CAREER: Equilibrium Thermodynamics and Thermodynamic Metastability in Polymer Blends with Coexisting Liquid-Liquid Phase Separation and Crystallization

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This project will explore the thermodynamics of binary polymer blends that exhibit both crystallization and liquid-liquid phase separation (LLPS). A model blend system of atactic poly(styrene-co-4-bromostyrene) and deuterated isotactic polystyrene will be used for this study. Taking advantage of the polymer system, the PI will tune the phase transitions (LLPS, crystallization, and glass transition) by systematically varying molecular weight, bromination level, tacticity and blend composition. By applying primarily structural characterization techniques including both scattering (neutron, X-ray and laser light) and imaging tools (optical, electron, and atomic force microscopy) to polymer blends with well-positioned phase transitions, the PI will (1) determine the equilibrium phase diagrams of polymer blends and reveal the mutual influence of LLPS and crystallization, (2) understand thermodynamic metastability by measuring non-equilibrium phase diagrams and the kinetics of one phase transition occurring in a metastable state of another transition, and (3) measure the early stage structure development during simultaneous LLPS and crystallization and understand the intricate balance between the thermodynamic driving forces for individual transitions and the metastability-mediated transition kinetics. The intellectual merits of this project manifest mainly in three areas. (1) Plastics Technology: This program will lead to a better understanding of how non-equilibrium structures develop due to coexisting phase transitions in polymer blends, which could results in better material and process designs for engineering plastics. (2) Phase Transition Fundamentals: Although individual phase transitions in polymers are relatively well understood, the fundamental understanding of the interplay between two or more coexisting transitions in polymers is still rather limited. This program will address several aspects of the fundamental thermodynamics of coexisting transitions in polymers, bridging the knowledge gap in the length-scale spectrum of phase transitions spanned by the relatively well-studied small molecular and colloidal systems. (3) Other Frontiers: Coexisting transitions and competing forces as a means of self-assembly have profound implications in hierarchical ordering in soft matter, such as in protein aggregation and misfolding, one of the major topics in biomedical research. A thorough understanding of model polymers is an important step toward revealing complexities in biological and other soft materials systems.%%%The broad impacts of this project are a natural outcome of highly integrated innovative research and dynamic education programs. The knowledge from the research involving university/industry/national-laboratory collaborations will be disseminated through publications and presentations, and implemented in novel technologies. To establish an effective education program in polymer materials and engineering, the PI will develop both undergraduate and graduate courses that emphasize rocessing-structure-property-performance relationships in polymers. In light of the increasing demands for plastics in automobiles, the PI will forge a strong coalition with Michigan's plastic and automotive companies to address the challenge through both collaborative research and object-oriented education. Senior Design projects targeting real problems in polymer applications in automobiles will be developed with industrial partners including Visteon and Dow. Outreach to K-12 education includes: (1) Participating in education programs with the local school district through regular lectures on topics of materials and nanotechnology and involving high school students and teachers in researches in this project. (2) Providing key new leadership in the area of polymers for Michigan Tech's Youth Programs, which include special programs for encouraging women and underrepresented populations to pursue engineering and technical careers. ***