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

本项目将探索同时表现出结晶和液-液相分离(LLP)的二元聚合物共混物的热力学。本研究将采用无规聚(苯乙烯-co-4-溴代苯乙烯)与氚代等规聚苯乙烯的模型共混体系进行研究。利用聚合物体系，PI将通过系统地改变相对分子质量、溴化程度、规整度和共混组成来调节相变(LLP、结晶和玻璃化转变)。通过主要应用结构表征技术，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)，PI将(1)确定聚合物共混物的平衡相图，并揭示LLP和结晶的相互影响，(2)通过测量非平衡相图和一个相变发生在另一个相变的亚稳状态下的动力学来了解热力学亚稳，以及(3)测量LLP和结晶同时发生的早期阶段结构发展，并了解单个相变的热力学驱动力和亚稳介导的相变动力学之间的复杂平衡。该项目的学术价值主要体现在三个方面。(1)塑料技术：该项目将使我们更好地了解由于聚合物共混物中共存的相变而导致的非平衡结构是如何发展的，这可能会导致更好的工程塑料材料和工艺设计。(2)相变基本原理：虽然对聚合物中单个相变的了解相对较好，但对聚合物中两个或更多共存相变之间的相互作用的基本理解仍然相当有限。该计划将涉及聚合物共存转变的基本热力学的几个方面，弥合相对研究较好的小分子和胶体体系跨越的相变长度-尺度谱方面的知识差距。(3)其他前沿：共存跃迁和竞争作用力作为一种自组装手段，对软物质中的层次排序具有深远的影响，例如在蛋白质聚集和错误折叠方面，这是生物医学研究的主要主题之一。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。%该项目的广泛影响是高度集成的创新研究和动态教育计划的自然结果。涉及大学/行业/国家-实验室合作的研究知识将通过出版物和演示文稿传播，并以新技术加以实施。为了建立有效的聚合物材料和工程教育计划，PI将开设本科和研究生课程，强调聚合物中的聚合-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大的联盟，通过合作研究和面向对象的教育来应对这一挑战。针对汽车中聚合物应用的实际问题的高级设计项目将与包括威斯蒂安公司和陶氏公司在内的工业合作伙伴一起开发。对K-12教育的推广包括：(1)通过定期讲授材料和纳米技术主题，与当地学区一起参与教育项目，并让高中生和教师参与该项目的研究。(2)在聚合物领域为密歇根理工大学的青年计划提供关键的新领导，其中包括鼓励女性和代表性不足的人群从事工程和技术职业的特别计划。***

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. ***