Characterization and Understanding of the Anomolous Diffusion Behavior in Polymer Ultra-thin Films

聚合物超薄膜中反常扩散行为的表征和理解

• 批准号: 0652032
• 负责人: Clifford Henderson
• 金额: --
• 依托单位: Georgia Tech Research Corporation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-06-01 至 2010-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0652032&HistoricalAwards=false
• 关键词: Characterization; Understanding; Anomolous; Diffusion; Behavior

Cliff Henderson / Georgia Inst. TechnologyThe overarching goals of this work are to further characterize the diffusion behavior of polymer ultra-thin films and polymers in confined geometries, elucidate the length scales and magnitudes of such behavior, and to develop a self consistent and comprehensive fundamental understanding of the mechanisms that are responsible for the observed phenomena. Preliminary results by the PIs from both experiment and molecular simulation suggest a novel model based on changes in both polymer chain mobility and free volume distribution that can explain all of the observed glass transition, coefficient of thermal expansion, diffusion, and proton conductivity results in a consistent manner. Combined, these two concerted mechanisms can lead to the rich diversity of polymer thin film behavior observed thus far. A unique team has been assembled to integrate experimental characterization with molecular simulation in order to elucidate the origin of these thin film phenomena. Professor Clifford Henderson directs the experimental studies and has extensive experience in polymer characterization and polymer thin films. Professor Peter Ludovice has extensive expertise in molecular simulation and l supervises the modeling work. The intellectual merits of the proposal can broadly be defined as: (1) characterizing the diffusion behavior of ultra-thin polymer films and (2) developing a fundamental model to explain the physiochemical properties of polymer ultra-thin films and polymers in confined geometries. The broader impacts of this activity include: (1) providing guidance on and opportunities for overcoming some of the roadblocks in microlithography to benefit the microelectronics industry, (2) providing guidance on methods to enhance polymer membrane performance for fuel cells and gas separations, (3) educating undergraduate and graduate students in a manner that synergistically blends modeling and experiment, and (4) enhancing minority and secondary school education in science and engineering.Background: Currently there are significant knowledge gaps in fundamentally understanding the thermodynamic and transport properties of polymer thin films and polymers in confined systems (e.g. composite membranes), and the dependence of these properties on polymer type, interface type, film thickness, and preparation conditions. Polymers in thin film and confined geometry configurations are a critical element today in a variety of applications including semiconductor manufacturing, biomedical and tissue engineering, industrial gas separations, and fuel cells. The lack of a fundamental understanding of the physiochemical properties of polymer thin films poses a roadblock to the rational design of improved materials and processes for these applications. Recent polymer film studies have shown that a wide variety of polymer properties deviate from bulk behavior as the film thickness decreases below some critical thickness that varies depending on the property of interest. No single theory proposed thus far can adequately explain all of the observed thin film behavior, and in many cases the observed changes in film properties appear to be inconsistent with one another. For example, it has been observed that the glass transition temperature (Tg) of supported polymer thin films can decrease when the film is coated on a weakly interacting substrate and current explanations of this are based on increases in polymer chain mobility near the film surfaces. On the other hand, recent experiments by the PIs have shown that the diffusion coefficient of small penetrant molecules in such supported thin films decreases dramatically as the film thickness decreases. The simple chain mobility argument does not explain this and would in fact predict an opposite behavior. Recent measurements by the PIs also suggest that the proton conductivity of ultra-thin polymer films does not exhibit reductions similar to the gaseous penetrant behavior as film thickness decreases.

Cliff亨德森/格鲁吉亚Inst. TechnologyThe总体目标这项工作是进一步表征聚合物超薄膜和聚合物在受限几何形状中的扩散行为，阐明这种行为的长度尺度和幅度，并对所观察到的现象负责的机制发展自洽和全面的基本理解。 PI从实验和分子模拟的初步结果表明，一种新的模型的基础上的变化，聚合物链的流动性和自由体积分布，可以解释所有观察到的玻璃化转变，热膨胀系数，扩散和质子传导率的结果在一个一致的方式。 结合起来，这两个协同机制可以导致迄今为止观察到的聚合物薄膜行为的丰富多样性。 一个独特的团队已经组装到整合实验表征与分子模拟，以阐明这些薄膜现象的起源。 Clifford亨德森教授指导实验研究，并在聚合物表征和聚合物薄膜方面拥有丰富的经验。 Peter Ludovice教授在分子模拟方面拥有丰富的专业知识，我负责监督建模工作。该方案的智力价值可以概括为：（1）表征超薄聚合物膜的扩散行为和（2）开发一个基本模型来解释聚合物超薄膜和聚合物在受限几何形状中的物理化学性质。这项活动的广泛影响包括：（1）为克服微光刻中的一些障碍提供指导和机会，以使微电子工业受益，（2）为提高用于燃料电池和气体分离的聚合物膜性能的方法提供指导，（3）以协同混合建模和实验的方式教育本科生和研究生，（4）加强少数民族和中等学校的科学和工程教育。目前，在从根本上理解聚合物薄膜和聚合物在受限系统中的热力学和输运性质方面存在重大的知识缺口（例如复合膜），以及这些性质对聚合物类型、界面类型、膜厚度和制备条件的依赖性。 薄膜和受限几何构型的聚合物如今在包括半导体制造、生物医学和组织工程、工业气体分离和燃料电池在内的各种应用中是关键要素。 缺乏对聚合物薄膜的物理化学性质的基本理解，对这些应用的改进材料和工艺的合理设计构成了障碍。最近的聚合物膜研究已经表明，随着膜厚度降低到低于取决于感兴趣的性质而变化的某一临界厚度，各种各样的聚合物性质偏离本体行为。 到目前为止，还没有一个单一的理论可以充分解释所有观察到的薄膜行为，在许多情况下，观察到的薄膜性质的变化似乎是相互不一致的。 例如，已经观察到，当膜涂覆在弱相互作用的基底上时，支撑的聚合物薄膜的玻璃化转变温度（Tg）可以降低，并且目前对此的解释是基于膜表面附近的聚合物链迁移率的增加。 另一方面，PI最近的实验表明，在这种支撑薄膜中的小渗透剂分子的扩散系数随着膜厚度的减小而显著降低。 简单的链式流动性论证并不能解释这一点，事实上，它会预测一种相反的行为。 PI最近的测量结果也表明，超薄聚合物膜的质子传导率并没有表现出类似的气体渗透剂的行为减少膜厚度减小。