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

9818585施拉格拟议的实验研究将探索稀溶液聚合物动力学测量在远高于玻璃化转变温度的温度下检测和表征玻璃形成溶剂中动态空间异质性的可能性。初步数据表明，这些空间非均质性可能控制了短时间聚合物动力学。拟议的研究大致分为三个类别。首先，将进行测量，以便能够将最初在玻璃形成溶剂(稀溶液条件)中的几种聚合物的驰豫时间谱宽度与相同聚合物作为未纠缠熔体的驰豫时间谱宽度进行比较。(初步数据表明，这两种聚合物有很大的不同：一种给定的聚合物似乎在熔融状态下更具弹性。)其次，最短的聚合物弛豫时间以及溶剂液的有效粘度将被确定为聚合物相对分子质量(低M)和浓度的函数，适用于尽可能多的不同聚合物/玻璃形成液组合，只要时间、仪器限制和人员允许。第三，考察相同稀溶液的时间-温度叠加参数和有效高频振荡流动双折射和/或粘弹性性质作为聚合物相对分子质量(低M)和浓度的函数，将提供关于这些液体中表观动态非均质性的空间维度的额外重要信息。上述链条动力学信息将从采用独特定制仪器的振荡流动双折射和/或粘弹性研究中获得。综上所述，可以对玻璃形成液体的关联长度和关联寿命提供合理的估计--希望还有它们与温度的关系。%这些研究应该确定从聚合物溶液的动力学研究中获得的表观“聚合物柔性”是否实际上反映了溶剂中的动态空间非均质性。如果是这样的话，正如非常初步的结果所表明的那样，它应该提供一种简单和方便的方法来获得此类液体的“簇大小”和“簇寿命”，并可能导致对聚合物添加剂在润滑油和机油中的作用的更好的理解，从而能够开发出显著改进的产品。此外，对于具有大量短支化的聚合物，通过链动力学传感实验可以显著改善支化特性。这项工作将是针对聚合物化学专业研究生的毕业论文研究。

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.***