Dynamics of Multicomponent Polymers

这项研究的目的是从根本上了解动态过程-扩散，粘度，粘弹性-在任何含有一个以上的化学重复单元的聚合物材料。 这类多组分聚合物。 包括可混溶和不可混溶的共混物、无规和嵌段共聚物以及它们的混合物的一类。 在现代高分子科学技术中无处不在。单组分聚合物动力学的描述已经有了相当大的进展，主要是通过基于爬行的模型，但扩展到多组分系统落后。有两个主要的障碍：（一）有限的理解的组成和温度依赖性的局部链段动力学的基础上的所有机制的链松弛，和（ii）不完全理解的混合链动力学的机制的影响。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。 智力优势 最近的研究揭示了各种有趣的现象，在二元聚合物混合物的动力学，归因于这两个组件的链段迁移率的温度依赖性是不同的。 这种“热流变复杂性”既源于柔性的内在差异，分子内的贡献，也源于块体、平均组成和片段周围局部环境之间的差异。 对这些观察结果的部分解释是基于自我集中的想法，即仅仅由于链连接性而使环境中的类似单体局部富集，已经证明能够描述大部分现象。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具启发性的未来实验。 这三种实验技术相结合，将允许精确提取的动态的每一个组成部分，在精心挑选的模型共混物，在广泛的组成和温度范围。这些数据应该能够充分描述当地动态，这反过来又将指导改进的预测模型的开发。然后，通过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，在相同的模型共混物的组合物和温度依赖性粘度的测量将允许详细测试所提出的模型，如“双爬行”，多分散性对链动力学的影响。此外，提取的全频率依赖的响应和扩散的混合物中的稀释组分将导致长期存在的“约束释放与轮廓长度波动”的争议在线性粘弹性的实验解决方案。更广泛的影响 绝大多数商业聚合物材料都是在液态下加工的，其中粘弹性响应（线性和非线性）最终决定了什么可以做，什么不能做。随着可被认为是“多组分”的商业材料的比例稳步增加，“相关”（即， 获取所观察到的并将其与分子变量相关联）和“预测”（即，基于分子变量预测性质）方案也在增长。本文所述的研究表明，提供了第一个可靠的预测方案的混溶性聚合物共混物的粘度的承诺。 此外，基本的概念应有助于预测计划的粘弹性的其他多组分系统，并在长期运行的非线性流动特性以及。 该计划整合了聚合物科学的全方位教学和研究。 合成、表征、形态学、流变学、动力学和理论。 为化学、化学工程和材料科学专业的学生提供。这种培训的广度使集团校友在学术和工业环境中具有吸引力，并对传统聚合物行业以外的公司具有吸引力。 指导本科生的定期机会，并在国家科学会议上展示研究成果，并向工业科学家的观众，构成了该计划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.