Collaborative Research: Dynamics of Ionomer Melts

1066517魏斯离聚体是具有强分子间吸引力的链状分子，由于链上的离子偶极子的强物理关联，使其表现出复杂的流动现象。相互作用的强度和结合的松弛时间取决于固定离子和移动反离子的性质、这些电荷的浓度以及流体变形的时间、温度和幅度。物理分子间缔合和离聚体熔体流动之间关系的细节尚不清楚，这在许多情况下阻碍了它们的商业应用。以往对离聚物流变学的研究由于无法将其与偶极相互作用和链缠结分离开来而受到阻碍。本研究的重点是表征一个模型离聚体系统的流变行为，轻磺化聚苯乙烯离聚体，其分子量低于发生链纠缠的地方。非磺化聚苯乙烯为劳斯链，只有偶极相互作用才会影响离聚体熔体的流变性能。该研究的具体目标是：1)了解移动反离子的性质如何影响流变性，特别是链的弛豫时间和离子结合；2)确定弹性如何在这些未纠缠的体系中发展，3)解决在离聚体熔体中观察到的剪切增厚的起源，以及4)了解如何使用低分子量添加剂来设计熔体流变学。该项目将包括离子单体的合成和表征，离子单体熔体的稳态、动态剪切和弛豫测量，以及熔体剪切变形过程中电离单体链结构的实时、小角中子散射评估。研究生将接受复杂流体和聚合物流变学领域的培训，这是美国聚合物行业日益需要的技能。高中生、本科生和研究生将参与研究。该项目是阿克伦大学和俄亥俄州阿克伦市一所当地高中之间的示范项目的一部分，该项目为10-12年级的学生提供了在该项目实验室进行探究式研究的机会。研究生和本科生将从学术项目中招收，并有针对性地从代表性不足的群体中招收学生。PI和从事这项研究的学生还将与阿克伦全球聚合物学院合作，开发复杂流体的教学和示范辅助工具。离聚体用于各种商业应用，包括商品热塑性塑料，热塑性弹性体，膜（例如，用于燃料电池，反渗透，加湿和电池），聚合物混合物的增容剂，粘合剂，碳氢化合物溶液增粘剂，钻井泥浆和有机凝胶。了解离聚体的流变行为，以及如何通过组成、外部变量（如温度和应力）和添加剂来控制流变性，对于这些应用以及从这些聚合物中加工薄膜和成型制品都是重要的。详细了解如何设计离子聚合物熔体的加工行为，同时仍能实现这些材料的理想物理和机械性能，这可能会带来新技术，例如功能薄膜的挤压和卷对卷加工，这些技术目前由溶液铸造和批量工艺主导。

1066517Weiss Ionomers are chain molecules with strong attractive intermolecular forces that exhibit complex flow phenomena due to strong physical associations of the ionic dipoles attached to the chains. The strength of the interactions and the relaxation times of the associations are dependent on the nature of the fixed ion and the mobile counterion, the concentration of such charges and the time, temperature and amplitude of the deformation of the fluid. The details of the relationship between the physical intermolecular associations and the melt flow of ionomers is poorly understood, and this has hampered, in many cases, their commercial application. Previous research on the rheology of ionomers has been hindered by the inability to separate effects from the dipolar interactions and chain entanglements. This research focuses on characterizing the rheological behavior of a model ionomer system, lightly sulfonated polystyrene ionomers, with molecular weight below that where chain entanglements occur. The unsulfonated polystyrene is a Rouse chain, and only the influence of the dipolar interactions will affect the rheological properties of the ionomer melts. The specific objectives of the research are: 1) to develop an understanding of how the nature of the mobile counterion affects the rheology, specifically the relaxation times of the chain and the ionic associations; 2) to determine how elasticity is developed in these unentangled systems, 3) to resolve the origin of shear-thickening that has been observed in ionomer melts, and 4) to understand how low molecular weight additives can be used to engineer the melt rheology. The project will include the synthesis and characterization of the ionomers, steady state, dynamic shear and relaxation measurements of tionomer melts, and real-time, small angle neutron scattering evaluation of the ionomer chain structure in the melt during shear deformation. Graduate students will be trained in the field of complex fluids and polymer rheology, skills that are increasingly in demand by the U.S. polymer industry. High school, undergraduate and graduate students will participate in the research. The PI is part of a demonstration program between the University of Akron and a local high school in the city of Akron, OH, that provides opportunities for students, grades 10-12 to carry out inquiry-based research in the PI's laboratory. Graduate and undergraduate students will be recruited from academic programs and by targeted recruiting of students from underrepresented groups. The PI and students working on this research will also cooperate with the Akron Global Polymer Academy to develop teaching and demonstration aids on complex fluids. Ionomers are used in a variety of commercial applications, including commodity thermoplastics, thermoplastic elastomers, membranes (e.g., for fuel cells, reverse osmosis, humidification and batteries), compatibilizers for polymer blends, adhesives, hydrocarbon solution viscosifiers, drilling muds and organogels. An understanding of the rheological behavior of ionomers and how to control the rheology by composition, external variables such as temperature and stress, and with additives is important with regard to those applications, as well as for processing films and shaped articles from these polymers. A detailed understanding of how to engineer the processing behavior of ionomer melts while still achieving the desirable physical and mechanical properties of these materials could result in new technologies, such as the extrusion of functional thin films and roll-to-roll processing, technologies that are currently dominated by solution casting and batch processes.