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

该基金支持理论研究，以发展一种严格的微观方法来描述结构均匀的聚合物动力学，但动态非均匀的聚合物熔体和混合物作为其化学结构和热力学条件的函数。在分子水平上理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获得资助的原始方法的扩展，在那里，方程被形式化，未纠缠聚合物熔体的动力学被研究。第一次，我们能够定量地描述在计算机模拟和实验中观察到的异常动力学的开始。对于新的研究，我们的重点是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。随着温度的降低，尺寸增大的动态非均质性的存在似乎是导致玻璃化转变发生的机制。非均相动力学和浓度波动之间相互作用的研究可能解释结构均相聚合物共混物中存在的动力学异常，例如时间-温度叠加的破坏。该基金支持对聚合物体系动态响应的理论研究。所建立的理论将填补对这些材料描述的重要空白，并应具有广泛的应用价值

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.***