Topological Changes In Associative Polymer Networks Due to Mechanical Stress

机械应力导致缔合聚合物网络的拓扑变化

• 批准号: 1006980
• 负责人: Arlette Baljon
• 金额: $ 26.4万
• 依托单位: San Diego State University Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-15 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1006980&HistoricalAwards=false
• 关键词: Topological; Changes; Associative; Polymer; Networks

TECHNICAL SUMMARYThis award supports theoretical and computational research and education on reversible polymer networks. These polymer networks show intriguing nonlinear behavior when subjected to shear or stress. For instance strong shear thinning has been observed when a uniform stress is applied to a model telechelic polymer. The system yields and forms two or more shear bands. In addition, it is found that rheochaotical fluctuations in the stress profile exhibit self-organized critical behavior. Under mechanical stress, slow aging, creep, dramatic failure, and rupture are observed, dependent on the stress level. After cessation of stress, the system slowly heals. These polymer systems consist of hydrophilic polymers with hydrophobic end-groups. In aqueous solution they form network structures since the hydrophobic ends self-assemble into micelles. It is believed that stress induces a novel microscopic network structure that might have spatial as well as temporal organization. Using a novel Molecular Dynamics/Monte Carlo hybrid model, the PI will study those microscopic topological changes and determine how they connect to the macroscopic nonlinear response. The topology of the network is characterized by the properties of its connectivity matrix, for example spectral density or degree distribution. In reversible networks micelles break apart and new ones form over time. The transition rates for these processes will be obtained from simulations and employed to construct a master equation that describes the network kinetics and can be used for further theoretical investigation. The results will be compared with experiments. The PI will also perform simulations and compare the simulation data to experiments on physically associating triblock copolymers that show rheological behavior very similar to that observed in biopolymer networks, for example a cross-linked actin network in a human cell or a cellulose network in a plant cell. In particular, all exhibit strain stiffening at relative low values of strain. Biological systems perform their function under applied mechanical stress. The PI will investigate the role of changes in network topology and dynamics. This project will provide valuable training opportunities for graduate and undergraduate students. It is integrated in an interdisciplinary educational program in math/physics and biology at San Diego State University. As part of this program the P.I. teaches a course on synthetic and biopolymers, in which results of her research group are discussed. San Diego State University enrolls a large number of minority students, many of whom take this course, participate in this program, or are part of the PI's research group. NONTECHNICAL SUMMARYThis award supports theoretical and computational research on long chain-like molecules, polymers, that can form junctions between their ends. The ends of the polymers prefer not to be in contact with water. In water, these molecules form network structures. Experiments show interesting behavior when these networks are subjected to mechanical stress. For instance, when slowly deformed the system suddenly yields. At higher deformations bands appear in which the molecules move at different speeds. After stopping the deformation, the system remembers it for a long time, but eventually slowly returns back to its original state. It is believed that stress induces a novel microscopic network structure. The PI will use simulation to study this behavior and to characterize the way the molecules are organized in the network. The research will advance understanding of experiments. The PI will also study polymers that behave similarly to networks of polymers that occur in living systems like the scaffolding in animal and plant cells. Biological systems perform their function under applied mechanical stress and the PI will investigate the role of changes in the way the polymers are organized in the network.Polymer networks in which bonds between molecules constantly break and recombine abound in nature. Examples are the cellulose network in plant cells and the fibril network in a human cell. The special mechanical properties of these polymer networks, for example their ability to relax back to their original structure and restructure after cessation of stress, enable these cells to perform their biological functions. These self-healing properties of transient networks are instrumental to the design of self-repairing smart nanomaterials and sensors.This project will provide valuable training opportunities for graduate and undergraduate students. It is integrated in an interdisciplinary educational program in math/physics and biology at San Diego State University. As part of this program the P.I. teaches a course on synthetic and biopolymers, in which results of her research group are discussed. San Diego State University enrolls a large number of minority students, many of whom take this course, participate in this program, or are part of the PI's research group.

