Kinetic Control of Polymer Nanostructure in Lyotropic Liquid Crystalline Systems

项目摘要：自组织液晶是实现有机聚合物在纳米尺度上的结构和化学控制以增强其性能的一种手段。最近受到极大关注的一个领域是基于溶致性（即两亲性）液晶（llc）的功能纳米结构聚合物材料的开发，这种材料具有在水存在下自组织成具有周期性纳米级多孔结构域的有序组装的能力。最近，LLC单体聚合和LLC模板聚合物在固态有机催化剂、尺寸选择膜和组织工程支架等应用中都显示出巨大的前景。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，在聚合过程中，热力学驱动的相分离发生，留下很少或没有液晶秩序。LLC体系中的聚合动力学高度依赖于有序，但聚合速率与最终聚合物纳米结构之间的直接关系尚未得到探讨。智力优势：本研究的目标是利用光聚合的速度来预测和控制LLC系统中产生的纳米结构。研究将集中于形成LLC相的活性表面活性剂单体，以及由非活性LLC模板化的极性和非极性单体。材料的光聚合跨越大范围的LLC相将被监测，以了解在聚合过程中发生的变化。影响聚合物形态的因素包括LLC相结构和稳定性、交联密度、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，从而允许对热力学上不利的聚合物纳米结构进行动力学捕获。将研究由传统的链式和巯基步长聚合形成的聚合物的机理。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）来阐明聚合物结构。光聚合动力学和双键转化将使用光差扫描量热法、红外和拉曼光谱进行实时监测。获得的结果将有助于建立一个完整的模型，概述控制最终聚合物纳米结构的动力学和热力学因素。更广泛的影响：最近对纳米技术的重视可能带来的最有希望的进步之一是能够控制有机聚合物中基于纳米级结构的特性。这项工作提出了基于LLC几何形状的可重复生产纳米结构的方法，利用固有的光聚合速度，允许基于纳米几何形状控制聚合物性质。如果这种控制能够实现，分离技术、水凝胶和组织工程等应用领域将取得实质性进展。一个普遍的主题将是学生教育。将强调本科生和研究生研究人员在发现学习环境中的广泛参与。PI在研究生和本科阶段都有包括少数民族学生研究人员的良好记录。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夏季研究计划的一部分。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展示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.