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

琼斯教授和英格菲尔德将研究高渗透性聚合物，包括取代聚乙炔和无定形特氟龙(杜邦商标)。他们用来理解渗透率和吸附数据的典型解释方法是双模式模型和自由体积理论。为了获得更多的分子观点，核磁共振波谱将是他们研究的主要技术。核磁共振既可以作为渗透剂，也可以作为基质。具体地说，将使用自旋-晶格弛豫时间以及一维和二维(2D)线形实验来表征渗透剂或聚合物主干的重定向运动。克拉克的琼斯和英格菲尔德也在这个实验中使用了氢、碳-13和氙气-129。在分子水平上，分子间偶极-偶极-自旋-晶格驰豫可以提供平移信息，一维和二维氙气-129线形实验也可以提供信息。将进行两个层次的结构试验。第一类是质子自旋扩散实验，用于测量包含渗透剂分子的区域的区域大小，以及对孔大小和团簇大小敏感的Xe-129化学位移测量。第二组结构实验是关于局域分子间结构的，如2D零量子自旋交换、REDOR和戏剧。这些短程结构实验可能对高选择性材料特别感兴趣。局部长度尺度上的信息将与PFG核磁共振或经典渗透率的长程迁移率测量相结合。聚合物本身的状态是相关的。例如，高浓度的预制物会降低基质的玻璃化转变，从而损害膜的机械性能。在共混物中，渗透剂选择性地溶胀结构域可以改变基质迁移率随浓度的变化。基于混合物、气凝胶和聚合物/气凝胶复合材料的系统将采用相同的实验策略进行研究。一些人认为高自由体积、高渗透聚合物的行为更像二氧化硅气凝胶，因此可以使用渗透剂分子水平迁移率的直接比较来检验这一观点。在共混体系中，聚合物组分链段运动的动态耦合程度可以与通过共混的平移扩散的性质进行比较。共混物中浓度非均质性的区域大小预计会影响到预想的迁移率和聚合物链之间的动态耦合程度。琼斯教授和英格菲尔德教授将在分子水平上进一步了解气体和其他小分子在用作分离膜和阻隔膜的材料中的结构和运动。合成膜用于分离气体和液体的工业用途已经很多，但还在继续开发新材料，旨在通过更高的渗透速率和更好的选择性来提高效率。传统聚合物目前被用作许多合成膜的基础，但这是一种新的经典技术，涉及对更传统聚合物采用的标准描述的扩展。

9901416JonesProfessor Jones and Inglefield will study high permeability polymers including substituted polyacetylenes and Amorphous Teflon (DuPont Trademark). Typical interpretational approaches which will be used by them to understand permeability and sorption data are the dual mode model and free volume theory. To obtain a more molecular view, Nuclear Magnetic Resonance Spectroscopy ( NMR) will be the primary technique employed in their study. NMR is capable of both the penetrant and the host matrix. Specifically spin-lattice relaxation times and one and two-dimensional (2D) line shape experiments will be used to characterize reorientational motion of either the penetrants or the polymer backbone. Deuterium and carbon-13 and xenon-129 have also been employed in this experiment by Jones and Inglefield at Clark. At a molecular level, intermolecular dipole-dipole spin-lattice relaxation can provide information on translation as can one and two dimensional xenon-129 line shape experiments. Two levels of structural experiments will be performed. The first class is proton spin-diffusion experiments to measure domain size of the regions containing penetrant molecules and also xenon-129 chemical shift measurements which are sensitive to pore size and cluster size. The second set of structural experiments is for local intermolecular structure such as 2D zero quantum spin exchange, REDOR and DRAMA. These short range structure experiments may be especially interesting in high selectivity materials. The information on local length scales will be meshed with long range measurements of mobility by PFG NMR or classical permeability. The state of the polymer itself is relevant. For instance, high concentrations of permeant can lower the glass transition of the matrix impairing the mechanical properties of the membrane. In blends, selective swelling of domains by the penetrant can alter that changes of the matrix mobility with concentration can be established. Systems based on blends, aerogels and polymer/aerogel composites will be studied with the same experimental strategy. Some consider high free volume, high permeability polymers to behave more like silica aerogels so a direct comparison of molecular level mobility of permeants can be used to test this view. In blend systems, the extent of dynamic coupling of the segmental motion of the polymer components can be compared with the nature of translational diffusion through the blend. Domain size of concentration heterogeneities in the blend is expected to affect both permeant mobility and the level of dynamic coupling between polymer chains. Barrier and highly selective materials will be studied as comparisons to the high permeability materials.Professors Jones and Inglefield will further the molecular level understanding of structure and motion of gases and other small molecules in materials used as separation membranes and barrier films. Industrial use of synthetic membranes to separate gases and liquids is already significant but there is continued development of new materials designed to improve efficiency through higher permeation rates and better selectivity. Conventional polymers are currently used as the basis of many synthetic membranes but a new classical techniques involving extensions of standard descriptions employed for the more conventional polymers.