Segmental rotation

When anisotropy increases with the increase of molecular mass of rotating unit. For instance, the sensor segment rotates rapidly and massive target binding decreases this rate. The target binding can also displace small competitor to solution with increase of its rotation rate. 

A crucial aspect of our approach is based on the idea that segmental rotation is activated thermally as the simplest mode of collective motions. This kind of first order distortion substantiated by oscillatory or diffusive segmental rotation is possible in a crystal lattice as well. This must not necessarily affect the ideal periodic structure but can be discussed in terms of the molecular structure factor. 

Collective segmental rotation is considered to be the natural form gaining conformational entropy as the essential factor for stabilizing mesophases or liquid-crystalline structures. Despite the approximate character of our conception it should be possible to identify the significant characteristics of the intermolecular segmental arrangement in mesophases, in liquid crystals or in a polymer melt. 

The molecular mechanism of local segment rotations can be explained by the occurrence of twin reversals [33, 34] which are induced thermally due to the unusual course of the conformational potential [35]. Those twin reversals are torsion defects causing the helix conformation to change from left-handed to right-handed and vice versa. They are built into the PTFE helix without changing the direction of the molecular long axis (Fig. 23). Additionally, the long... 

Fig, 3, Segment rotation leading to a chain molecule from Position II to III... 

It is now generally accepted that the viscous flow of polymeric liquids is connected with chain segment rotation, i.e. with configurational entropy. From this point of view Miller concluded that the Simha-Boyer equation was not correct since the relative free-volume in SB theory equals zero at 0 K, not at T = T0. If the latter... 

Thus, in dependence on the way of macromolecule conformation change, ratio of life times of salt bonds and correlation time of macromolecule segment rotation, change of local macromolecule units density, under formation of complex polyelectrolyte-SAS segment mobility of macromolecule may be increased, decreased or remains constant. 

A) The presence of a methyl group in the a-position results in a hinderance to the segmental rotation of the polymer backbone. As a result, polymethacrylates are invariably harder, less extensive polymers than the corresponding acrylates (7) (Table I). 

B) Similarly, as the length of the ester side chain increases, segmental rotations in the side chain, as well as an increase in the specific volume of the polymers, result in freer segmental motion within the polymer chain, with a concomitant decrease in tensile strength and an increase in the extensibility of the polymers (Table I). When one considers that commercial acrylic polymers are almost... 

The viscosity which yields the maximum reaction rate, shifts to a lower value with increasing temperature in GTA. In KF-54, however, the maximum viscosity stays almost constant. This behavior suggests the existence of a factor which affects the reaction rate but does not contribute to the macroscopic viscosity. If this second contribution to the microscopic friction decreases with increasing temperature, the behavior shown in Fig. 3.28 is to be expected. This second factor may be related to local segmental rotation of the siloxane chain. However, further experiments are necessary for detailed analysis. 

Steric effects of the silicon s organic substituents are not limited to the simple diluent effect. If the organic substituents of neighboring Si atoms are sufficiently bulky, they can restrict the freedom of segmental rotation about the Si—O bonds of the chain. To the... 

Figure 2. Types of motion in polymer molecules (a) translational (b) segmental rotation (c) group rotation. Reprinted, with permission, from J. E. Guillet, Polymer Physics and Photochemistry, Cambridge University Press, Cambridge, England, 1985, p. 2.

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