Orientation of segments

The development of the internal orientation in formation in the fiber of a specific directional system, arranged relative to the fiber axis, of structural elements takes place as a result of fiber stretching in the production process. The orientation system of structural elements being formed is characterized by a rotational symmetry of the spatial location of structural elements in relation to the fiber axis. Depending on the type of structural elements being taken into account, we can speak of crystalline, amorphous, or overall orientation. The first case has to do with the orientation of crystallites, the second—with the orientation of segments of molecules occurring in the noncrystalline material, and the third—with all kinds of structural constitutive elements. 

A protein s primary structure is its amino acid sequence. Its secondary structure is the orientation of segments of the protein chain into a regular pattern, such as an a-helix or a P-pleated sheet. Its tertiary structure is the three-dimensional shape into which the entire protein molecule is coiled. 

Abstract The discussion of relaxation and diffusion of macromolecules in very concentrated solutions and melts of polymers showed that the basic equations of macromolecular dynamics reflect the linear behaviour of a macromolecule among the other macromolecules, so that one can proceed further. Considering the non-linear effects of viscoelasticity, one have to take into account the local anisotropy of mobility of every particle of the chains, introduced in the basic dynamic equations of a macromolecule in Chapter 3, and induced anisotropy of the surrounding, which will be introduced in this chapter. In the spirit of mesoscopic theory we assume that the anisotropy is connected with the averaged orientation of segments of macromolecules, so that the equation of dynamics of the macromolecule retains its form. Eventually, the non-linear relaxation equations for two sets of internal variables are formulated. The first set of variables describes the form of the macromolecular coil - the conformational variables, the second one describes the internal stresses connected mainly with the orientation of segments. 

The relaxation of orientation of segments is intrisinsigly included in the theory from the very beginning. Indeed, in Chapter 3, discussing the main assumption of the theory, we assumed that there is an underlying relaxation process, which is described by relaxation equation (3.14), that is... 

One can guess that this relaxation process describe the relaxation of mean orientation of segments with the relaxation time r. It is remarkable that for... 

In the steady state, one can find the mean orientation of segments from equation (7.49)... 

One can see that the velocity gradients directly affect the mean orientation of segments, while the effect of the disturbed conformation of macromolecules (the end-to-end distance) can be neglected here in comparison with the latter. 

One can apply formula (7.44) to every subchain of the macromolecule, assuming that every subchain of the macromolecule is in the situation of equilibrium. Perhaps, it is possible to reach such a division of a macromolecule in subchains that the distribution of orientation of segment is the equilibrium one, though the entangled system is in deformed state, but the problem about distribution of orientation of the interacting, connected in chains, segments apparently is not solved yet. 

Abstract Macromolecular coils are deformed in flow, while optically anisotropic parts (and segments) of the macromolecules are oriented by flow, so that polymers and their solutions become optically anisotropic. This is true for a macromolecule whether it is in a viscous liquid or is surrounded by other chains. The optical anisotropy of a system appears to be directly connected with the mean orientation of segments and, thus, it provides the most direct observation of the relaxation of the segments, both in dilute and in concentrated solutions of polymers. The results of the theory for dilute solutions provide an instrument for the investigation of the structure and properties of a macromolecule. In application to very concentrated solutions, the optical anisotropy provides the important means for the investigation of slow relaxation processes. The evidence can be decisive for understanding the mechanism of the relaxation. 

In the equilibrium situation, at a given end-to-end distance R of a macromolecule, the tensor of mean orientation of segments of a chain is determined (Flory 1969) as... 

One admits that the relative permittivity tensor of the system is determined by the mean orientation of the segments, so that we consider expression (10.13) to be equivalent to the first-order terms of relation (10.6) and, at comparison, obtain the expression for the mean orientation of segments of macromolecules in an entangled system... 

One can see that, in this approximation, disturbed conformation of macromolecules does not affect the mean orientation of segments in the steady state, that can be found from equation (10.15) as... 

In contrast to the case of dilute polymer solutions (relation (10.7)), mean orientation of segments does not depend (to the first approximation) on the large-scale conformation of the macromolecule. However, an independent calculation of the tensor of orientation in non-equilibrium situations is much desirable. 

Using extension and compression tests to develop the relationship between stress and strain and then to conclude that orientation of segments of kamaboko s network was negligible, and similar to the behavior of the vulcanized rubber in small deformation. 

Fig. 23. A Kuhnian chain (schematic representation). The Sj are courses along the chain. The Uj are vectors defining the size and the orientation of segments.

However, it has to be noted that the physical meaning of the corrosion potential in this case carmot be interpreted by conventional electrochemical kinetics. As long as no currents are present, the information gained on the irmer interface potential could be determined by dipole orientation of segments of the polymer chain. 

Sketch of the molecular orientation, of segments of a polymer molecule between entanglements, that develop in melt flow. 

In other words, at the ejqtense of shear deformation appears reducing to electromagnetic anisotropy of enviromnent orientation of segments in every point of polymer dielectric, in this time is being it is polarization. 

Stress-optical Orientation of segments Orientation limited to (a)... 

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