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

我们将研究高渗透聚合物体系的动力学和结构，以从分子到形态的角度来理解传输过程。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，可以定制高渗透性系统中的传输。裁剪程序将用于使材料不均匀，以通过包装不良、密度低和自由体积大的区域产生快速扩散。无序的高渗透性玻璃可以通过增加高自由体积区域的比例来产生，例如，通过具有笨重的，缓慢重新排列的骨干单元，这些骨干单元在玻璃形成时无法很好地包装。在共混物中，通过结合低玻璃化过渡聚合物和高玻璃化过渡聚合物来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，并表征该区域的较长长度尺度组织。核磁共振（NMR）波谱学将作为主要的实验方法，因为核磁共振是在分子结构的长度尺度上研究材料的工具。渗透剂的吸附位点将使用氙-129核磁共振进行检测，平移运动的短程方面将观察到氙-129光谱中位点之间的交换。利用自旋-晶格弛豫和固体状态线形状研究混合材料中高自由体积区域的局部节段运动。这些实验将研究纳米尺度上的特性，而更长的长度尺度，100纳米到微米尺度上的形态特性将通过脉冲场梯度（PFG）扩散实验进行研究。这种方法将被证明可以检测与纳米尺寸缺陷区域的较长距离组织或连通性相关的结构。我们将试图表明，这些区域导致高渗透率系统中的快速扩散，并在PFG实验中观察到高渗透率系统中弯曲和受限扩散的特征，其中表观扩散常数随着观察扩散的时间尺度的增加而减慢。计算机模拟将用于帮助理解这种行为，并澄清样品制备，样品历史和老化在高渗透聚合物中的作用。PFG核磁共振实验将用于提供与缺陷组织相关的长长度尺度上的老化和调理效应的独特观点。核磁共振将用于量化侧链晶体系统在结晶时的变化，当侧链将主链锁定为刚性的，尽管包装不良的状态。研究人员将通过与合作者网络的互动，将核磁共振实验结果与传统的渗透率和溶解度实验、力学实验、散射实验和介电实验的信息结合起来。这些聚合物系统具有重要意义，同时也是分离膜、控制输送系统和电池固体电解质的基础。膜分离系统是一种高效的分离永久性气体，如氮气和氧气的方式。分离膜可用于环境应用，在释放水和二氧化碳的同时收集有机气体。侧链结晶聚合物用作受控递送系统，该系统将允许高于侧链熔点的小分子通过，并且将包含高于熔点的小分子。所研究的两种混合物中的低玻璃化过渡成分是聚乙烯氧化物，它在电池应用中充当锂盐的溶剂。从拟议的研究中得到的理解将有助于改进此类应用。

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.