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.

克里夫·亨德森（Cliff Henderson） /佐治亚州立大学。技术的这项工作的总体目标是进一步表征聚合物超薄膜和聚合物在受约束几何形状中的扩散行为，阐明了这种行为的长度尺度和大小，并发展了对观察现象负责的机制的自我一致和全面的基本理解。 PIS来自实验和分子模拟的初步结果表明了一个基于聚合物链迁移率和自由体积分布的变化的新型模型，可以解释所有观察到的玻璃转变，热膨胀系数，扩散和质子电导率的效果，以一致的方式导致。 这两种协同的机制结合在一起，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。 已经组装了一个独特的团队，以将实验表征与分子模拟整合在一起，以阐明这些薄膜现象的起源。 克利福德·亨德森（Clifford Henderson）教授指导实验研究，并在聚合物表征和聚合物薄膜方面具有丰富的经验。 彼得·卢多维斯（Peter Ludovice）教授在分子模拟方面拥有广泛的专业知识，并监督建模工作。该提案的智力优点可以广泛地定义为：（1）表征超薄聚合物膜的扩散行为，（2）开发一个基本模型来解释聚合物超薄膜和聚合物的生理化学特性。这项活动的更广泛影响包括：（1）为克服微观石刻中的某些路障提供指导和机会，以使微电学行业受益，（2）提供有关方法的指导，以增强燃料电池和气体分离的聚合物膜性能，并以较小的培训和较小的学生进行较小的学生，并在较小的学生中进行研究，并（4）进行研究，并（3）型和研究的学生（4）模型（4），并（3） background：目前在从根本上了解聚合物薄膜和聚合物的热力学和传输特性（例如，复合膜）（例如复合膜）以及这些特性对聚合物类型，界面类型，膜厚度和制备条件的依赖性。 在各种应用中，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，薄膜和狭窄的几何形状结构中的聚合物是关键要素。 对聚合物薄膜的生理化学特性缺乏基本理解，这是对这些应用改进的材料和过程的合理设计的障碍。最近的聚合物膜研究表明，随着膜的厚度降低到一些临界厚度以下，各种聚合物特性偏离了散装行为，这取决于感兴趣的特性。 到目前为止，尚无提出的单一理论可以充分解释所有观察到的薄膜行为，在许多情况下，观察到的膜特性变化似乎相互不一致。 例如，已经观察到，当膜在弱相互作用的底物上覆盖时，受支持的聚合物薄膜的玻璃过渡温度（TG）可能会减少，并且目前的解释是基于膜表面附近聚合物链迁移率的增加。 另一方面，PI的最新实验表明，这种受支持的薄膜中小渗透分子的扩散系数随着膜厚度降低而大大减少。 简单的链移动性论点无法解释这一点，实际上将预测相反的行为。 PIS的最新测量还表明，随着膜厚度降低，超薄聚合物膜的质子电导率不会显示出类似于气态渗透行为的减少。