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The Effect of Thermal Treatment and Flow Processing on Melt-crystallization of P3HT and Propylene-ethylene Copolymers
The properties of semicrystalline polymers, such as conductivity, permeability, stiffness, and elastic modulus, are strongly dictated by their crystallization. It is well established that molecular attributes and processing parameters such as flow and thermal treatments can significantly affect crystallization kinetics and final morphological structures such as size, shape, and preferential orientation of crystals. Recent advances in synthesis and processing methods have afforded a great diversity of morphologies for semicrystalline polymers. However, several aspects of the impact of molecular characteristics, processing conditions, and presence of memory effects on crystallization remain elusive. Additionally, solventless processing of semiconductor polymers has received little attention in comparison to solution processing. Therefore, crystallization from the melt state in semiconductor polymers remains poorly understood. This dissertation addresses some of the questions in melt-crystallization for two different classes of polymers. On one hand, the role of shearing temperature and annealing time in flow-induced crystallization of two insulating copolymers is investigated, providing insight on how the final structure and properties may be tailored by appropriate choice of thermal parameters during and after imposition of flow. On the other hand, the nucleation and melt-crystallization of a semiconductor polymer (P3HT) is examined, in particular its self-nucleation behavior and the role of melt memory on crystallization. The obtained knowledge offers insight for development and refinement of processing methods to optimize the crystallization process and properties of state-of-the-art electronic devices. It has been observed that self-nucleation can be effectively used to alter the crystallization kinetics of P3HT. Additionally, the existence of a strong memory effect in as-synthesized P3HT has been discovered, which also significantly impacts the crystallization of this benchmark semiconductor polymer. The in-situ and ex-situ analysis of flow-induced morphologies for insulating propylene-ethylene random copolymers illustrate that flow-induced precursors can persist for long times even at temperatures above the nominal melting point, and thus affect the final morphology even for extended annealing times. It was also found that thread-like precursors can progressively decay during annealing up to point-like precursors, yielding a series of progressive structural evolutions.
Materials science|Polymer chemistry
Hosseinabad, Ramin, "The Effect of Thermal Treatment and Flow Processing on Melt-crystallization of P3HT and Propylene-ethylene Copolymers" (2019). ETD collection for University of Nebraska - Lincoln. AAI22616428.