Oriented lamellar morphologies

Ueda et al. [26] recently investigated a flow-oriented PE-fr-aPP diblock copolymer with Mw = 113 000 (Mn/Mw = 1.1) and a PE volume fraction of 0.48. This diblock copolymer is in the strong segregation regime (i.e., estimated xN = 10.5 and Todt = 290 °C) and has a lamellar morphology in the melt. They found a breakout phenomenon with the formation of spherulites in an intermediate crystallization temperature range 95 < Tc < 101 °C. At crystallization temperatures above 101 °C or below 95 °C spherulites were not formed and the crystallization was confined within the lamellar MD. Ueda et al. report that lamellar MD and spherulites do not co-exist when the material crystallizes from the melt which is separated in lamellar MDs. In other words, in this particular case, breakout or confined crystallization within lamellar MDs depends on the crystallization conditions. 

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])...

As discussed below, the quality of the alignment (and even its direction in the case of lamellar morphology), is influenced by temperature, as well as the frequency and strain amplitude of the aligning shear field. No general theory for the alignment of block-copolymer phases has yet been developed. However, studies of a number of different block-copolymer systems show that in ordered states with cylindrical domains, shear orients the cylinders parallel to the flow, while for lamallar microdomains, two different shear-induced orientations are commonly found, depending on alignment conditions in both of these orientations, the flow direction lies in the plane of the lamellae. 

Recent studies in the fine structures of radiation polymerized PTOX show that they are disordered crystals in which maln-crystal-lites and sub-crystallites are arranged in series (7)- The fine structures of PTEOX are even more disordered and complex than those of PTOX, and are believed to possess an oriented lamellar morphology. However, when the post-polymerization is carried out at temperatures above 90 C, the sub-crystallites disappear. WAXS studies indicate that the (009) and (0018) reflections of PTEOX have an asymmetrical profile, suggesting the existence of two different lattice spacings along the fiber axis. Odajima, et al. (8) suggested that there may be two kinds of crystallites present, namely those with the extended fibrillar and the folded lamellar morphologies. 

Other LC-based copolymers incorporating styrene-based monomers were prepared by Ober et al. [149] who chain extended pAcOSt-TEMPO (Mn=7000, Mw/Mn=1.18) with [(4 -methoxyphenyl)4-oxybenzoate]-6-hexyl (4-vinylbenzoate) (MPVB, Fig. 10). The reactions were controlled, with molecular weights ranging from Mn=12,600-23,000 and Mw/Mn=1.19-1.44. The content of pMPVB in the copolymer determined by XH NMR increased as the molar ratio of the MPVB to pAcOSt-TEMPO increased [149]. For two out of the three copolymers prepared a smectic-isotropic transition was observed however, it was at a value lower than expected based on the composition of the copolymer, even after annealing. X-Ray diffraction patterning indicated that the copolymer was oriented in a lamellar morphology and that the smectic layers were perpendicular to the block copolymer lamellae [149]. 

The cross-linking of poly(oxyethylenes) with polymerizable, hydrophobic endgroups within oriented lamellar phases of the ternary system f iz s/de-cane/water was reported by Meier [73]. After cross-linking oriented polymer gels were obtained that retained their lamellar morphology after extraction of the template, and which showed one-dimensional swelHng by water. 

Figure 12.17. Magnetically induced alignment of microphase-separated nanostructures in PS-based azo LCBCs. All the PS nanocylinders were oriented along the magnetic field, which shows no effect on the lamellar morphologies. Source Reproduced with modifications from Tomikawa et al., 2005.

The morphology for a thin copolymer film is shown in Fig. 6 before and after microphase separation, viewed through one of the repulsive surfaces. Perpendicular orientation of lamellae is clearly obtained near the reflecting and neutral surfaces. On the other hand, orientation is not perfect and the long-range order of the two-dimensional lamellar morphology at the surface is highly disturbed by defects, see Fig. 6. 

A very full investigation of the deformation mechanisms in material with parallel lamellar morphology has recently been published by Ladizesky and Ward. (The authors remark that the tensile data of Owen and Ward are not in accord with their own measurements, almost certainly because of errors of temperature measurement in the earlier experiment.) Data have been interpreted in terms of a model of perfect parallel lamellae, with no spread of orientation, separated by isotropic amorphous regions. It was concluded that the main deformation mechanisms were an inter-lamellar pure shear, and a highly time-dependent intra-lamellar c-shear, which significantly affected the values of S22 Rnd Ss5-... 

Figure 8.4 SAXS patterns of oriented lamellar morphologies in the system SI52C3E5I.6/D4 at 58 C (a) Azimuthally averaged scattering intensity, after background correction from bottom to top (poA = 0, 0.05, 0.05, 0.10, 0.16, 0.15, 0.15, 0.15, and 0.20, scaling factor -5 with respect...

Fig. 5.12 Schematic of the surface-ordering process in a diblock copolymer. The top diagram shows the dibiock copolymer in a phase mixed state. This is not accessible for PS/PMMA co-polymers via solvent-casting processes. The center diagram corresponds to a microphase-separated morphology where the periodic lamellar microdomains are randomly oriented in the specimen. After annealing for 24 h at 170 °C, the copolymer exhibits a lamellae morphology oriented parallel to the surface as shown in the bottom picture. Reprinted with permission from ref. [96]...

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