Shape Changing Stimuli-Responsive Multicomponent Molecular Bottlebrushes in Solution and at Interfaces

分子瓶刷聚合物是一类由非常长的聚合物主链和密集接枝的较短分子组成的链状分子。这些聚合物表现出有趣的特性，可以用于制造先进材料，减少摩擦的润滑，药物的药物输送。它们的形状由主链和侧链的长度比以及侧链与自身和环境的相互作用决定。外界刺激已被证明可以触发刷状聚合物的形状变化，从蠕虫状到球形，模仿天然蛋白质的折叠和展开行为。在这个项目中，PI将设计，制备和研究多组分刷聚合物，这些聚合物可以在外部刺激的应用下单独改变溶液和界面的形状。对这种大分子在各种条件下的性质和行为的基本理解将潜在地影响许多技术，包括物质（如药物）的靶向递送和对环境敏感的泡沫和乳液。该研究项目将为培养博士后研究人员、研究生和本科生提供一个平台，因此将在研究本身之外产生更广泛的社会影响。外展活动旨在激发高中生对STEM领域的兴趣，拓宽田纳西大学诺克斯维尔分校学生的科学视野。本项目旨在合成多组分分子瓶刷聚合物，该聚合物可以在响应外部刺激时显示形状变化，并了解各种分子参数如何影响其在稀和中浓溶液和界面中的形状变化行为。具体而言，该研究项目将利用先前开发的合成策略，通过最先进的合成技术制备刺激响应的多组分刷状聚合物，表征其分子尺寸和构象（形状）的变化，在稀和中等浓度的水溶液中，在外场下和界面处施加外部刺激，阐明各种分子参数对形状改变行为的影响。揭示了电刷聚合物在不同条件下的独特性能。将制备一系列具有不同化学组成、分子量、分子结构和窄分散度的多组分瓶刷聚合物。他们将通过多检测器尺寸排除色谱（SEC）来研究分子量和尺寸，动态和静态光散射（DLS和SLS）来研究不同条件下的分子大小，原子力显微镜（AFM）和透射电子显微镜（TEM）来直接观察衬底，以及小角中子散射（SANS）来原位研究溶液中的刷子尺寸和构象。从该研究项目中获得的知识将用于指导功能刷聚合物的设计和合成，用于输送物质和刺激响应泡沫和乳液的潜在应用。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知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYMolecular bottlebrush polymers are a class of chain-like molecules composed of a very long polymer backbone with densely grafted shorter molecules. These polymers exhibit intriguing properties and could be used, e.g., in manufacture of advanced materials, lubrication for friction reduction, drug delivery for medication. Their shapes are governed by the length ratio of backbone and side chains and the interactions of side chains with themselves and their environment. External stimuli have been shown to trigger the shape change of brush polymers from wormlike to globular, which mimics the folding and unfolding behavior of natural proteins. In this project the PI will design, prepare, and study multicomponent brush polymers that can individually change their shapes in solutions and at interfaces upon application of external stimuli. The fundamental understanding of the properties and behavior of such giant molecules under various conditions will potentially impact many technologies, including targeted delivery of substances (e.g., medications) and environmentally responsive foams and emulsions. The research program will provide a platform for training postdoctoral researchers, graduate and undergraduate students, and thus will have broader societal impact beyond the research itself. Outreach activities will be directed to stimulate the interest of high school students toward STEM fields and to broaden the science horizons of the students at the University of Tennessee Knoxville.PART 2: TECHNICAL SUMMARYThis project is aimed at synthesizing multicomponent molecular bottlebrush polymers that can display shape changes in response to external stimuli and understanding how various molecular parameters affect their shape changing behavior in dilute and moderately concentrated solutions and at interfaces. Specifically, the research program will utilize previously developed synthetic strategies to prepare stimuli-responsive multicomponent brush polymers via state-of-the-art synthesis techniques, characterize their changes in molecular dimension and conformation (shape) upon application of external stimuli in dilute and moderately concentrated aqueous solution, under external fields, and at interfaces, elucidate the effects of various molecular parameters on shape-changing behavior, and reveal the unique properties of brush polymers under different conditions. A series of multicomponent molecular bottlebrush polymers with various chemical compositions, molecular weights, molecular architectures, and narrow dispersities will be made. They will be investigated by multidetector size exclusion chromatography (SEC) for molecular weights and dimensions, dynamic and static light scattering (DLS and SLS) for molecular sizes under different conditions, atomic force microscopy (AFM) and transmission electron microscopy (TEM) for direct visualization on substrates, and small angle neutron scattering (SANS) for in situ study of brush dimensions and conformations in solutions. The knowledge gained from this research project will be used to guide the design and synthesis of functional brush polymers for potential applications in delivery of substances and stimuli-responsive foams and emulsions.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.