Interplay of Segmental and Global Dynamics in Cross-Linking Networks

本研究对一类重要的复杂体系，即化学交联聚合物网络进行了系统的研究。这些系统的动力学信息将通过宽带介质弛豫光谱和动态力学光谱实验产生，并将根据适当的模型进行验证。所提出的研究为早期聚合物网络动力学研究增加了一个重要的新维度，因为所选择的系统为早期聚合物网络动力学研究提供了研究维度，因为所选择的系统除了表现出横向偶极矩分量外，还表现出沿链轮廓持续累积的偶极矩，该偶极矩可以通过正常模式过程放松。当重复单元缺乏垂直于链轮廓的对称平面时，聚合物分子的这部分偶极矩就出现了。对于n个这样的单元序列，偶极子向量必须与位移向量相关，因此，从正常过程的研究中，人们不仅可以确定弛豫时间，还可以确定端到端距离的均方。因此，选择用于研究的网络形成材料将具有独特的特征，即它们的分子结构将有助于检测从局部到片段到全局的整个分子运动层次。可以预期，结构和地形的可控变化将导致具有所需特征的定制网络的能力，其响应可以通过在比每个动态过程的特征时间更短或更长的时间尺度上的选择性接触而改变。最终，将有可能通过分子概念来实现网络的宏观性质。拟议的研究将具有比上述目标更广泛的影响。这是因为各种长度尺度的动力学相互作用对许多其他复杂系统的行为至关重要，例如自组装和各种纳米结构，以及从基因治疗、蛋白质动力学和蛋白质折叠到影响DNA局部和全局动力学的环和十字形的生物相关问题的宿主。通过本科生和研究生的讲座和实验课程，实现科研与教学的结合。拟议的工作还将通过在理工学院的YES（青年工程与科学）暑期项目的支持下，容纳来自纽约市高中的一些未被充分代表的少数民族学生，从而有助于增强种族多样性。

This research is for a systematic study on one important type of complex systems, namely chemically cross-linked polymer networks. Information about the dynamics of these systems will be generated experimentally by broad-band dielectric relaxation spectroscopy and dynamic mechanical spectroscopy, and will be verified against the appropriate models. The proposed research adds a major new dimension to the earlier studies of dynamics in polymer networks in that the systems selected for study dimension to the earlier studies of dynamics in polymer networks in that the systems selected for study exhibit, in addition to the transverse dipole moment component, a persistent cumulative dipole moment along the chain contour that can be relaxed via the normal mode process. This part of the dipole moment of the polymer molecules is present when the repeat unit lacks a plane of symmetry perpendicular to the chain contour. For a sequence of n such units, the dipole vector must correlate with the displacement vector and thence from the studies of the normal processes one can determine not only the relaxation time but also the mean square end-to-end distance. Therefore, the network-forming materials chosen for study will have a unique characteristic in that their molecular architecture will be conducive to the detection of the entire hierarchy of molecular motions, ranging from local to segmental to global. It is anticipated that the controlled variation in the structure and topography will result in the ability to tailor-make networks with desired characteristics whose response can be varied by a selective engagement on the time scales shorter or longer than the characteristic time of each dynamic process. Ultimately, it will be possible to realize the macroscopic properties of the networks by molecular concepts.%%5The proposed research will have implications broader than the aforementioned goals. This is so because the interplay of dynamics of various length scales is crucial to the behavior of many other complex systems, such as self-assemblies and various nanostructures, as well as to the host of bio-related issues that range from gene therapy, protein dynamics and protein folding to the loops and cruciforms that affect the local and global dynamics of DNA's. The integration of research and education will be realized through lectures and laboratory courses for undergraduate and graduate students. The proposed work will also contribute to the enhancement of ethnic diversity by accommodating a number of under-represented minority students from New York City high schools under the aegis of the YES (Youth in Engineering and Science) summer program at Polytechnic.