Fibril bundles

Crown ether binaphthyl derivatives 128-131 (Scheme 71) were synthesized and investigated by Akagi [139], Compounds 128-131 were used to induce chiral nematic phases (N ) in liquid crystals. It was found that the helical twisting power increased with decreasing ring size. Helical polyacetylenes were synthesized in the N phases. It was found that the interdistance between the fibril bundles of the helical polyacetylene was equal to the half-helical pitch of the N liquid... 

In mature tendon, collagen fibril bundles (fibers) have diameters between 1 and 300 mm and fibrils have diameters from 20 to over 280 nm (Figure 3.28). The presence of a crimp pattern in the collagen fibers has been established for rat tail tendon as well as for patellar tendon and anterior cruciate ligament the specific geometry of the pattern, however, differs from tissue to tissue. It is not clear that the crimp morphology of tendon is actually present in tendons that are under normal resting muscular forces. 

Figure 5.12. Lateral fusion of collagen fibrils during fascicle development of chick extensor tendon. Transmission electron micrograph showing the lateral fusion of collagen fibrils at day 17 of chick embryogenesis. Note that the demarcation between collagen fibrils (arrows) is less clear compared to the cross section shown at day 14 (Figure 5.11). Several fibrils appear to be in the process of fusion generating fibrils with irregular cross sections. The fibril bundle (fiber) diameter is still about 2 pm before fusion similar to that observed on day 14 (see Silver et al., 2003).

Carboxymethyl Cellulose (CMC) -In vivo cellulose ribbon formation prevented normal fasciation of fibril bundles into a typical ribbon -Thinner ribbon width and smaller crystallite fibril size -Aggregates and pellicle show birefringence, and contain crossed, superimposed layers of cellulose fibrils oriented in parallel -Less resistant to stress... 

An interesting structure can be found in wood, for example in the different layers of conifer tracheids, where helically arranged cellulose micro-fibril bundles are found (Fig. 9.7). The spiral-Uke lay-up and the angle of the strengthening fibers in the stem walls and of cellulose micro-fibril bundles in the cell walls is optimized according to the types and combinations of... 

Figure 2.12 shows a sehematie representation of the relationship between the twisting degree of the N -LC and the hierarchical morphology of H-PA. In the weakly twisted N -LC, PA fibrils (diameters from 70 to 120mn) are gathered to form fibril bundles (diameters up to 1 pm). Interestingly, the distance between... 

Crystallisation of polymers such as PCL, which crystallise to give spherulitic structures, starts from a nucleus which subdivides at the growth surface to generate a series of very thin (typically 10 nm thick) crystalline lamellae. The lamellae continue to grow and sub-divide to establish the spherically-symmetric structures (spherulites) which consist of a series of crystalline fibrils, bundles of lamellar crystals, extending from the nucleus in all directions, with a constant... 

In many other cases, the nature of the noncova-lent interactions responsible for self-assembly is less clear—however, in general terms, such interactions must exist, and interactions of the gelators in three dimensions must be somehow frustrated by the molecular structures. In this way, fibrillar assembly becomes preferred. However, it should be noted that in addition to simple assembly of a molecular-scale fibril, there must also be some fibril bundling and fiber-fiber interactions, responsible for the formation of a sample-spanning network. These interactions are often relatively poorly understood, although it should be noted that organogelators are very often functionalized with aliphatic chains, which opens the possibility that van der Waals interactions between the hairy surfaces of the fibers, may encourage network formation. 

Figure 12.26. Schematic presentation of the polymer network in a two-scale (fibril-bundle) model showing both the local and macrodirector. The local distribution of fibrils is represented by a square array of polymer fibrils. The relevant distances are also illustrated (from [74]).

This builds an asymmetric reaction field for Ziegler-Natta catalyst which was used for the interfacial polymerization of acetylene. Bundles of PA chains formed fibrils in a PA film, resulting in a hierarchical helical structure. Further, the winding direction could be precisely controlled by selecting the chirality of the chiral dopant. The direction of the twist in the fibril bundles has been found to be opposite to that of the N -LC reaction field. 

However, due to the very high strength of the wood fiber secondary wall, the material resulting from mechanical homogenization of wood fibers also contains a substantial part of larger fibril bundles and even residual fibers and fiber fragments (Figure 8.4). 

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