该奖项支持可逆聚合物网络的理论和计算研究和教育。 这些聚合物网络显示出有趣的非线性行为时，受到剪切或应力。 例如，当向模型遥爪聚合物施加均匀应力时，已经观察到强剪切稀化。 系统产生并形成两个或多个剪切带。 此外，它被发现在应力分布的流变混沌波动表现出自组织的临界行为。 在机械应力下，观察到缓慢老化、蠕变、急剧失效和破裂，这取决于应力水平。 压力停止后，系统慢慢愈合。这些聚合物体系由具有疏水端基的亲水聚合物组成。 在水溶液中，它们形成网络结构，因为疏水末端自组装成胶束。 人们认为，压力诱导一种新的微观网络结构，可能具有空间和时间组织。 使用一种新的分子动力学/蒙特卡罗混合模型，PI将研究这些微观拓扑变化，并确定它们如何连接到宏观非线性响应。 网络的拓扑结构由其连接矩阵的性质来表征，例如谱密度或度分布。 在可逆网络中，随着时间的推移，胶束会分解并形成新的胶束。 这些过程的过渡率将从模拟中获得，并用于构建一个主方程，描述了网络动力学，并可用于进一步的理论研究。 将结果与实验进行比较。PI还将进行模拟，并将模拟数据与物理关联三嵌段共聚物的实验进行比较，这些实验显示出与生物聚合物网络中观察到的流变行为非常相似的流变行为，例如人类细胞中的交联肌动蛋白网络或植物细胞中的纤维素网络。特别是，所有表现出应变硬化在相对较低的应变值。 生物系统在施加的机械应力下执行其功能。 PI将研究网络拓扑和动态变化的作用。 该项目将为研究生和本科生提供宝贵的培训机会。 它被整合到圣地亚哥州立大学的数学/物理和生物学的跨学科教育计划中。作为该计划的一部分，P.I.教授一门关于合成和生物聚合物的课程，其中讨论了她的研究小组的结果。 圣地亚哥州立大学招收了大量的少数民族学生，他们中的许多人选修这门课程，参加这一项目，或者是PI研究小组的一员。非技术性总结该奖项支持长链状分子，聚合物，可以在其末端之间形成连接的理论和计算研究。 聚合物的末端优选不与水接触。在水中，这些分子形成网络结构。 实验表明，有趣的行为时，这些网络受到机械应力。 例如，当缓慢变形时，系统突然屈服。 在更高的变形下，出现了分子以不同速度运动的带。 在停止变形后，系统会记住它很长一段时间，但最终会慢慢恢复到原始状态。 据信，应力诱导了一种新的微观网络结构。 PI将使用模拟来研究这种行为，并表征分子在网络中的组织方式。 这项研究将促进对实验的理解。PI还将研究与生物系统中的聚合物网络类似的聚合物，如动物和植物细胞中的脚手架。生物系统在施加机械应力的情况下发挥功能，PI将研究聚合物在网络中组织方式的变化所起的作用。在自然界中，分子之间的键不断断裂和重组的聚合物网络比比皆是。例如植物细胞中的纤维素网络和人类细胞中的原纤维网络。这些聚合物网络的特殊机械性能，例如它们在压力停止后松弛回到其原始结构和重构的能力，使这些细胞能够执行其生物功能。瞬态网络的这些自修复特性有助于设计自修复智能纳米材料和传感器。本项目将为研究生和本科生提供宝贵的培训机会。 它被整合到圣地亚哥州立大学的数学/物理和生物学的跨学科教育计划中。作为该计划的一部分，P.I.教授一门关于合成和生物聚合物的课程，其中讨论了她的研究小组的结果。 圣地亚哥州立大学招收了大量的少数民族学生，他们中的许多人选修这门课程，参加这一项目，或者是PI研究小组的一员。