Dynamics of Polymer Mixtures: Intermolecular Coupling and Crystallizability

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TECHNICAL SUMMARY:Previous research on segmental and local dynamics of associating polymer blends and solutions, carried out with NSF-DMR support, focused on the roles of composition, intermolecular hydrogen bonding strength, and intrinsic component mobility differences. This research was conducted principally using dielectric spectroscopy, taking advantage of its ultra-broad frequency range and high sensitivity. This earlier work prompted a number of fundamental questions that will be answered through the proposed research. For example, what is the role of strong intermolecular coupling on the segmental dynamics when self-association of the component polymers is minimized? At what length scale does the segmental dynamics crossover from homogeneous to heterogeneous character? The second part of the proposed work seeks to establish the origin of a novel fast process observed in the dielectric spectra of miscible blends. The principle questions to be addressed in this part of the research include: Does component polymer crystallizability play an important role in determining heterogeneity of miscible blends between weakly associating polymers? Are such blends capable of capturing nascent crystal formation and hence serving as model systems for the investigation of crystal nucleation, the most significant unresolved problem in the field of polymer crystallization?NON-TECHNICAL SUMMARY:Mixing of unlike polymers is known to be an efficient and cost effective means of creating novel alloys with enhanced properties, and has important industrial and fundamental significance. Mixing is facilitated by the formation of strong intermolecular bonding between the two polymers, but little is known about the precise role such strong bonding plays in modifying molecular, and consequently macroscopic, properties. The first part of the proposed research focuses on the investigation of intermolecular bonding strength on the mobility of the component polymers in the mixture. The second portion seeks to understand the influence of component polymer ordering (crystallization) on mixture mobility. The latter systems will also serve as models for the investigation of crystal nucleation, the most significant unresolved problem in the field of polymer crystallization.This program broadly impacts the field of materials research in several ways. The proposed research will create learning opportunities for graduate and undergraduate students, including building teamwork skills from frequent group and inter-group meetings where ideas are exchanged. Each participant in the program will be engaged in the extensive and vital outreach program of the Penn State Center for Nanoscale Science, an NSF Materials Research Science and Engineering Center. Finally, collaborative studies will be undertaken with the research group of Prof. George Floudas (U. Ioannina, Greece), and an exchange of student researchers with his group is anticipated over the course of this program.