Exploration of the Potential of Dilute-Solution Polymer Dynamics Measurements for Detection of Dynamic Spatial Heterogeneities in Glass-Forming Solvents

9818585SchragThe拟议的实验研究将探讨稀释溶液聚合物动力学测量的检测和表征的动态空间不均匀性在玻璃形成溶剂中的温度远高于玻璃化转变温度的潜力。 初步数据表明，这些空间的不均匀性可能控制的短时间聚合物动力学。 拟议的研究分为三大类。 首先，将进行测量，以使最初在玻璃形成溶剂（稀溶液条件）中的几种聚合物的弛豫时间谱宽度的比较，与相同的聚合物的弛豫时间谱宽度作为未缠结的熔体。 （初步数据表明存在重大差异：给定的聚合物在熔融形式下似乎更具柔性。 第二，最短的聚合物弛豫时间以及溶剂化液体的有效粘度将作为聚合物分子量（低M）和浓度的函数来确定，对于尽可能多的不同的聚合物/玻璃形成液体组合，只要时间、仪器限制和人员允许。 第三，时间-温度叠加参数和有效的高频振荡流动双折射和/或粘弹性相同的稀释聚合物溶液的聚合物分子量（低M）和浓度的函数的检查将提供额外的重要信息，在这些液体中的表观动态不均匀性的空间尺寸。 上述链动力学信息将从采用独特的定制仪器的振荡流动双折射和/或粘弹性研究中获得。 以上所有的结合在一起，可以为玻璃形成液体的相关长度和相关寿命提供合理的估计，并且希望它们的温度依赖性。这些研究应确定是否明显的“聚合物的灵活性”，从聚合物溶液的动力学研究，实际上是一个动态的空间异质性的溶剂的反映。 如果是的话，正如非常初步的结果所表明的那样，它应该提供一种简单方便的方法来获得这种液体的"簇尺寸"和"簇寿命"，并可能导致对聚合物添加剂在润滑剂和机油中的作用的更好的理解，从而能够开发出实质性改进的产品。 此外，对于具有大量短支链的聚合物，它可以通过链动力学传感实验显著改善支化表征。 本研究将作为高分子化学专业研究生的论文研究。*

9818585SchragThe proposed experimental studies will explore the potential of dilute-solution polymer dynamics measurements for the detection and characterization of dynamic spatial heterogeneities in glass-forming solvents at temperatures well above the glass-transition temperature. Preliminary data suggests that these spatial heterogeneities probably control the short-time polymer dynamics. The proposed studies fall in three general categories. First, measurements will be carried out to enable comparison of the relaxation time spectrum breadths for several polymers initially in glass-forming solvents (dilute-solution conditions), with the relaxation time spectrum breadths for the same polymers as unentangled melts. (Preliminary data suggests that there are major differences: a given polymer appears to be much more flexible in melt form.) Second, the shortest polymer relaxation time, together with the effective viscosity of the solvating liquid, will be determined as functions of polymer molecular weight (low M) and concentration for as many different polymer/glass-forming liquid combinations as time, instrumental limitations, and personnel permit. Third, examination of time-temperature superposition parameters and effective high-frequency oscillatory flow birefringence and/or viscoelastic properties for the same dilute polymer solutions as functions of polymer molecular weight (low M) and concentration will provide additional important information regarding the spatial dimensions of apparent dynamic heterogeneities in these liquids. The above chain dynamics information will be obtained from oscillatory flow birefringence and/or viscoelasticity studies employing unique custom instrumentation. All of the above, taken together, may provide reasonable estimates of correlation lengths and correlation lifetimes- and hopefully their temperature dependences- for glass-forming liquids.%%%These studies should determine whether or not apparent "polymer flexibility" obtained from dynamics studies of polymer solutions is actually a reflection of dynamic spatial heterogeneity in the solvent. If it is, as very preliminary results suggest, it should provide a simple and convenient method for obtaining "cluster size" and "cluster-lifetimes" for such liquids, and may result in a much improved understanding of the role of polymer additives in lubricants and motor oils, enabling the development of substantially improved products. In addition, for polymers with large numbers of short branches, it may markedly improve branching characterization by means of chain-dynamics-sensing experiments. This work will be the thesis research for graduate students specializing in polymer chemistry.***