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Mechanisms of Equilibration in Block Copolymer Micelles

嵌段共聚物胶束的平衡机制

基本信息

批准号：
1707578
负责人：
Timothy Lodge
金额：
$ 66万
依托单位：
University of Minnesota-Twin Cities
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-05-01 至 2021-10-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1707578&HistoricalAwards=false
关键词：
Mechanisms Equilibration Block Copolymer Micelles

项目摘要

Non-Technical Summary Nanostructured materials that are formed by a class of extremely large molecules, advanced plastics called block copolymers, are of growing importance in a variety of emerging technologies. Examples include drug-eluting coatings on stents to prevent rejection; viscosity modifiers in synthetic motor oils to boost fuel economy; vehicles for delivery of therapeutic agents to specific cells, such as cancers; membranes to enable lighter weight, non-flammable lithium batteries. In all of these applications, and many more, the nanostructure is created through the "bottom-up" process of self-assembly, whereby the molecules are carefully designed to produce the intended structure. However, a fundamental problem of widespread importance is to understand the process of self-assembly itself. In particular, it is essential to know whether the resulting nanostructure is the most favorable, equilibrium one, or whether in fact the system has become structure-trapped in a so-called "metastable" state. With this knowledge, it will be possible to tailor a commercial process to produce the most useful nanostructure, reliably and reproducibly, in the shortest possible time. Graduate students trained in this project will acquire a broad suite of skills in chemical synthesis and materials characterization. They will also have extensive opportunities to present technical talks and posters to external audiences, as well as to mentor talented undergraduates. High school students from the greater Twin Cities, particularly women and underrepresented minorities, will be exposed to polymer science through Polymer Day: You Make It, You Break It, a hands-on component of a broader Discover STEM week-long summer camp. A new version, American Indian Materials Week, will be developed, to serve to a drastically underrepresented group in STEM fields. Technical Summary It is the overarching goal of this proposal to elucidate the molecular-level mechanisms by which block copolymer nanostructures achieve equilibrium. By focusing primarily on solution assemblies, i.e., micelles, the molecular factors that dictate the barriers to single chain exchange will be quantified, and then collective motions, such as fusion or fragmentation, will be addressed. The cornerstone of the approach is time-resolved small-angle neutron scattering, which provides an unrivaled, quantitative measure of chain exchange kinetics. Collective motions will require additional tools, such as fluorescence. Structural characterization by small-angle X-ray scattering, dynamic light scattering, and cryogenic transmission electron microscopy will also be important. The use of ionic liquid solvents brings multiple advantages, including the ability to tune thermodynamic interactions precisely, the relative ease of designing both UCST and LCST systems, and the remarkably broad accessible temperature range. The research will aim to answer eight questions: (i) What is the functional dependence of chain exchange barriers on quality. (ii) What is the functional dependence on corona block length? (iii) What is the relationship between chain exchange and the relaxation time of an analogous triblock gel? (iv) How does exchange depend on micelle morphology? (v) What factors control the rates of micelle fragmentation and fusion? (vi) How do micelles equilibrate with respect to aggregation number? (vii) How do mixtures of different micelles equilibrate? (viii) How do these barriers evolve with concentration, from dilute systems to melts?

非技术摘要由一类极大分子（称为嵌段共聚物的高级塑料）形成的纳米结构材料在各种新兴技术中变得越来越重要。例子包括支架上的药物洗脱涂层以防止排斥；合成机油中的粘度调节剂可提高燃油经济性；将治疗剂递送至特定细胞（例如癌症）的载体；薄膜可实现重量更轻、不易燃的锂电池。在所有这些应用以及更多应用中，纳米结构都是通过“自下而上”的自组装过程创建的，其中分子经过精心设计以产生预期的结构。然而，一个具有广泛重要性的基本问题是理解自组装过程本身。特别是，必须知道所得的纳米结构是否是最有利的平衡结构，或者系统实际上是否已被结构捕获在所谓的“亚稳态”状态。有了这些知识，就可以定制商业流程，在尽可能短的时间内可靠且可重复地生产最有用的纳米结构。在该项目中接受培训的研究生将获得化学合成和材料表征方面的广泛技能。他们还将有大量机会向外部观众展示技术演讲和海报，并指导有才华的本科生。来自大双城的高中生，特别是女性和代表性不足的少数族裔，将通过聚合物日：你成功了，你打破了它，接触聚合物科学，这是为期一周的更广泛的探索 STEM 夏令营的实践部分。我们将开发一个新版本“美洲印第安人材料周”，为 STEM 领域代表性严重不足的群体提供服务。技术摘要该提案的首要目标是阐明嵌段共聚物纳米结构实现平衡的分子水平机制。通过主要关注溶液组装，即胶束，将量化决定单链交换障碍的分子因素，然后解决集体运动，例如融合或断裂。该方法的基石是时间分辨小角中子散射，它提供了无与伦比的链交换动力学定量测量。集体运动将需要额外的工具，例如荧光。通过小角 X 射线散射、动态光散射和低温透射电子显微镜进行结构表征也很重要。离子液体溶剂的使用带来了多种优势，包括精确调节热力学相互作用的能力、设计 UCST 和 LCST 系统的相对容易性以及非常宽的可访问温度范围。该研究旨在回答八个问题：（i）链交换壁垒对质量的功能依赖性是什么。 (ii) 电晕块长度的函数依赖性是什么？ (iii) 类似三嵌段凝胶的链交换和弛豫时间之间有什么关系？ (iv) 交换如何取决于胶束形态？ (v) 哪些因素控制胶束破碎和融合的速率？ (vi) 胶束如何在聚集数方面达到平衡？ (vii) 不同胶束的混合物如何平衡？ (viii) 这些屏障如何随着浓缩而演变，从稀体系到熔体？