and coworkers [88] investigated the static and kinetic aspects of the order-disorder transition in SI2 and SIB miktoarm stars using SAXS and rheology. At temperatures above the order-disorder transition (ODT) the mean field theory describes the experimental results quite well. Near the ODT, SAXS profiles gave evidence for the existence of fluctuations. Both samples separated into cylindrical microdomains below the ODT. The ODT was determined on shear oriented samples and found, by SAXS, to be 379 K in both cases. This was confirmed by rheology. The discontinuities in SAXS peak intensity and in the storage modulus near the ODT were more pronounced for the miktoarm stars than for the diblocks. The %N values, where % is the interaction parameter and N the... 

Arrays of 3 nm diameter cylindrical microdomains oriented normal to the film surface with a center-to-center distance of 6.9 nm are reported. 

The earliest rheological studies on block copolymers were carried out on triblocks with hexagonally ordered cylindrical microdomains (Chung and Gale 1976 Gouinlock and Porter 1977). In these triblocks, the end blocks were much smaller than the center... 

However, from simple packing considerations of layered mesogens in a cylindrical microdomain, we can form two kinds of structures as indicated in Fig. 10. One is ho-... 

An isothermal morphology diagram of poly(styrene-fe/oc -butadiene) is shown in Fig. 19 as a function of molecular weight and copolymer composition the classic morphologies include spherical microdomains (0< a<0.15) packed in a body-centered cubic lattice, hexagonally packed cylindrical microdomains (0.15 <( a-0-3), and alternating lamellae of approximately symmetric diblocks (0.3 <0 -0-5). Sever-... 

FIGURE 13.6 TEM of cylindrical microdomains in extruded and annealed SBS sample where the micrograph was taken perpendicular to the extrusion direction. An electron micrograph taken parallel to the extrusion direction had a striated stmcttrre (from Dlugosz et al., 1970). 

Tokita M, Adachi M, Takazawa F, Watanabe J. 2006. Shear flow orientation of cylindrical microdomain in liquid crystalline diblock copolymer and its potentiality as anchoring substrate for nematic mesogens. Jpn J Appl Phys 45 9152 9156. 

Investigations on the self-assembly in thin films of an amorphous P2VP-PS-P2VP triblock copolymer, forming cylindrical microdomains in bulk, showed that the orientation of microdomains due to the P2VP/substrate interactions persisted in the entire film in contrast to the diblock case [14], This was viewed as a result of the formation of an interconnected structure in the triblock coming from the formation of loops within the microdomains. More recently, AFM and SAKS measurements on a PEO-PBO-PEO amorphous-semicrystalline triblock thin film revealed the presence of a semicrystaUine PEO monolayer at the substrate, comprised of unfolded chains, and PBO blocks at the air/polymer siuface in a looped conformation (15]. 

Polymeric cylinders, as analogs of CPBs, are prepared by the self-assembly of block copolymers. They process a rather rigid (crosslinked or crystalline) cylindrical microdomain as the backbone from which side chains are tethered. These... 

For instance, order-disorder transitions of BCP blends (typically related to macrophase separation processes) in thin films have been studied by Jeong et al. [48]. They used mixtures of PS-b-PMMA having PMMA cylindrical microdomains with homopolymers of either PMMA or poly(ethylene oxide) (PEO) and studied the morphological transitions and the formation of macrophase-separated domains in thin films (Fig. 6.7). Whereas the microdomains in all thin films are oriented perpendicular to the film surface, they found that the miscibility between PMMA homopolymer and PMMA block in thin film was enhanced compared with that in bulk at a given molecular weight of PMMA homopolymer. Equally, the PMMA homopolymer chains in thin films were more localized to the center of PMMA microdomains than in the bulk, which results in a larger increase of the lattice spacing (D) in the former. 

They observed cylindrical microdomains upon microphase separation of the BCR However, addition of the homopolymer modified both the diameter and spacing of the moieties whereas the spatial order and orientation remains. Selective removal of the PMMA either from the BCR or both from BCR and homopolymer leads to pores with two distinct pore sizes. Other BCP/homopolymer blends have also been reported to produce hierarchically structured surfaces with two-fold nanometer and micrometer length scales in porous polymer films [42],... 

Figure 6-11. T smisston electron micrographs of gold partide preparation in hexagonal packed cylindrical microdomains of phase separated norbornenyl phosphine/gold complex copolymCTs a) before and b) after gold particle formation. (Bar = 100 nm in a) 50 nm in b) reproduced by permission from ref. [155J.)...

A field of 37 kV/cm was applied to the film at 250°C for 24 h. Orientation of the cylindrical microdomains, examined in two locations, is shown in Fig. 30. The cylinders follow the field lines in the region where the field was strong ( 37 kV/ cm) and the alignment diminishes in regions where the field strength is smaller... 

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