Dependence of mechanical properties of partially oriented polymeric systems on chemical structure and molecular architecture
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Partially oriented polymeric structures such as semi-crystalline polymers and liquid crystalline polymers/elastomer cover a wide range of synthetic and natural polymeric materials. Owing to the significant differences between the molecular structure and properties of ordered and amorphous regions, semi-crystalline polymers show complex patterns of behavior, although the molecular level mechanisms for deformation are still not well-understood. Molecular dynamics simulation based on a united atom method were performed, to study the crystallization behavior and molecular response of semi-crystalline polyethylene structures under external stresses in a time scale of nanoseconds to capture the molecular details. Using the data from molecular dynamics simulations, the effect of lamellae orientation on the stress-strain behavior was evaluated to understand the morphological evolution during deformation. The stress-induced morphological changes of free-standing and supported thin films with strong interacting surfaces were also investigated. Process-structure-property relationships are also investigated for liquid crystalline elastomers, with experimental approaches for validation. Structures and properties of a series of azobenzene containing liquid crystalline elastomeric films were characterized in detail.