Critical regimes of deformation of liquid polymeric systems
The principal peculiarity of typical polymers at temperatures above the glass-transition region and the melting point is their ability to exist in two physical states — fluid and high-elastic (rubbery). Accordingly, they manifest two main relaxation mechanisms. In the fluid state, irreversible displacement of the centres of gravity of macromolecules relative to each other is possible, and irreversible deformations may be infinitely large. In the high-elastic (rubbery) state, the determining role is played by rapid changes in the spatial arrangement of groups of atoms forming the macromolecular chain, and this enables it to unwind, thereby accumulating a considerable amount of reversible (high-elastic) deformation. In the fluid state polymers manifest both relaxation mechanisms, and during the flow they may accumulate large amounts of reversible deformations.
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