Dynamics of Multicomponent Polymers

这项研究旨在对任何含有一个以上化学重复单元的聚合物材料的动态过程——扩散、粘度、粘弹性——有一个基本的理解。这种多组分聚合物。包括混相和非混相共混物、无规共聚物和嵌段共聚物及其混合物的一类。在现代大分子科学技术中无处不在。单组分聚合物的动力学描述已经取得了相当大的进展，主要是通过基于声誉的模型，但扩展到多组分系统滞后。有两个主要的障碍：(i)对所有链弛豫机制下的局部节段动力学的组成和温度依赖性的理解有限；（ii）对混合对链动力学机制的影响的理解不完全。拟议的研究将通过对模型系统的战略测量来解决这两个问题，使用三种强大技术的独特组合：流变学，振荡流双折射和扩散。最近的研究揭示了二元聚合物混合物动力学中各种令人着迷的现象，这是由于这两种组分的节段迁移率对温度的依赖是不同的。这种“热流变复杂性”既源于柔韧性的内在差异、分子内贡献，也源于体积、平均组成和部分周围局部环境之间的差异。对这些观察结果的部分解释基于自集中的概念，即由于链连通性而使环境在类似单体中局部富集，已被证明能够描述许多现象学。此外，它提供了一个组织原则，通过它可以对各种系统的行为进行分类，并强调了那些可能最有启发性的未来实验。这三种实验技术的结合将允许在广泛的成分和温度范围内，在精心选择的模型混合物中精确提取每个成分的动力学。这些数据应该能够充分描述局部动态，从而指导改进的预测模型的发展。然后，随着对局部动力学的理解，将有可能通过相同的实验方案解决有关链动力学的几个长期存在的问题。特别是，对同一模型混合物的组成和温度依赖粘度的测量将允许对所提出的模型进行详细的测试，例如“双重重复”，以研究多分散性对链动力学的影响。此外，提取混合物中稀组分的全频率相关响应和扩散系数将导致线性粘弹性中长期存在的“约束释放与轮廓长度波动”争议的实验解决。绝大多数商用高分子材料都是在液态下加工的，其中的粘弹性响应（线性和非线性）最终决定了什么可以做，什么不可以做。随着被认为是“多组分”的商业材料的比例稳步增加，“相关”（即，将观察到的东西与分子变量联系起来）和“预测”（即，基于分子变量预测性能）方案的重要性和实用性也在增长。本文所描述的研究有望为可混相聚合物共混物的粘度提供第一个可靠的预测方案。此外，基础概念应该有助于其他多组分系统的粘弹性预测方案，以及从长远来看，非线性流动特性也是如此。该项目将高分子科学的教学和研究结合在一起。合成，表征，形态，流变学，动力学和理论。适用于化学、化学工程和材料科学专业的学生。这种广泛的培训使集团校友在学术和工业环境以及远远超出传统聚合物行业的公司中都具有吸引力。定期有机会指导本科生，并在国家科学会议和工业科学家的听众中展示研究成果，构成了该项目研究生教育的重要组成部分。

This research is aimed at a fundamental understanding of dynamic processes - diffusion, viscosity, viscoelasticity - in any polymer material containing more than one chemical repeat unit. Such multicomponent polymers . a class that includes miscible and immiscible blends, random and block copolymers, and their mixtures . are ubiquitous in modern macromolecular science and technology. Description of the dynamics of single component polymers has advanced considerably, primarily via reptation-based models, but the extension to multicomponent systems lags behind. There are two main obstacles: (i) limited understanding of the composition and temperature dependence of the local segmental dynamics that underly all mechanisms of chain relaxation, and (ii) incomplete understanding of the effects of mixing on the mechanisms of chain dynamics. The proposed research will address both of these issues through strategic measurements on model systems, using a unique combination of three powerful techniques: rheology, oscillatory flow birefringence, and diffusion. Intellectual Merit Recent research has revealed a variety of fascinating phenomena in the dynamics of binary polymer mixtures, attributable to the fact that the temperature dependences of the segmental mobilities of the two components are distinct. This "thermorheological complexity" arises both from intrinsic differences in flexibility, an intramolecular contribution, and from differences between the bulk, average composition, and that of the local environment surrounding a segment. A partial explanation for these observations based on the idea of self-concentration, the local enrichment of the environment in like monomers due simply to chain connectivity, has proven capable of describing much of the phenomenology. Furthermore, it provides an organizing principle by which the behavior of various systems can be classified, and it highlights those future experiments that are likely to be most revealing. The three experimental techniques in combination will allow precise extraction of the dynamics of each component, in carefully selected model blends, over broad ranges of composition and temperature. These data should enable full characterization of the local dynamics, which in turn will direct the development of an improved, predictive model. Then, with an understanding of local dynamics in hand, it will be possible to address several longstanding issues concerning chain dynamics, via the same experimental protocol. In particular, measurements of the composition and temperature dependent viscosity on the same model blends will allow detailed testing of proposed models, such as "double reptation", for the effects of polydispersity on chain dynamics. Furthermore, the extraction of the full frequency dependent response and diffusivity of a dilute component in a mixture will lead to an experimental resolution of the longstanding "constraint release versus contour length fluctuations" controversy in linear viscoelasticity. Broader Impact The vast majority of commercial polymer materials are processed in the liquid state, where the viscoelastic response (both linear and non-linear) ultimately dictates what can and can't be done. As the fraction of commercial materials that may be considered "multicomponent" increases steadily, the importance and utility of both "correlative" (i.e., take what is observed and relate it to molecular variables) and "predictive" (i.e., predict properties based on molecular variables) schemes grows as well. The research described herein shows promise of providing the first reliable predictive scheme for the viscosity of a miscible polymer blend. Furthermore, the underlying concepts should contribute to predictive schemes for the viscoelasticity of other multicomponent systems, and in the longer run for the non-linear flow properties as well. This program integrates teaching and research over the full range of polymer science . synthesis, characterization, morphology, rheology, dynamics, and theory . for students in chemistry, chemical engineering, and materials science programs. This breadth of training has made group alumni attractive in both academic and industrial settings, and to companies extending well beyond the traditional polymer industry. Regular opportunities for mentoring undergraduates, and for presenting research results at national scientific meetings and to audiences of industrial scientists, constitute an essential component of graduate student education in this program.