Domain orientation

Figure 13.22 Hormone-receptor interactions involving the domain-domain linker region in the receptor, (a) Interactions between the growth hormone (red) and the growth hormone receptor (blue) linker region. Glu 127 of the receptor forms a salt bridge to Arg 167 in the hormone, (b) The same interaction area in the growth hormone (red)-prolactin receptor (green) complex. The displacement of the linker region due to differences in the domain orientations have brought Asp 124 in the prolactin receptor into contact with Arg 167 of the hormone. (Adapted from W. Somers et al.. Nature 372 478-481, 1994.)...

However, a PS-fo-PI/PI blend shows direct L G transitions without appearance of the PL phase. The L microdomain is more favourable than the PL phase since the volume fraction of the PI block component and the symmetry of microdomains is increased by the addition of PI homopolymer. Hence, the PL phase may not be formed as an intermediate structure if relatively high molecular weight PI homopolymer is added. The latter is not able to effectively fill the corners of the Wigner-Seitz cells in consequence packing frustration cannot be released and the PL phase is not favoured [152]. In contrast, the addition of low molecular weight PI homopolymer to the minor component of the PL phase reduces the packing frustration imposed on the block copolymers and stabilizes it [153]. Hence, transition from the PL to the G phase indicates an epitaxial relationship between the two structures, while the direct transition between L and G yields a polydomain structure indicative of epitaxial mismatches in domain orientations [152]. 

A basic kit of components can be defined to which you can add components that are more domain-oriented. The following is a selection of basic pieces that can be used in many ways. It s intended to provide a general flavor of what can be achieved. 

The self-assembly of block polymers, in the bulk, thin film and solution states, produces uniformly sized nanostructured patterns that are very useful for nanofabrication. Optimal utilization of these nanoscopic patterns requires complete spatial and orientational control of the microdomains. However, the microdomains in the bulk state normally have grain sizes in the submicron range and have random orientations. In block copolymer thin films, the natural domain orientations are generally not desirable for nanofabrication. In particular, for composition-asymmetric cylindrical thin films, experimental... 

Fig. 5 Schematic cross-sections of thin film morphologies of the topographic pattern grown by a graphoepitaxy method. A micropattern with different lamellar domain orientation is shown, a Surface-parallel lamellae, typical of film thickness t greater than the natural equilibrium period Lq. b Surface-perpendicular lamellae, typical of film thickness t less than L0. (adapted from [41])...

Fig. 6 Illustration of surface energy effects on the self-assembly of thin films of volume symmetric diblock copolymer (a). Sections b and c show surface-parallel block domains orientation that occur when one block preferentially wets the substrate. Symmetric wetting (b) occurs when the substrate and free surface favor interactions with one block B, which is more hydrophobic. Asymmetric wetting (c) occurs when blocks A and B are favored by the substrate and free surface, respectively. For some systems, a neutral substrate surface energy, which favors neither block, results in a self-assembled domains oriented perpendicular to the film plane (d). Lo is the equilibrium length-scale of pattern formation in the diblock system...

Recently, significant advances have been made in controlling the micro domain orientation in diblock copolymer films [10,11,270-284]. When the copolymer is placed between two solid interfaces, the morphology responds strongly to the deviation of the film thickness from the integer number of the layers [271-274]. By adjusting the chemical structure of the interfaces so that both blocks interact with them equally, perpendicular orientation of the microdomains was... 

Fig. 4. The actin-binding cleft between the upper (red) and lower (gray) 50K domains (orientation as in Fig. 5A). In A (rigor-like), the cleft is shut. In B (pre-powerstroke), the outer end of the cleft (that forms the actin-binding site) is fully open, but the apex or inner end of the cleft (next to the nucleotide-binding pocket ATP is shown in B) is closed. This closure is brought about by the switch 2 element (SW2) being in the closed conformation. In C (post-rigor), both the outer end and the inner end are open. SW2 is open. In A and B the dispositions of SW2 are similar, but not identical. We refer to them as closed 1 (Cj) and closed 2 (C2), respectively.

How many different domain orientations are possible in (A) iron, (B) nickel, and (C) cobalt ... 

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