From Micelles to Membranes: Advanced Block Polymer Ionic Liquid Composites

技术概要：本项目的目标是通过将离子液体与嵌段共聚物相结合来推进一类新的功能性纳米结构材料。离子液体表现出许多吸引人的性质，包括化学和热稳定性、消失的蒸气压、可调的溶剂化、高离子电导率和高介电常数，这使得它们作为潜在的“绿色”溶剂以及作为塑料电子器件、电池、燃料电池、气体分离膜和致动器中的关键成分而吸引人。为了在先进材料应用中实现这些性质，有必要固化材料，和/或将离子液体限制在所需的纳米结构内。嵌段共聚物提供了前所未有的灵活性，可以在1-100纳米的长度范围内直接自组装，同时提供机械完整性。三个不同的子项目设想，解决聚合物材料科学的基本问题，每个利用纳米结构的共聚物/离子液体混合物的一个独特的方面。首先，将建立一个定量的了解在嵌段共聚物胶束的链交换率，利用时间分辨小角中子散射同位素标记的胶束混合物。凭借离子液体的宽的可用温度范围，以及临界胶束化温度可以通过共混同源咪唑阳离子可预测地调节的容易性，将系统地描绘从“遍历性”到“非遍历性”的交叉。其次，最近发现的离子液体填充囊泡分散在水中将扩展到纳米反应器的应用，从而催化剂被限制在囊泡内部，并可以很容易地回收。水性基质减轻了离子液体反应介质的严重成本和传质限制，而囊泡膜将调节反应物和产物在水相和离子液体相之间分配的速率。最后，ABC三嵌段聚合方法被提出来制备具有导电性的、富含离子液体的纳米通道的交联的双和三连续膜，其目标是获得前所未有的高机械韧性和离子电导率的组合。非技术概要：由聚合物和室温离子液体制备的复合材料正在积极考虑用于许多先进技术，包括生物质改性、气体分离膜、塑料电子、离子电池和燃料电池。任何一个领域的成功都将在节能、可持续塑料和便携式储能方面产生深远的社会影响。 同时优化不同的性能，如高离子传输，机械完整性和易于加工，可以最好地通过在纳米尺度上的结构控制来实现。因此，结构导向嵌段共聚物与功能化离子液体的结合将加速先进材料的发展。研究生将获得聚合物合成和表征，光，X射线和中子散射，荧光光谱和电子显微镜的广泛技能。他们还将有广泛的机会向外部观众展示技术讲座和海报，以及指导有才华的本科生进行研究。来自双子城的高中生，特别是女性和代表性不足的少数民族，将通过“聚合物日：你制造它，你打破它”接触聚合物科学，这是一个更广泛的“探索科学工程职业”夏令营的实践部分。

TECHNICAL SUMMARY:The goal of this project is to advance a new class of functional nanostructured materials by combining ionic liquids with block copolymers. Ionic liquids exhibit many appealing properties, including chemical and thermal stability, vanishing vapor pressure, tunable solvation, high ionic conductivity, and high dielectric constant, that render them appealing as potential 'green' solvents, and as key ingredients in plastic electronics, batteries, fuel cells, gas separation membranes, and actuators. To realize these properties in advanced materials applications, it is necessary to solidify the material, and/or to confine the ionic liquid within a desired nanostructure. Block copolymers offer unprecedented flexibility to direct self-assembly over lengthscales from 1-100 nanometers, while simultaneously providing mechanical integrity. Three different sub-projects are envisioned that address fundamental issues in polymer materials science, and each exploits a unique aspect of nanostructured copolymer/ionic liquid mixtures. First, a quantitative understanding of the rate of chain exchange in block copolymer micelles will be established, by utilizing time-resolved small-angle neutron scattering on isotopically labeled micelle mixtures. By virtue of the wide usable temperature range of ionic liquids, and the ease with which critical micellization temperatures can be tuned predictably by blending homologous imidazolium cations, the crossover from 'ergodicity' to 'non-ergodicity' will be delineated systematically. Second, the recent discovery of ionic-liquid-filled vesicles dispersed in water will be extended to nanoreactor applications, whereby the catalyst is confined to the vesicle interior, and may be recovered easily. The aqueous matrix mitigates the severe cost and mass transfer restrictions of ionic liquid reaction media, while the vesicle membrane will regulate the rate of reactant and product partitioning between aqueous and ionic liquid phases. Last, an ABC triblock terpolymer approach is proposed to prepare crosslinked bi- and tri-continuous membranes with conductive, ionic-liquid-rich nanochannels, with the goal of accessing unprecedented combinations of high mechanical toughness and ionic conductivity.NON-TECHNICAL SUMMARY:Composite materials prepared from polymers and room temperature ionic liquids are under active consideration for many advanced technologies, including biomass modification, gas separation membranes, plastic electronics, ion batteries, and fuel cells. Success in any of these areas would have profound societal impact in terms of energy conservation, sustainable plastics, and portable energy storage. Simultaneous optimization of diverse properties, such as high ionic transport, mechanical integrity, and facile processing, can best be achieved through structural control at the nanometer scale. Thus, the combination of structure-directing block copolymers and functional ionic liquids will accelerate the development of advanced materials. Graduate students will acquire a broad suite of skills in polymer synthesis and characterization, light, x-ray and neutron scattering, fluorescence spectroscopy, 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 in research. 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 "Exploring Careers in Science & Engineering" summer camp.