Relaxation phenomena, polymer crystals

The self-organizing nature of liquid crystal polymers is reflected in their complex flow behavior. The relaxation phenomenon of lyotropic polymer solution after shear cessation leads to band texture morphology that can be further induced to isotropic materials. Future research should focus on solvents influence on band size implicitly related to the induced pattern in polymers with different structures. Another aspect that could be explored is the imidization of patterned polyimide precursors and those conditions in which the texture is still maintained. 

As is well-known, the rate of nucleation is enhanced by the application of a deformation to the polymer melt (2/i). But only recently, a theory of shear induced crystallization could be developed (25). This type of crystallization causes highly oriented boundary layers in injection molded articles (cf.ref. 8). Shear induction is an elastico-viscous relaxation phenomenon. So far, however, this perception did not contribute to a simplification of the situation. 

At the same time the phenomenon of fracture reflects, in one way or another, the ultimate limit of deformation in a solid. It thus involves fundamental physical properties of the material such as its inter-atomic bonding, its surface energy and its crystal structure. It also involves crystallographic processes such as slip, stress induced phase transformations and twinning, whilst in molecular solids such as polymers other processes such as molecular relaxation behaviour may predominate. Fracture is clearly of great scientific interest and has attracted the attention of chemists and solid state physicists as well as engineers. 

Data reported on the low-temperature crystallization (at —90 C) of (PDMS), by. Y-ray and proton n.m.r., show that crystallization is a bulk phenomenon and not surface induced. Dielectric studies on amorphous and crystalline polymers have been reported. Dynamic Kerr-effects and dielectric relaxation studies of a poly(methylphenyl siloxane) have been reported in the region of its relaxation progress, and it is suggested that a substantial contribution to the process is due to motions about the silicon-aromatic ring bond. ... 

Most thermoplastic polymers have a strong tendency to crystallize during cooling. This phenomenon generally results in an isotropic arrangement of the macromolecules and must be controlled to ensure orientation in the fibre direction. The relaxation of the macromolecular chains at the exit of the dies causes a die swell phenomenon, which must also be treated to optimize the final properties of the yarns. 

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