Degree chain orientation

Figure 11 shows that the molecular weight distribution in the melt (presence of short chains) can account for the coexistence of two types of crystals in the absence of molecular orientation or at a slight stretching of the melt. However, there is a purely thermodynamic reason for the appearance of this main structural feature of samples crystallized under conditions of molecular orientation, even at high degrees of orientation, when virtually the whole distribution function is displaced into the region of /S > /3cr. 

For fibres made from the same polymer but with different degrees of chain orientation the end points of the tensile curves, a5, are approximately located on a hyperbola. Typical examples of this fracture envelope are shown in Figs. 8... 

By neglecting the chain extension it is assumed that Wb=Wbs. Thus the observation that Wb is approximately constant for fibres of the same polymer with different degrees of orientation means that not only a constant critical shear stress, rb, but also a maximum shear strain, (0-0b), is a useful criterion of... 

The observed range of the shear modulus varies between 1.5 GPa in filaments of regular count to 3 GPa in microfilaments, which correlates with the degree of orientation and crystalline perfection in the fibres [40]. Compared to the theoretical value of the modulus of shear between two hydrogen-bonded chains of 4.1 GPa, it indicates softening due to the van der Waals bonding between the hydrogen-bonded planes. 

The proposed relation between the strength and the modulus of the fibre and the relation between the degree of chain orientation and the concentration of the spinning solution yield a relation between strength and concentration... 

The development of -conjugation system and high degree of orientation in the PAV LB films arise from the orientational orderliness of the precursor chains in the LB films. The precursor polymers should form two-dimensional orientation... 

The motional characteristics of interest are typically those governed by the phospholipid fatty acyl chains and head-group region and the neutral lipid or protein components of membranes. Rotational motion can be subdivided into a structural component, the order or degree of orientational constraint,... 

The observation that r(t) decays to the finite value rro soon led to the recognition that the fluorophore DPH has an orientational motion which is restricted due to the surrounding lipid chains/35-37 From this the wobbling-in-cone model(37 43 44) was developed. In this model, DPH was assumed to wobble within a cone of half angle 6C (which relates to the degree of orientational constraint, order, or rm) with a wobbling diffusion constant D (which relates to the rate of motion) with... 

A number of other characteristics are required in order to ensure a viable polymeric conductor. Chain orientation is needed to enhance the conducting properties of a polymeric material, especially the intermolecular conduction (i.e., conduction of current from one polymer molecule to another). This is a problem with many of the polymers that are amorphous and show poor orientation. For moderately crystalline or oriented polymers, there is the possibility of achieving the required orientation by mechanical stretching. Liquid crystal polymers would be especially advantageous for electrical conduction because of the high degree of chain orientation that can be achieved. A problem encountered with some doped polymers is a lack of stability. These materials are either oxidants or reductants relative to other compounds, especially water and oxygen. 

IR spectroscopy is not only useful for determining the chemical constitution of polymers. It additionally provides profound information on chain orientation and on the orientation of attached lateral substituents of polymers. In this case, polarized IR radiation is applied which is only absorbed by an IR-active bond if the plane in which the electrical field vector E of the IR beam oscillates is parallel to the transition dipole moment p of the vibration to be excited. If, on the other hand, the transition dipole moment p is perpendicular to the electrical field vector E of the IR beam no absorption is observed. Using this effect, the degree of orientation of a polymer sample (film, fiber) can be estimated by comparing the intensity at maximum /(11) and at minimum I ) absorption, i.e., the dichroic ratio. 

From half width of the intensity distribution measured along the Debye ring of reflection derived from a distance between polymer chains obtained by X-ray diffraction, the practical standard value of parallelism degree in orientation was determined to be 0.92. 

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