Kinetic Control of Polymer Nanostructure in Lyotropic Liquid Crystalline Systems

Allan Guymon研究所：爱荷华大学提案编号：0626395题目：溶致液晶系统中聚合物纳米结构的动力学控制项目摘要：使用自组织液晶是在纳米尺度上实现有机聚合物的结构和化学控制以提高性能的一种手段。最近引起人们极大兴趣的一个领域是基于溶致(即两亲性)液晶(LLC)的功能纳米结构聚合物材料的开发，这些LLC能够在水存在下自组织成具有周期性纳米尺度多孔域的有序组装。近年来，聚合LLC单体和以LLC为模板的聚合物在固体有机催化剂、尺寸选择膜和组织工程支架等方面显示出巨大的应用前景。使用聚合LLC材料的主要障碍是在整个聚合过程中保持和控制这种结构的能力。通常，热力学驱动的相分离发生在聚合过程中，很少或没有液晶有序。LLC体系中的聚合动力学高度依赖于有序性，但聚合速率和最终聚合物纳米结构之间的直接关系尚未被探索。智能优点：本研究的目标是利用光聚合速度来预测和控制LLC体系中产生的纳米结构。研究将集中在形成LLC相的反应性表面活性剂单体以及以非反应性LLC为模板的极性和非极性单体。将监测跨越各种LLC相的材料的光聚合，以了解聚合过程中发生的变化。可能影响聚合物形态的因素包括LLC相结构和稳定性、交联剂密度、单体极性和双键位置。自由基光聚合提供了在很宽的温度范围内在几分之一秒内聚合的能力，从而允许动力学捕获原本在热力学上不利的聚合物纳米结构。我们将研究由传统链状和硫醇-烯阶梯生长聚合机理形成的聚合物。由于纳米结构在本项目中的重要性，将使用一些强大的表征工具(偏振光显微镜、X射线衍射和扫描电子显微镜)来阐明聚合物的结构。利用光差示扫描量热法、红外光谱和拉曼光谱对光聚合动力学和双键转化进行实时监测。所获得的结果将有助于开发一个完整的模型，概述控制最终聚合物纳米结构的动力学和热力学因素。广泛影响：最近对纳米技术的重视可能导致的最有希望的进展之一是能够控制基于有机聚合物产生的纳米级结构的性能。这项工作提出了基于LLC几何形状的方法，利用固有的光聚合速度来重复生产纳米结构，从而允许基于纳米尺度几何形状来控制聚合物的性质。如果能够实现这种控制，就可以在分离技术、水凝胶和组织工程等各种应用方面实现实质性的进步。一个流行的主题将是学生教育。将强调本科生和研究生在发现学习环境中的广泛参与。国际和平研究所在包括研究生和本科生在内的少数民族学生研究人员方面有着很好的记录。至少有一名少数族裔研究生将直接参与拟议的研究，少数族裔本科生研究人员将被招募为爱荷华大学AGEP暑期研究计划的一部分。此外，聚合物在纳米技术中的重要性将作为PI在当地和农村高中化学课上介绍的模块的一部分带给高中生。

ABSTRACTPI: Allan Guymon Institution: University of IowaProposal Number: 0626395Title: Kinetic Control of Polymer Nanostructure in Lyotropic Liquid Crystalline SystemsProject Summary: The use of self-organizing liquid crystals is a means of achieving structural and chemical control of organic polymers on the nanometer scale for enhanced performance. One area that has recently received a great deal of interest is the development of functional nanostructured polymer materials based on lyotropic (i.e., amphiphilic) liquid crystals (LLCs) which have the ability to self organize in the presence of water into ordered assemblies with periodic nanometer-scale porous domains. Both polymerized LLC monomers and polymers templated by LLCs have recently shown great promise in applications such as solid-state organic catalysts, size-selective membranes, and tissue engineering scaffolds. The major obstacle in using polymerized LLC materials is the ability to retain and control this structure throughout the polymerization. Typically, thermodynamically driven phase separation occurs during polymerization, leaving little or no liquid crystalline order. The polymerization kinetics in LLC systems are highly dependent on order, but the direct correlation between the polymerization rate and ultimate polymer nanostructure has not been explored.Intellectual Merit: The goal of this research is to use the speed of photopolymerization to predict and control the nanostructure produced in LLC systems. Research will focus on reactive surfactant monomers that form LLC phases and both polar and non-polar monomers templated by nonreactive LLCs. The photopolymerization of materials spanning a wide range of LLC phases will be monitored to understand changes that occur during polymerization. Factors that may influence polymer morphology including LLC phase structure and stability, cross-link density, monomer polarity, and double bond location will be examined. Radical photopolymerization provides the ability to polymerize in fractions of a second at a wide range of temperatures, thereby allowing kinetic trapping of otherwise thermodynamically unfavorable polymer nanostructures. Polymers formed from both traditional chain and thiol-ene step growth polymerization mechanisms will be investigated. With the importance of nanostructure in this project, a number of powerful characterization tools (polarized light microscopy, X-ray diffraction, and scanning electron microscopy) will be used to elucidate polymer structure. Photopolymerization kinetics and double bond conversion will be monitored in real-time using photo-differential scanning calorimetry, infra-red and Raman spectroscopy. The results obtained will facilitate development of a complete model outlining the factors, both kinetic and thermodynamic, governing the ultimate polymer nanostructure.Broader Impact: One of the most promising advances that could result with the recent emphasis on nanotechnology is the ability to control properties based on nano-scale architectures produced in organic polymers. This work proposes methods to reproducibly produce nanostructures based on LLC geometries using the inherent speed of photopolymerization allowing control of polymer properties based on nanoscale geometries. If such control can be achieved, substantial advances in applications as diverse as separation technology, hydrogels, and tissue engineering could be realized. A prevailing theme will be student education. Extensive involvement of undergraduate and graduate researchers in a discovery learning environment will be emphasized. The PI has a strong record of including minority student researchers at both the graduate and undergraduate level. At least one minority graduate student will directly participate in the proposed research, and minority undergraduate researchers will be recruited as part of the AGEP Summer Research Program at the University of Iowa. Additionally, the importance of polymers in nanotechnology will be brought to high school students as part of a module presented by the PI to chemistry classes at both local and rural high schools.