Dynamics of Block Copolymer Micelles

非技术概述：胶束是由两亲性分子（如洗涤剂和脂类）自发组装而成的纳米级物体。较大的两亲化合物嵌段共聚物（bcp）采用类似的结构，但通常对机械力或化学环境变化的抵抗力更强。由于这些原因，BCP胶束在各种新兴技术中越来越重要，包括作为合成机油的粘度调节剂以提高燃油经济性，以及作为将治疗剂输送到特定靶细胞（如癌症）的载体。在这些以及更多的应用中，纳米结构是通过“自下而上”的自组装过程产生的，通过这种自组装过程，分子被精心设计以产生预期的结构。然而，一个根本的问题是了解自组装本身的机制。特别是，重要的是要知道所得到的纳米结构是否是最有利的，平衡的，或者系统是否已经陷入了一个非最佳的所谓的“亚稳态”状态。在后一种情况下，这是很常见的，胶束通过什么机制向更有利的状态演化？有了这些知识，就有可能定制一个给定的商业过程，在尽可能短的时间内生产出最有用的、可靠的、可复制的纳米结构。研究生将获得聚合物合成和表征，光，x射线和中子散射以及电子显微镜方面的广泛技能。他们还将有广泛的机会向外部观众发表技术演讲和海报，以及指导有才华的本科生。来自双子城的高中生，尤其是女性和少数族裔，将通过“聚合物日：你创造它，你打破它”来接触聚合物科学，这是一个更广泛的“发现STEM：材料周”夏令营的实践组成部分。来自全国各地的研究生和博士后将参加未来教师研讨会，以提高获得学术职位和取得成功的技能。技术概述：虽然嵌段共聚物（BCP）胶束的平衡结构相对较好理解，但这种结构演变的动态过程尚不清楚。此外，由溶液自组装形成的BCP胶束经常被困在亚稳态，非平衡状态。本文描述了一个全面的实验程序，旨在对被认为控制嵌段共聚物胶束自组装的五个分子水平过程进行定量理解。这些过程包括胶束破碎和融合，这方面的研究非常少。在理解单链交换方面的顽固性问题将通过计算机模拟来解决，而在理解能量障碍对胶束产生和湮灭的影响方面的未解决问题将使用相同的模型聚合物系统来解决。将采用一套强大的实验工具，特别是动态光散射，小角度x射线和中子散射，以及液相透射电子显微镜。研究结果将为现有模型提供关键测试，或为未来的理论发展提供基准数据集。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARY: Micelles are nanoscale objects formed by spontaneous assembly of amphiphilic molecules such as detergents and lipids. Larger amphiphiles known as block copolymers (BCPs) adopt analogous structures, but typically are much more robust against mechanical forces or changes in chemical environment. For these reasons, BCP micelles are of growing importance in a variety of emerging technologies, including as viscosity modifiers in synthetic motor oils to boost fuel economy, and as vehicles for delivery of therapeutic agents to specific target cells, such as cancers. In 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 is to understand the mechanism of self-assembly itself. In particular, it is important to know whether the resulting nanostructure is the most favorable, equilibrium one, or whether the system has become trapped in a non-optimal so-called “metastable” state. In the latter case, which is quite common, by what mechanisms do micelles evolve toward a more favorable state? With this knowledge, it will be possible to tailor a given commercial process to produce the most useful nanostructure, reliably and reproducibly, in the shortest possible time. Graduate students will acquire a broad suite of skills in polymer synthesis and characterization, light, X-ray and neutron scattering, and electron microscopy. 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: Materials Week" summer camp. A diverse cohort of graduate students and postdoctoral fellows from across the country will participate in Future Faculty Workshops, to enhance skills in acquiring and succeeding in academic positions.TECHNICAL SUMMARY: While the equilibrium structure of block copolymer (BCP) micelles is relatively well understood, the dynamic processes by which such structures evolve are not. Furthermore, BCP micelles formed by solution self-assembly are often trapped in metastable, non-equilibrium states. A comprehensive experimental program is described, aimed at developing a quantitative understanding of the five molecular-level processes believed to control block copolymer micellar self-assembly. These processes include micellar fragmentation and fusion, for which prior studies are very scarce. Recalcitrant problems in understanding single chain exchange will be attacked with computer simulations, and unresolved issues in understanding the effect of energetic barriers to micelle creation and annihilation will be addressed using the same model polymer systems. A suite of powerful experimental tools will be employed, especially dynamic light scattering, small-angle X-ray and neutron scattering, and liquid-phase transmission electronic microscopy. The results will provide critical tests of existing models, or will provide benchmark data sets to inform future theoretical developments..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.