Lamellar single crystals

Electron diffraction by lamellar, single crystals leads to a two-dimensional, tetragonal unit-cell with a = b = 22.9 A (2.29 nm). From X-ray diffraction data obtained from a film of sedimented, lamellar crystals, it was found that the c axis spacing (7.8 A 780 pm) is equivalent to that in 6-fold and 7-fold amylose helices. The true helical diameters of the 1-butanol, isopropyl alcohol, and 1-naphthol complexes were calculated from experimental data. The ratios of 6 7 8 indicated that the 1-naphthol complex has eight D-glucose residues per turn. The diversity of helical orientations in V-amylose crystals was discussed. 

Lamellar, single crystals of cellulose triacetate, precipitated from nitromethane with butyl alcohol, were studied by X-ray and electron diffraction. Only the crystals containing the mother liquor, or moistened with nitromethane, showed rich diffraction details. From stretched and annealed fibers, it was found that the unit cell is tetragonal, with a = fe = 21.15A (2.115 nm), and c = 41.36 A (4.136 nm). 

Study of the Crystalline Regions. According to our morphological studies, the crystalline structure of UHMWPE pseudo-gel was different under different sample preparations. For example, spherulites and lamellar single crystal stacks were observed when the pseudo-gel was prepared under quiescent conditions, shish-kebab crystals under stirring conditions, and a mixture of single and shish-kebab crystals under uncontrolled conditions (10). 

Lamellar, single crystals of ivory-nut mannan were studied by electron diffraction. The base-plane dimensions of the unit cell are a = 0.722 nm and b = 0.892 nm. The systematic absences confirmed the space group P212121. The diffraction pattern did not change with the crystallization temperature. Oriented crystallization ofD-mannan with its chain axis parallel to the microfibril substrates, Valonia ventricosa and bacterial cellulose, was discovered ( hetero-shish-kebabs ). 

When nitrobenzene alone is used as a solvent (170 C) and with slow cooling, lamellar single crystals are obtained. Their electron diffractograms have an oblique cell (plane group p2). With a mixture of nitrobenzene/decane (65/35) or nitrobenzene/ hexane the dissolution temperature is reduced to about 70 C. 

At about the same time as the papers by Speerschneider and Li, Symons [4,9] described the growth of lamellar single crystals from dispersed PTFE dispersion particles (Fig. 4) and we described thin lamellae on the free surfaces of bulk dispersion PTFE samples (Fig. 5) [4], both prepared by slow cooling fol-... 

Figure 4.11. (a) Schematic representation of a screw dislocation in a lamellar single crystal of PE. The chain direction is [001], (b) Dependence of yield stress cr on crystal thickness ic for crystals of branched PE ( ) and linear PE ( ). The continuous line is calculated from eq. (4.10). (After Young, 1988.)... 

Figure 41. Series of in situ optical micrographs (interference contrast) of /2-C198H398 lamellar single crystals grown from octacosane (initially 2%) at the temperatures indicated. (a—e) extended chain, (f) once-folded chain. Bar length represents 10 //m (from ref 214).

A natural question is why the lamellar single crystal has to deform in a periodic manner. A possible account is due to the induced mechanical field during isothermal crystallization. This periodicity is consistent over the entire crystal and seems to be sensitive to crystallization temperature. The effect of supercooling on the periodicity of undulations obtained in 1 and 2 wt% sPP blend compositions is... 

Figure 2. Shadowed lamellar single crystals of nigeran grown from dilute aqueous solution, the sample was solvent exchanged from water to methanol before...

Figure 5. Schematic of chain organization in lamellar single crystals. The chain folds are shown as regular with adjacent reentry although larger loops at the folds are also a possibility. Based on the known degree of polymerization of the nigeran (ca. 1000—2000 anhydroglu-cose units), the chain orientation in the crystals and crystals dimensions, chain folding must occur (14).

Enzymatic Depolymerization of Lamellar Single Crystals of Nigeran... 

Figure 10-12. Melting behavior of a poly(ethylene) as a function of the morphology and the rate of heating. L, Lamellar single crystals from solution D, dendrites obtained by shock cooling solutions Sq spherulites obtained by shock cooling melts under normal pressures Sc, spherulites produced by crystallization under normal pressures E, extended chain crystals obtained by crystallization from high molar mass Eh and low molar mass Em poly(ethylene) melts under high pressures (after B. Wunderlich).

Miyazaki S, Takahashi K, Shiraki M, Saito T, Tezuka Y, Kasuya K (2000) Properties of a poly(3-hydroxybutyrate) depolymerase from Penicillium funiculosum. J Polym Environ 8 175-182 Mukai K, Yamada K, Doi Y (1992) Extracellular polyhydroxyalkanoate depolymerases and their inhibitor from Pseudomonas lemoignei. Int 1 Biol Macromol 14 235-239 MiiUer B, Jendrossek D (1993) Purification and properties of poly(3-hydroxyvaleric acid) depolymerase from Pseudomonas lemoignei. Appl Microbiol Biotechnol 38 487-492 Murase T, Iwata T, Doi T (2001a) Direct observation of enzymatic degradation behavior of poly[(R)-3-hydroxybutyrate] lamellar single crystals by atomic force microscopy. Macromolecules 34 5848-5853... 

Murase T, Iwata T, Doi Y (2001b) Atomic force microscopy investigation of poly[(R)-3-hydroxy-butyrate] lamellar single crystals relationship between molecular weight tuid enzymatic degradation behavior. Macromol Biosci 1 275-281... 

In 1957, owning to the inventirMi of Ziegler-Natta catalysts to produce sequence-regular polyethylene, Keller prepared the lamellar single crystals of polyethylene from dilute solutions, and observed that the lamellar thickness with its direction... 

Fig. 10.16 Surface morphology of a lamellar single crystal of 512-mers grown from semi-dilute solutions in the dynamic Monte Carlo simulations. The view angle favors the exposure of the preferred orientations of fold ends in each sectors separated by the black thick lines (Hu et al. 2003b)...

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