Dynamics of Block Copolymer Micelles

非技术综述：胶束是由洗涤剂和脂类等两亲性分子自发组装形成的纳米级物体。被称为嵌段共聚物(BCP)的较大的两亲分子采用类似的结构，但通常对机械力或化学环境的变化更具健壮性。出于这些原因，BCP胶束在各种新兴技术中发挥着越来越重要的作用，包括作为合成机油的粘度改进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。在这些应用中，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，分子经过精心设计以产生预期的结构。然而，一个根本的问题是理解自组装机制本身。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、平衡的结构，或者系统是否已经陷入了非最佳的所谓的亚稳状态。在后一种情况下，胶束是通过什么机制演变成更有利的状态的？有了这些知识，就有可能在尽可能短的时间内定制特定的商业过程，以可靠和可重复的方式生产最有用的纳米结构。研究生将在聚合物合成和表征、光、X射线和中子散射以及电子显微镜方面获得广泛的技能。他们还将有广泛的机会向外部观众介绍技术演讲和海报，以及指导有才华的本科生。来自大双子城的高中生，特别是女性和代表性不足的少数族裔，将通过“聚合物日：你做到了，你打破了它”接触到聚合物科学，这是一个更广泛的“发现STEM：材料周”夏令营的实践部分。来自全国各地的不同的研究生和博士后研究员将参加未来教师研讨会，以提高获得学术职位并取得成功的技能。技术摘要：虽然嵌段共聚物(BCP)胶束的平衡结构相对较好地被理解，但这种结构演变的动态过程还不是很清楚。此外，通过溶液自组装形成的BCP胶束通常处于亚稳态、非平衡态。描述了一个全面的实验计划，旨在发展对控制嵌段共聚聚合物胶束自组装的五个分子水平过程的定量理解。这些过程包括胶束碎裂和融合，以前的研究非常少。理解单链交换的顽固问题将通过计算机模拟来解决，而在理解胶束产生和湮灭的能量障碍的影响方面的悬而未决的问题将使用相同的模型聚合物系统来解决。将使用一套强大的实验工具，特别是动态光散射、小角X射线和中子散射以及液体透射电子显微镜。结果将提供对现有模型的关键测试，或将提供基准数据集，为未来的理论发展提供参考。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.