NMR Studies of Dynamics and Structure of Penetrants and Polymers in High Permeability Membrane Materials and Barrier Materials

将研究高渗透聚合物体系的动力学和结构，以发展对运输的分子到形态层面的理解。在高渗透系统中的传输将通过使用重复单元的结构修改、混合、结晶、样品制备和样品历史来定制。裁剪程序将被用来使材料不均匀，以在包装不良、密度低和自由体积高的区域产生快速扩散。无序的高渗透玻璃将通过增加高自由体积区域的比例来生产，例如，通过具有笨重的、缓慢地重新排列的主干单元来生产，这些主干单元在玻璃形成时不能很好地包装。在共混物中，通过将低玻璃化转变聚合物与高玻璃化转变聚合物相结合，将产生高自由体积区域。将确定缺陷或高自由体积区域的分子水平特征，并将表征区域的较长尺度组织。核磁共振波谱将被用作主要的实验方法，因为核磁共振已被公认为在分子结构的长度尺度上研究材料的工具。渗透剂的吸附位置将用氙气-129核磁共振进行检查，平移运动的短程方面将作为氙气-129光谱中位置之间的交换来观察。我们将利用自旋晶格驰豫和固态线形状来研究共混物中高自由体积区域的局部分段运动。这些实验将考察纳米尺度上的特性，而更长的尺度，即100‘S纳米到微米尺度上的形态特性将通过脉冲场梯度扩散实验来研究。该方法将被展示为检测与纳米尺寸缺陷区域的较长范围的组织或连通性相关的结构。我们将试图证明，在高渗透系统中，这些区域导致快速扩散，并在高渗透系统中观察到曲折和受限扩散的特征，其中，在PFG实验中，表观扩散常数随着观察到扩散的时间尺度的增加而减缓。计算机模拟将被用来帮助理解这种行为，并阐明样品制备、样品历史和老化在高渗透聚合物中的作用。PFG核磁共振实验将被用来提供与缺陷组织相关的长长度尺度上的老化和条件化效应的独特视角。当侧链将主链锁定为刚性但填充不良的状态时，将使用核磁共振来量化侧链结晶体系在结晶时的变化。研究人员将通过与合作者网络的互动，将核磁共振实验的结果与传统的渗透性和溶解性实验、机械实验、散射实验和介电实验的信息结合起来。这些聚合物体系是基本感兴趣的，但也是电池中分离膜、受控输送系统和固体电解液的基础。膜分离系统是分离氮气和氧气等永久性气体的一种能源效率高的形式。分离膜可用于环境应用，以收集有机气体，同时释放水和二氧化碳。侧链结晶聚合物被用作受控输送系统，它将允许小分子通过侧链熔点以上，并将包含熔点以上的小分子。其中两种混合物的低玻璃化转变组分是聚氧乙烷，它在电池应用中充当锂盐的溶剂。从拟议的研究中形成的理解将有助于改进这类应用。

The dynamics and structure of high permeability polymeric systems will be studied to develop a molecular to morphological level of understanding of transport. Transport in high permeability systems will be tailored through the use of structural modification of repeat units, blending, crystallization, sample preparation and sample history. The tailoring procedures will be used to make the materials inhomogeneous to produce rapid diffusion through regions of poor packing, low density, and high free volume. Disordered high permeability glasses will be produced by increasing the fraction of high free volume regions by for instance having bulky, slowly rearranging backbone units that are unable to pack well as the glass is formed. In blends, high free volume regions will be produced by combining a low glass transition polymer with a high glass transition polymer. The molecular level characteristics of the defect or high free volume regions will be determined and the longer length scale organization of the regions will be characterized. Nuclear magnetic resonance (NMR) spectroscopy will be used as the primary experimental method since NMR is well established as a tool for the study of materials on the length scale of molecular structure. Sorption sites of penetrants will be examined using xenon-129 NMR and the short range aspects of translational motion will be observed as exchange between sites in xenon-129 spectra. Local segmental motion in high free volume regions in a blend will be studied using spin-lattice relaxation and solid state line shapes. These experiments will look at properties on the nanometer scale while longer length scale, morphological properties on a scale of 100's nanometers to microns will be studied by pulse field gradient (PFG) diffusion experiments. This method will be shown to detect structure associated with the longer range organization or connectivity of the nanometer sized defect regions. We will attempt to show that these regions lead to rapid diffusion in high permeability systems and to the observation of the signature of tortuous and restricted diffusion in high permeability systems where the apparent diffusion constant slows as the time scale over which diffusion is observed increases in the PFG experiment. Computer simulation will be used to aid in understanding such behavior and to clarify the role of sample preparation, sample history and aging in high permeability polymers. PFG NMR experiments will be used to provide a unique view of aging and conditioning effects on the long length scale associated with the organization of defects. NMR will be used to quantify the changes in side chain crystalline systems upon crystallization when the side chains lock the backbone into a rigid though poorly packed state. The investigators will combine the results of the NMR experiments with information from traditional permeability and solubility experiments, mechanical experiments, scattering experiments and dielectric experiments through interaction with a network of collaborators.These polymer systems are of fundamental interest but also serve as the basis for separation membranes, controlled delivery systems and solid electrolytes in batteries. Membrane separation systems are an energy efficient form of separation of permanent gases such as nitrogen and oxygen. Separation membranes can be used in environmental applications to collect organic gases while releasing water and carbon dioxide. The side chain crystalline polymers are used as controlled delivery systems which will allow the passage of small molecules above the melting point of the side chain and will contain the small molecules above the melting point. The low glass transition component in two of the blends to be studied is polyethylene oxide which acts as a solvent for lithium salts in battery applications. The understanding developed from the proposed research will aid in improving such applications.