The proposed research aims to investigate several newly discovered phenomena of orientation-induced crystallization precursor structures in multi-component polymer melts under flow. The phenomena include (1) formation of precursor structures at both nanoscopic and macroscopic scales, which can act as multi-scaled scaffolds to guide the crystallization process, and (2) the relationships among the flow-induced precursor structures, rheological behavior, multi-component phase behavior and type of flow field. To tackle the proposed problems, following research plans have been composed. First, the chosen multi-component systems, all based on polyolefin will include polymer blends of model compounds (e.g. high molecular weight crystallizable species and low molecular weight non-crystallization species), segmental olefin block copolymers (with only one crystallizable block) and polyolefin nanocomposites with well dispersed surface-modified carbon nanofibers/nanotubes. Second, to understand the rheological behavior, experimental data in dynamic and transient modes will be described by a GEX-based model in order to yield relaxation mechanisms responsible for the formation of precursor structure. Third, the development of structure in real time will be following by the use of combined methods including rheology, in-situ synchrotron small-angle-X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD) and light scattering techniques. Finally, to understand the effect of different flow fields, results from simple shear (containing the rotational element) and extensional flow (without the rotational element) will be compared. NON-TECHNICAL SUMMARY: The subject of flow-induced crystallization, especially in multi-component systems such as polymer blends, block copolymers and nanocomposites, remains to be one of the most important problems in polymer science and engineering today. With the availability of synchrotron X-ray scattering and diffraction methods, and the coupling of rheology and light scattering techniques, many unanswered questions of fundamental importance can now be suitably addressed. It is known that molecular orientation induced by flow during polymer processing operations can deeply affect the crystallization kinetics as well as the final polymer morphology and properties. The knowledge obtained in the proposed study will significantly enhance our ability to understand the relationships between structure, phase behavior, process and property in multi-component systems containing crystalline components. The information will lead to developments of improved polymer processes and new polymer products, thus benefiting the polymer industry in specific and the society in general. The broader impacts of this proposal are several. The immediate benefit is that the proposed activities will produce tight links between academic and government institutions (i.e., Stony Brook University, National Synchrotron Light Source). Students and scientists will be trained in both institutions and receive interdisciplinary research experiences. They will be exposed to relevant industrial problems and will have a chance to tackle these problems with direct interactions from industrial scientists. They will also be involved in the Stony Brook and Brookhaven National Laboratory summer research programs, where they will supervise high school and undergraduate students as well as industrial scientists to carry out synchrotron X-ray experiments and related in-laboratory studies.
