CAREER: Tailoring Free Volume in Nanocomposite Gas Separation Membranes

0846541N。LapeNSF化学和生物分离计划颁发的这一奖项支持哈维·马德学院的Nancy Lape教授通过定制无机/聚合物复合材料的自由体积，从而改善气体分离膜的工作。随着环境意识的提高和能源成本的上升，传统的气体分离方法，如吸收(用于CO2/CH4和CO2/N2分离)和低温蒸馏(用于N2/O2分离)正变得不那么有吸引力，而对无溶剂、高能效的膜分离过程的需求正在增加。不幸的是，膜过程完全依赖于高性能(足够高的渗透性和高选择性)膜材料的可用性，而这些材料目前还无法获得。最近对纳米复合膜的研究表明，在这一领域取得了可喜的进展：在超高自由体积聚合物中加入不透水的纳米颗粒，实际上可以提高相对于纯聚合物的渗透性，同时保持或增加其选择性。这与基于麦克斯韦模型的预测背道而驰，麦克斯韦模型长期被证明适用于微米级的颗粒，即渗透性随着不透水颗粒的添加而降低。这些改善已被证明是聚合物中自由体积增加的结果，但这种自由体积增加背后的机制，尽管通常归因于界面空洞的形成，但尚不清楚。此外，尚不清楚这种渗透增强如何依赖于颗粒大小、聚合物链刚性和其他界面效应。这项职业奖旨在通过对以下三个因素进行系统研究来解决这一不足：(1)初级颗粒和聚集体尺寸，(2)聚合物链刚性，以及(3)界面效应，采用四管齐下的方法：(A)复合膜形成。将使用各种材料和技术来制备复合膜，包括从纳米级到微米级的一系列颗粒尺寸，以研究Maxwell类型行为和渗透性增强之间的转变；一系列聚合物链刚性，包括橡胶、传统玻璃和超高自由体积玻璃聚合物；以及一系列颗粒表面处理，以检查界面效应。通过表面引发的原子转移自由基聚合(SI-ATRP)，可以消除界面空隙的形成，从而合成和检测在以前未研究过的膜中的渗透。(B)气体渗透试验。将对所有纯聚合物和复合膜进行渗透试验，以确定各种气体的渗透性和选择性。(C)表征。所有薄膜都将使用正电子湮没寿命谱(PALS)和密度测量来表征，以检查自由体积的大小和分布，并通过透射和扫描电子显微镜(TEM和SEM)来检查粒子的分散性。(D)分子模拟。我们将模拟纯聚合物和聚合物/无机纳米复合材料的分子水平构型、界面效应和理论自由体积，以阐明引起自由体积变化的分子水平结构的变化。虽然文献中充斥着纯聚合物的分子模拟(MM)结果，但纳米复合材料几乎是一个完全未经检验的领域。该项目的主要教育目标集中在两个方面：课程和教育方法开发以及综合本科生研究和多层次指导计划。为了解决第一个方面，将开发和传播以挑战为基础的教学模块，以便在课程中使用。此外，还计划为哈维马德学院(HMC)聚合物化学和工程专业的本科生开设一门新课程。新课程将包括拟议研究领域的实验模块。这项研究将完全由本科生和高中研究人员进行。本科生将从一个多层次的结构化指导计划中受益，在该计划中，他们由PI、校友和彼此指导，并将接受高中生导师的培训。为本科生和高中生的研究和辅导开发的技术成果和模型将通过出版物和演示文稿广泛传播。

0846541N. LapeThis NSF award by the Chemical and Biological Separations program supports work by Professor Nancy Lape at Harvey Mudd College to improve gas separation membranes by tailoring free volume, and therefore gas separation properties, of inorganic/polymer composites. With increasing environmental awareness and rising energy costs, traditional gas separation methods such as absorption (for CO2/CH4 and CO2/N2 separations) and cryogenic distillation (for N2/O2 separations) are becoming less attractive, while demand is increasing for solvent-free, energy-efficient membrane separation processes. Unfortunately, membrane processes are entirely dependent on the availability of high-performance (sufficiently high permeability and high selectivity) membrane materials that are not currently available. Recent research in nanocomposite films has shown promising gains in this area: the addition of impermeable nanoparticles to an ultra-high free volume polymer can actually increase permeability relative to the pure polymer while maintaining or increasing its selectivity. This runs counter to predictions based on the Maxwell model, long proven for micron-size particles, of permeability decreases upon the addition of impermeable particles. The improvements have been shown to be the result of free volume increases in the polymer, but the mechanism behind this free volume increase, while typically attributed to the formation of interfacial voids, is not understood. Additionally, it is unknown how this permeation enhancement depends on particle size, polymer chain rigidity, and other interfacial effects.This CAREER award aims to address this deficiency by performing a systematic investigation of the following three factors: (1) primary particle and aggregate size, (2) polymer chain rigidity, and (3) interfacial effects using a four-pronged approach: (a) Composite membrane formation. A variety of materials and techniques will be used to prepare composite films including a range of particle sizes from nanoscale to microscale to examine the transition between Maxwell-type behavior and permeability enhancement; a range of polymer chain rigidity including rubbery, conventional glassy, and ultra-high free volume glassy polymers; and a range of particle surface treatments to examine interfacial effects. Permeation in previously unstudied membranes will be synthesized and examined using surface-initiated atom-transfer radical polymerization (SI-ATRP) which eliminates interfacial void formation.(b)Gas permeation tests. Permeation tests on all pure polymer and composite films will be run to determine the permeability and selectivity of various gases.(c) Characterization. All films will be characterized using positron annihilation lifetime spectroscopy (PALS) and density measurements to examine free volume size and distribution and transmission and scanning electron microscopy (TEM and SEM) to examine particle dispersion.(d) Molecular Modeling. The molecular-level configuration, interfacial effects, and theoretical free volume of pure polymers and polymer/inorganic nanocomposites will be modeled to illuminate the changes in molecular-level architecture that give rise to changes in free volume. While the literature abounds with molecular modeling (MM) results for pure polymers, nanocomposites are an almost entirely unexamined area for MM.The main educational goals of this project are centered on two aspects: Course and Educational Method Developments and an Integrated Undergraduate Research and Multi-Tiered Mentoring Program. To address the first aspect, Challenge-Based Instruction Modules will be developed and disseminated for use in courses. Also a new course aimed at chemistry and engineering Harvey Mudd College (HMC) undergraduates in Polymer Chemistry and Engineering is planned. The new course will include experimental modules in the area of the proposed research. The research will be carried out entirely by undergraduate and high school researchers. The undergraduates will benefit from a multi-tiered structured mentoring program in which they are mentored by the PI, alumni, and each other, and will be trained as mentors for high school students. Technical results and the models developed for undergraduate and high school student research and mentoring will be widely disseminated via publications and presentations.