Role of Chain Architecture on the Properties of Linear and Star Chain Thin Film Polymer Systems

技术概述：虽然在过去十年中，在纳米尺度上理解和控制聚合物的结构和性质方面取得了重大进展，但科学和技术方面的重大挑战和机遇仍然存在。研究主要集中在线性链聚合物体系的性质上；聚合物链结构对薄膜性能的影响在很大程度上仍未被探索。本研究的目的是了解链结构对薄膜线性/星形分子和星形/星形分子混合物的混相、动力学、玻璃化转变和老化现象的影响。研究星形聚合物有几个原因。在界面吸附时，星型分子的熵损失比线性链小。除了它们的界面性质外，星形分子的动力学，特别是最长弛豫时间，？ä，粘度，？Ø，慢；？ä和？Ø与链臂长度的聚合度N成指数比例。也许星形分子最吸引人的地方是，对于低功能f和足够大的N，它们表现出与线性链相似的性质。然而，对于非常大的f，它们表现出类似于胶体的行为。在理论预测的指导下，利用中子、电子、x射线、介电光谱、椭偏仪和机械仪器等工具，设计了一个实验项目，以了解约束和界面相互作用对星形分子体系（线性/星形分子和星形分子/星形分子混合物）的混溶性、微观结构、结构不稳定性、老化现象和动力学的影响。这些系统的特性承诺是真正迷人的，并为新科学和应用提供了有趣的可能性。非技术概述：从涂层到有机电子器件和传感器的功能材料，各种技术都依赖于聚合物薄膜的特性和性能。聚合物薄膜的研究主要集中在线性链聚合物上；人们对不同结构的链的性质知之甚少，比如星形聚合物。星形分子，由于它们的结构提供了许多潜在的，独特的，在某些应用中优于线性链系统的优势。例如，它们显示出粘合剂应用的前景，并有可能用于某些电池和传感器应用，因为它可以利用多臂结构来附着不同功能的分子/纳米颗粒。本提案的目标是发展链结构对线性链/星形分子和星形/星形分子混合物的性质（混相、老化现象、玻璃化转变和动力学）的作用的理解。这是一个跨学科的项目，涉及聚合物物理，化学，界面科学，热力学和传输过程。它将包括一个种族多元化的群体，包括代表性不足的少数民族，本科生、博士生和高中生。该计划还包括材料合成领域的国际合作者。首席研究员的外展活动包括在技术会议上的公开演讲，退休小组和参加各种国家研究理事会的研究和董事会以及技术协会委员会。

TECHNICAL SUMMARY: While during the last decade significant progress has been made toward understanding and controlling the structure and properties of polymers at the nanoscale, major challenges and opportunities, both scientific and technological, remain. Research has largely been devoted to the properties of linear-chain polymer systems; the influence of polymer chain architecture on the properties of thin films has largely remained unexplored. The goal of this proposal is to understand the effect of chain architecture on the miscibility, dynamics, glass transition and aging phenomena in thin film linear/star molecule and star/star molecule mixtures. There are several reasons for studying star polymers. Star molecules suffer a smaller loss in entropy than linear chains upon adsorption at interfaces. In additional to their interfacial properties, the dynamics of star shaped molecules, specifically the longest relaxation time, ?ä, and the viscosity, ?Ø, are slow; ?ä and ?Ø scale exponentially with the degree of polymerization, N, of the chain arm length. Perhaps the most fascinating aspect of star shaped molecules is that for low functionalities, f, and for sufficiently large N, they exhibit properties similar to linear chains. However, for very large f, they exhibit behavior akin to colloids. Guided by theoretical predictions, an experimental program, which exploits tools that include neutrons, electrons, X-rays, dielectric spectroscopy, ellipsometry and mechanical instruments, has been designed to develop an understanding of the influence of confinement and interfacial interactions on miscibility, microstructure, structural instabilities, aging phenomena and dynamics in star shaped molecule based systems (linear/star molecule and star/star molecule mixtures). The properties of these systems promise to be truly fascinating and present intriguing possibilities for new science and applications.NON-TECHNICAL SUMMARY: Diverse technologies, from coatings to functional materials for organic electronic devices and sensors, rely on the properties and performance of polymer thin films. Research on thin polymer films has primarily been devoted to linear chain polymers; little is understood about the properties of chains of different architectures, such as star shaped polymers. Star shaped molecules, by virtue of their architecture offer a number of potential, and unique, advantages over linear chain systems for certain applications. For example, they show promise for adhesive applications, and potentially for certain battery and sensor applications, as it is possible to take advantage of the multi-arm architecture for attachment of molecules/nanoparticles of varying functionalities. The goal of this proposal is to develop an understanding of the role of chain architecture on properties (miscibility, aging phenomena, glass transition and dynamics) of linear chain/star shaped molecule and of star/star molecule mixtures. This is an interdisciplinary program, involving polymer physics, chemistry, interfacial science, thermodynamics and transport processes. It will include an ethnically diverse group, including under represented minorities, of undergraduates, PhD students and high school students. The program also includes an international collaborator in the area of materials synthesis. Outreach activities of the principal investigator include public lectures at technical meetings, retired groups and participation on various National Research Council studies and boards and technical society committees.