Polymer orientation mechanism

The orientational mechanism of EB in solutions of r id-chain polymers and the possibility of determining rotatory diffusion constants of their molecules from dispersion curves may be utilized for the characterization of equilibrium conformational properties of their drains. The theory of rotational friction of kinetically rigid molecules developed by Hearst makii% use of the statistics of worm-like chains can be employed for this purposes. The results of this theory for the two limiting cases of molecular conformation refering to the slightly bent rod and the worm-like coil are expressed by Eqs. (27) and (28) (Sect. 2.3). 

However, this mechanism of motion does not provide any great contribution to the Kerr effect since the dispersion curves of EB fall to virtually zero (Fig. 60). This difference may be interpreted by the proportionality of the orientational EB of a ripd-chain polymer to the square of the number of monomer units in segment whereas increment Ae/c related to the orientational mechanism is proportional to S (see Sects. 5.8 and 5.9). Hence, in the case of dielectric polarization the part played by the deformational mechanism as cmnpared to the orientational mechanian can be more important than in the case of EB. 

The deformation of long chain polymer molecules has always been of great industrial interest as more value can be placed on a material that has improved properties. Molecular extension, or alternatively molecular orientation, is of particular interest as it can enhance mechanical properties of an otherwise weak polymer. Oriented materials are inherently anisotropic. These anisotropic regions can be found directly in semicrystalline polymers where chains organize themselves into crystalline domains. 

In accordance with the discussion of Figures 9.25c and d, they reflect a sUghtly positive orientation for PHB and PLA in the matrix and an opposite orientation for the two polymer components (PHB negative, PLA positive) in the islands . These figures clearly demonstrate that the polarization spectra recorded with a single-element detector cannot discriminate between the different orientation mechanisms in the phase-separated, anisotropic structure of this polymer blend. 

HCl-doped to the emeraldine salt. Similar increases in elastic modulus would be expected to result from the mechanical drawing, because the process causes considerable alignment of the polymer chains in the draw direction. In one study, drawn EB films gave a room temperature modulus of 12 GPa,84 which is considerably higher than is typical of unoriented polymers. Such mechanical orientation also increases the crystallinity84 and conductivity of the PAn films and fibers. 

The most efficient orientation fields are exten-sional. Using convergent and divergent flow one may control orientation of anisometric particles. Most of the work in this area has been done with fiber-filled materials but the effects are equally important for flow of neat semicrystafline polymer melts or liquid crystal polymers [Goettler and Shen, 1983 Goettler, 1984]. There is less information on the flow-induced orientation of platelets. In extensional flow, these particles are less susceptible to orientation. Two-stage orientation mechanism was observed in converging flow [Utracki, 1988]. 

In addition to the polar order produced by the electric field, Ep, axial order may be present due to either intrinsic ordering (e.g., in liquid-crystalline polymers) or mechanically induced ordering (e.g., uniaxial elongation). For rod-like molecules with dominant dipole and hyperpolarizability directed along the molecular axis, i.e. /u and only, in uniaxial systems, the orientational distribution function G (0) can be expanded in terms of Legendre polynomials... 

In describing flowing polymeric liquids it is probably not feasible to use detailed models that describe the locations of all the atoms in the polymer molecules. Consequently, it is necessary to use some kind of mechanical models that portray the overall molecular architecture. Bead-spring models have been widely used with considerable success for relating macroscopic properties to the main features of the molecular architecture. Even the simplest of these models - the elastic dumbbell models - are capable of describing polymer orientation and polymer stretching. More complicated chain, nng, and star models reflect better the molecular structure and allow for the portrayal of the most important internal molecular motions as well. 

Phase-locked electronics are used to record the dynamic IR spectral change in-phase and out of phase with the applied mechanical field. The method provides insight to the response to the external stress on the molecular and submolecular scale. Rheooptical FTIR spectroscopy is one of the few techniques providing data on the crystallisation, orientation and conformational changes of a polymer during mechanical treatment (83). Two dimensional correlation analysis is utilised to enhance the information derived from the vibrational spectroscopic data. 

Oriented PET in the glassy states is a useful system when investigating the effect of orientational order on polymer crystallization mechanism. The crystallization rate of PET is slow enough for time-resolved measurements to... 

For the practical analysis of orientation phenomena in polymers mathematical relations between the parameters of distribution function models of the chain axes and the dichroic ratio have been derived and can be evaluated in terms of the experimentally measured values. Although this approach is restricted to relatively simple models, it has been extensively applied to establish the basic concepts of orientation mechanisms in a great variety of polymeric systems. In what follows the results of such calculations for some selected distribution models will 1% discussed. 

The above is certainly the case in experiments where an extruder is placed on a beamline in order to survey the structural developments in the fiber as a function of the distance from the spinnerette. This specific subject is discussed in later sections. Complicated experiments on contracting muscles, gels containing viruses, oriented polymer nanocomposites, mechanically induced ordering in samples subjected to stress, etc, also fall imder the remit of fiber diffraction. 

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