Collaborative: Investigation of the Consequences of Cooperative Motion in Polymers and their Miscible Blends

协同运动被广泛认为是玻璃形成液体动力学的重要组成部分，但人们对协同运动的长度尺度却知之甚少。本文提出了实验和计算机模拟来解决聚合物中的协同运动问题。虽然协同运动被认为对所有玻璃化转变附近的液体动力学都很重要，但聚合物为探索协同运动提供了一些独特的机会。Monte Carlo和分子动力学模拟将被用来直接测量合作放松区域的大小和形状的分布，重点是确定可以应用于真实的实验的措施。介电实验测量可混溶聚合物共混物中链段弛豫时间的分布将用于估计每个共混组分的协同尺寸的温度依赖性。系统地改变聚合物结构（链长和侧基）的实验也将提供单组分聚合物熔体中协同尺寸对温度依赖性的不太直接的测量。流变学实验和分子动力学模拟将探索链段动力学和链动力学之间的联系，并行研究。这种连接将使我们的模型在可调共混物链段动力学扩展到预测终端动态，包括共混物粘度，没有额外的参数。这项研究的智力价值将是提高对聚合物及其混溶共混物动力学的理解，特别强调协同运动的作用以及链段和链动力学之间的联系。 拟议研究的更广泛影响有三个方面。一方面，混溶共混物流变学模型将在塑料工业中找到直接的实用用途，其中聚合物共混物对于塑料回收和运输工业中的金属替代是至关重要的。后者能够在不牺牲强度的情况下减轻重量，从而节省燃料。同时，对协同运动的理解将对发展对液态动力学的理解产生深远的影响，而这种理解远远超出了聚合物。最后，本研究将为研究生和本科生创造学习机会。除了本科生和研究生参与实验研究之外，PI还广泛利用他们不断增长的聚合物物理学知识，在本科生和研究生层面进行招聘，咨询和教学。

Cooperative motion is widely accepted as being important for dynamics of glass-formingliquids, yet the length scales over which cooperative motion occurs are poorly understood.Experiments are proposed and computer simulations to address cooperative motion in polymers.While cooperative motion is thought to be important for the dynamics of all liquidsnear their glass transition, polymers o.er some unique opportunities for probing cooperativemotion. Monte Carlo and Molecular Dynamics simulations will be utilized to directly measurethe distribution of sizes and shapes of cooperatively relaxed regions, with an emphasison determining measures that can be applied to real experiments. Dielectric experimentsmeasuring the distribution of segmental relaxation times in miscible polymer blends willbe used to estimate the temperature dependence of the cooperative size, for each blendcomponent. Experiments that systematically vary polymer structure (chain length and sidegroups) will also provide less direct measures of the temperature dependence of cooperativesize in single-component polymer melts. Rheology experiments and Molecular Dynamicssimulations will explore the connection between segmental dynamics and chain dynamics, inparallel studies. This connection will allow our models for segmental dynamics in miscibleblends to be extended to predict the terminal dynamics, including the blend viscosity, withno additional parameters. The intellectual merit of this research will be an improved understandingof dynamics in polymers and their miscible blends, with particular emphasis onthe role of cooperative motion and the connection between segmental and chain dynamics. The broader impacts of the proposed research are threefold. On the one hand, the modelof miscible blend rheology will find immediate pragmatic use in the plastics industry, wherepolymer blends are vital for plastics recycling and for metals replacement in the transportationindustry. The latter enables weight to be reduced without sacrificing strength, therebysaving fuel. Simultaneously, understanding of cooperative motion will have far-reachingconsequences in developing an understanding of liquid state dynamics that goes far beyondpolymers. And finally the proposed research will create learning opportunities for graduateand undergraduate students. In addition to the involvement of both undergraduate andgraduate students in the experimental research, the PIs make extensive use of their growingknowledge of polymer physics in recruiting, advising and teaching at both the undergraduateand graduate levels.