Composites lamellar structures

With diblock copolymers, similar behavior is also observed. One component is enriched at the surface and depending on miscibility and composition a surface-induced ordered lamellar structure normal to the surface may be formed. Recent investigations include poly (urethanes) [111], poly(methoxy poly (ethyleneglycol) methacrylate)/PS [112] and PS/PMMA [113, 114]. In particular the last case has been extensively studied by various techniques including XPS, SIMS, NR and optical interferometry. PS is enriched at the surface depending on blockcopolymer composition and temperature. A well ordered lamellar structure normal to the surface is found under favourable conditions. Another example is shown in Fig. 6 where the enrichment of poly(paramethylstyrene), PMS(H), in a thin film of a di-... 

Weakly segregated systems, Todt > Tc > Tg with soft confinement. In this case, crystallization often occurs with little morphological constraint, enabling a breakout from the ordered melt MD structure and the crystallization overwrites any previous melt structure, usually forming lamellar structures and, in many cases, spherulites depending on the composition [10-18],... 

Figure 1. Powder XRD diagrams of mesostructured alumi nophosphate / surfactant composite materials prepared in (a) water (120°C), (b) ethanol (90°C), (c) methanol (25°C), (d) ethanol (10°C). Lamellar and hexagonal phases are indexed "4" corresponds to a phase with presumably lamellar structure.

The resulting phase diagram for diblock copolymers is shown in Fig. 2.40.The theory predicts that microphase separation occurs to a body-centred cubic structure for all compositions except where a direct second-order transition to a lamellar structure is predicted. First-order transitions to hex and lam phases are expected on further lowering the temperature for asymmetric diblocks. 

Crystallization in asymmetric diblocks with compositions = 0.35 and 0.46 was also investigated by Hamley et al. (19966). It was found that a lamellar structure melted epitaxially (i.e. the domain spacing and orientation were maintained across the transition) to a hexagonal-packed cylinder structure in the /PE = 0.35 sample. This is illustrated in Fig. 5.15, which shows SAXS patterns in the solid and melt states, with a schematic of the epitaxial melting process (Hamley et al. 1996a.b). The same epitaxial transition has been observed for a polyethylene oxide)-poly(buty)ene oxide) diblock (Ryan et at. 1997) vide infra). 

Ia-3d), 32 and MCM-50 (with a lamellar structure, space group p2), where MCM stands for Mobile Composition of Matter (Fig. 3.3). 33... 

Figure 21.2 Assembly of mesosfructured hybrids, (a) Nanoparticles smaller than the darker gray block s R0 are miscible and assemble into a lamellar structure, (b) Nanoparticles larger than the darker gray block s R0 segregate, forming a nanoparticle-rich core around which lamellae assemble into an onion-type structure, (c) This can be used to generate compositionally heterogeneous nanostructures from tailored nanoparticle size distributions.10 (Reprinted with permission from S. C. Warren et al., Nature Mater. 2007, 6, 156-161. Copyright 2007 Macmillan Publishers Ltd.)...

Teyssie and coworkers [86] studied the effect of macromolecular architecture on the lamellar structure of the poly(ethylene oxide) crystallizable arms in (poly tert-butyl styrene)(poly(ethylene oxide))2 [PtBuS(PEO)2] miktoarm stars by using SAXS and differential scanning calorimetry (DSC). The results were compared with the ones obtained on poly(tBuS-fe-EO) materials. At the same total molecular weight and composition the melting temperature, the degree of crystallinity and the number of folds of PEO chains were found to be lower for the branched samples. 

The comparison of copolymers SB, BMS and BVN with the same compositions and molecular weight and exhibiting all a lamellar structure has shown that the extension of the macromolecular chains depends upon the nature of the nonpolybutadiene blocks. The extension of the chains increases in the order styrene, a-methylstyrene, vinylnaphtalene and the extension of the polybutadiene chain is caused by that of the adjoined chain85. ... 

Five fundamental domain structures are possible for block copolymers consisting of two types of blocks. Generally lamellar structures will form at compositions with approximately equal proportions of the two components. As the proportion of one component increases at the expense of the other, cylindrical morphologies will result. The matrix phase will... 

The observation that broad, bimodal styrene, block length distributions tend to favor continuity of the polybutadiene phase is not confined to 75% styrene content. Thus, a limited study at 50% styrene showed that polybutadiene-continuous compositions could be prepared by broad blending in place of the normal alternating lamellar structures characteristic of this composition. 

In the early stages of bone formation, the osteons dominate the bone structure to make an overall structure of fiber-matrix composite. While the primary bone has a dense structure, the secondary bone structure is this composite. As a result, the cortical bone structure becomes very complex. It is microscopically porous, has a lamellar structure, and is also a fiber-matrix composite. Size and packing of osteons and canals, and their orientation, determine the mechanical properties of these bones. 

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