Chain - direction

Di stefano D L and Wand A J 1987 Two-dimensional NMR study of human ubiquitin a main chain directed assignment and structure analysis Biochemistry 26 7272-81... 

The chain direction within the crystal is along the short dimension of the crystal, indicating that the molecule folds back and forth, fire hose fashion, with successive layers of folded molecules accounting for the lateral growth of the platelets. 

The PVC crystaUites are smaU, average 0.7 nm (3 monomer units), in the PVC chain direction, and are packed lateraUy to a somewhat greater extent (4.1 nm) (21,33). A model of the crystaUite is shown in Figure 6. The crystalline stmcture of PVC is found to be an orthorhombic system, made of syndiotactic stmctures, having two monomer units per unit cell and 1.44—1.53 specific gravity (34—37). 

Performance of an imaginary 1,2-shift on the benzhydrol antihistamines, that is, attachment of the side chain directly to the benzhydryl carbon while leaving the hydroxyl group intact, affords a series of molecules with markedly altered biologic activities. 

In the secondary nucleation stage, the remaining amorphous portions of the molecule begin to grow in the chain direction. This is schematically shown in Fig. 16. At first, nucleation with the nucleus thickness /i takes place in the chain direction and after completion of the lateral deposition, the next nucleation with the thickness k takes place, and this process is repeated over and over. The same surface nucleation rate equation as the primary stage can be used to describe these nucleation processes. 

Figure 11 Eiectrical resistivity of PET fiber versus average crystaliite size perpendicuiar to the chain direction.

Many of the dangerous reactions previously mentioned affect the carbon chain directly. However, they are listed in the previous paragraphs for classification... 

Phospholipids are amphiphilic substances i.e. their molecules contain both hydrophilic and hydrophobic groups. Above a certain concentration level, amphiphilic substances with one ionized or polar and one strongly hydrophobic group (e.g. the dodecylsulphate or cetyltrimethylammonium ions) form micelles in solution these are, as a rule, spherical structures with hydrophilic groups on the surface and the inside filled with the hydrophobic parts of the molecules (usually long alkyl chains directed radially into the centre of the sphere). Amphiphilic substances with two hydrophobic groups have a tendency to form bilayer films under suitable conditions, with hydrophobic chains facing one another. Various methods of preparation of these bilayer lipid membranes (BLMs) are demonstrated in Fig. 6.10. 

First, we note that the cr-cr nature of the lowest excited state of long-chain polysilanes predicted by the semiempirical calculations described in detail below implies a transition moment direction lying approximately along the chain direction rather than perpendicular to it. Evidence for such an orientation of the transition moment has been obtained in measurements on solid polysilane samples (19,36). This... 

We now report that in the region of the absorption band the flow linear dichroism of a solution of 1 is positive (Fig. 3). Assuming that the nature of the flow orientation is of the usual kind, i.e., that the polymer chains in a random coil conformation which dominates in solution (34) tend to align with the flow direction, this observation provides additional support for the absolute assignment of the transition moment direction along the chain direction, even in solution. Similar conclusions based on polarization studies on a stretched film of poly(di-n-hexyl silane) have recently been reported (36). 

Polymers that are built from the repetition of identical "repeat units" are called "homopolymers" (from ancient Greek "d/iog — same).2 Linear homopolymer chains are obtained upon linking chemically identical units exclusively at both ends. However, repeat units are not always symmetrical in the chain direction. Depending on the orientation of the repeat unit, different microstructural... 

The low-frequency LAM in Raman spectroscopy is a vibrational mode pertaining to ordered sequences in the chain direction. The mode frequency (An) is inversely proportional to the ordered chain sequence length or to the crystallite thickness. This relation was given by Shimanouchi and co-workers [92,93] as ... 

Here m is the mode order (m — 1,3,5. .., usually 1 for polyethylenes), c the velocity of light, p the density of the vibrating sequence (density of pure crystal) and E the Young s modulus in the chain direction. The LAM band has been observed in many polymers and has been widely used in structural studies of polyethylenes [94—99,266], as well as other semi-crystalline polymers, such as poly (ethylene oxide) [267], poly(methylene oxide) [268,269] and isotactic poly(propylene) [270,271], The distribution of crystalline thickness can be obtained from the width of the LAM mode, corrected by temperature and frequency factors [272,273] as ... 

For USAXS and SAXS data the tangent-plane approximation is valid and the relation between scattering angle and the units of reciprocal space are given by Eq. (2.7). If the scattering pattern is properly aligned with the vertical direction identical to a fiber axis or the polymer chain direction, then sy = 53. In similar manner the. vx-axis of the detector is related to the actual orientation of the sample with respect to the beam. 

Fig. 9 Snapshot of a single crystal of lattice polymers viewed from the chain direction. The bonds are drawn as solid cylinders. The viewing angle is large for better observation of folds. The chain length is 512 units and the thickness of the crystallite is about 12 units. The dissolved chains are not shown for clarity [57]...

Fig. 18 Schematic picture of the system for simulating polymer crystallization from the dense melt. Polymer chains that should be crystallized are sandwiched between parallel side surfaces of the lamellae made of the same polymer chains. The z-axis is taken normal to the substrate, while the y-axis is along the chain direction of the substrate crystals...

The crystalline lamellar thickness Dc obtained by StrobPs method is initially 1.4 nm and grows to about 2.0 nm, which is roughly equal to the crystallite size in the chain direction of 2.8 nm estimated from the wide-angle X-ray diffraction (WAXD) [7]. Interestingly, the persistence length /p = 1.45 nm just before crystallization measured by SANS (also see Fig. 11) [9,10] is almost equal to the crystal thickness. 

Fig. 14 The four normal stresses and the four shear stresses acting on a domain resulting from a tensile stress on the fibre. A crack is drawn parallel to the chain direction. The angle in the loaded state between the domain axis and the fibre axis is 6... 

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