Cooperative Dynamics in Polymer Fluids: Melts, Blends, and their Glass Transition

这笔赠款支持开发一种严格的微观方法的理论研究，以描述结构均质但动态非均质聚合物熔体和共混物中的聚合物动力学，作为其化学结构和热力学条件的函数。在分子水平上了解聚合物熔体和共混物的性质对新材料的开发具有重要意义。这项研究是对过去几年前拨款发展的原始方法的扩展，在该方法中，方程被形式化，并研究了未纠缠的聚合物熔体的动力学。第一次，我们能够定量地描述在非纠缠聚乙烯动力学的计算机模拟和实验中观察到的反常动力学的开始。在新的研究中，我们专注于扩展我们的方法来描述动态非均质流体在聚合物熔体、过冷聚合物熔体和聚合物共混物中的运动。动态非均质的存在，随着温度的降低而增大，这似乎是玻璃化转变开始的机制。研究非均相动力学和浓度波动之间的相互作用可能解释结构均匀的聚合物共混物中存在的动力学异常，如时间-温度叠加的破裂。这项研究支持对聚合物体系动态响应的理论研究。开发的理论将填补这些材料描述方面的一个重要空白，应该会有广泛的应用。

This grant supports theoretical research for the development of a rigorous microscopic approach to describe polymer dynamics in structurally homogeneous, but dynamically heterogeneous polymer melts and blends as a function of their chemical structure and of the thermodynamic conditions. The achievement of a molecular level understanding of the properties of polymer melts and blends is relevant for the development of new materials. This research is an extension of the original approach developed over the past few years of the prior grant, where the equations were formalized and the dynamics of unentangled polymer melts were investigated. For the first time, we were able to describe quantitatively the onset of anomalous dynamics observed in computer simulations and experiments of unentangled polyethylene dynamics. For the new research we focus on extending our approach to describe the motion of dynamically heterogeneous fluids in polymer melts, undercooled polymer melts and polymer blends. The presence of dynamical heterogeneities, increasing in size with decreasing temperature, appears to be the mechanism responsible for the onset of the glass transition. A study of the interplay between heterogeneous dynamics and concentration fluctuations is likely to explain the dynamical anomalies present in structurally homogeneous polymer blends, such as the breaking of time-temperature superposition.%%% This grant supports a theoretical investigation of the dynamical response of polymer systems. The theory developed will fill an important gap in the desciption of these materials and should have wide application.***