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

该项目将探索二元聚合物共混物的热力学，同时表现出结晶和液-液相分离（LLPS）。本研究将使用无规聚苯乙烯-co-4-溴苯乙烯和氘化等规聚苯乙烯的模型共混体系。利用聚合物体系的优势，PI将通过系统地改变分子量、溴化水平、弹性和混合成分来调整相变（LLPS、结晶和玻璃化转变）。通过将主要的结构表征技术，包括散射（中子、x射线和激光）和成像工具（光学、电子和原子力显微镜）应用于具有良好相变的聚合物共混物，PI将(1)确定聚合物共混物的平衡相图，揭示LLPS和结晶的相互影响；(2)通过测量非平衡相图和一个相变在另一个相变的亚稳态中发生的动力学来了解热力学亚稳性；(3)测量LLPS和结晶同时发生的早期结构发展，了解单个转变的热力学驱动力和亚稳性调节的转变动力学之间的复杂平衡。这个项目的智力价值主要体现在三个方面。(1)塑料技术：该项目将使人们更好地理解聚合物共混物中共存的相变如何导致非平衡结构的发展，从而为工程塑料提供更好的材料和工艺设计。(2)相变基本原理：尽管人们对聚合物中单个相变的理解相对较好，但对聚合物中两个或多个共存相变之间相互作用的基本理解仍然相当有限。该计划将解决聚合物中共存转变的基本热力学的几个方面，弥合由相对较好研究的小分子和胶体系统跨越的相变的长度尺度谱的知识差距。(3)其他前沿：作为自组装手段的共存转换和竞争力对软物质的等级排序具有深远的影响，例如蛋白质聚集和错误折叠，这是生物医学研究的主要课题之一。对模型聚合物的透彻理解是揭示生物和其他软材料系统复杂性的重要一步。这个项目的广泛影响是高度整合的创新研究和动态教育计划的自然结果。涉及大学/工业/国家实验室合作的研究知识将通过出版物和演讲传播，并在新技术中实施。为了在聚合物材料和工程方面建立有效的教育计划，PI将开发本科和研究生课程，强调聚合物的加工-结构-性能-性能关系。鉴于汽车对塑料的需求日益增长，PI将与密歇根州的塑料和汽车公司建立强有力的联盟，通过合作研究和面向对象的教育来应对这一挑战。针对聚合物在汽车应用中的实际问题的高级设计项目将与包括伟世通和陶氏在内的工业合作伙伴共同开发。对K-12教育的拓展包括：(1)通过定期的材料和纳米技术主题讲座，参与当地学区的教育计划，并让高中生和教师参与该项目的研究。(2)为密歇根理工大学的青年项目在聚合物领域提供关键的新领导，其中包括鼓励女性和弱势群体从事工程和技术职业的特别项目。＊＊＊

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. ***