CAREER: Fundamentals of the Relationship between Pore Structure and Transport of Light Gases in Materials with a Hierarchy of Pore Sizes

这项由化学和生物分离计划颁发的NSF奖支持佛罗里达大学的Sergey Vasenkov教授的工作，他的工作是获得具有孔大小等级的材料的结构属性与这些材料中气体在不同长度的分子位移尺度上的传输属性之间的关系的基本知识。用于气体混合物分离的多孔膜通常在结构上是非均质的。特别是，混合基质膜包含不同大小的相互连接的孔网络，即孔径接近气体分子大小的微孔网络和大得多的中孔网络。这种膜在有效分离二氧化碳、甲烷和氮气等小分子气体方面具有巨大的潜力。在过去的十年中，在理解具有相同或相似孔径的孔隙网络中的气体传输方面取得了重大进展。同时，含有不同大小的孔道网络的材料中的扩散仍然知之甚少。该项目的研究目标是量化具有孔网络层次的材料中小(即微米和亚微米)长度尺度上的不同类型的气体传输，并找到这种传输与宏观远程扩散之间的关系。拟议的研究重点是测量山梨醇沿和通过微孔颗粒与其周围环境之间的界面的扩散。此外，还将研究山梨醇分子在小尺度上的相关运动对长距离扩散的影响。假设这些类型的传输可以对气体在分层多孔材料中的远程扩散做出显著和可量化的贡献。气体传输的测量将使用一种独特的实验方法：脉冲场梯度(PFG)核磁共振在高场(17.6T)和高梯度(高达36T/m)下进行。实验研究将得到动态蒙特卡罗模拟的补充。在该项目教育计划的框架内，将引入一个新的面向少数民族本科生的系级计划。该计划包括组织辅导研讨会，提供研究经验，并将新生少数民族学生与PI和系其他教职员工小组中获得研究经验的学生配对。高场高梯度PFG核磁共振硬件和测量方法将作为一种新的多用户资源在国家磁体实验室开发。国际核磁共振学会为实现这一目标的计划包括：(I)培训他的学生就PFG核磁共振测量程序向其他用户提供建议，以及(Ii)开发一份此类测量手册。外展活动包括为高中教师和学生扩大当地研讨会(JSEHS)，并在夏季接待皮？S小组的10年级和11年级学生。拟议的研究将量化不同类型的小长度尺度上的气体传输，并建立这些类型的传输与多孔膜和相关材料中的宏观远程扩散之间的定量关系。通过宏观多孔系统的分子通量由长程扩散系数决定。因此，在拟议的研究中产生的新知识将使设计具体的策略来优化多孔膜中的气体通量，同时保持分离选择性。

This NSF award by the Chemical and Biological Separations program supports work by Professor Sergey Vasenkov at University of Florida to obtain fundamental knowledge of the relationship between structural properties of materials with a hierarchy of pore sizes and transport properties of gases in these materials on different length scales of molecular displacements. Porous membranes fabricated for separations of gas mixtures are usually structurally heterogeneous. In particular, mixed matrix membranes contain interconnected networks of pores of different sizes, i.e. networks of micropores with pore sizes approaching the sizes of gas molecules and networks of much larger mesopores. Such membranes have great potential for effective separations of small gas molecules such as CO2, CH4, and N2. Over the last decade significant progress has been made in understanding gas transport in pore networks with uniform or similar pore sizes. At the same time, diffusion in materials containing a hierarchy of pore networks with very different pore sizes is still poorly understood. The research goal of the project is to quantify different types of gas transport on small (i.e. micrometer and submicrometer) length scales in materials with a hierarchy of pore networks and to find a relationship between such transport and macroscopic long range diffusion. The proposed studies focus on measurements of sorbate diffusion along and through the interfaces between microporous particles and their surroundings. In addition, the effect of correlated motions of sorbate molecules on small length scales on the long range diffusion will be investigated. The hypothesis is that these types of transport can make a significant and quantifiable contribution to long range diffusion of gases in hierarchical porous materials. Measurements of gas transport will be carried out using a unique experimental approach: pulsed field gradient (PFG) NMR at high field (17.6 T) and high gradients (up to 36 T/m). Experimental studies will be complemented by dynamic Monte Carlo simulations.In the framework of the education plan of the project a new departmental program for minority undergraduate students will be introduced. The program includes organizing mentoring seminars, providing research experiences, and pairing freshmen minority students with the students who obtained research experience in the groups of the PI and other faculty members of the department. High field and high gradient PFG NMR hardware and measurement methodology will be developed as a new multi-user resource at the National Magnet Lab. The PI's plans to reach this goal include: (i) training his students to advise other users on the procedures of PFG NMR measurements, and (ii) development of a manual for such measurements. The outreach activities include expansion of the local symposium (JSEHS) for high school teachers and students and hosting 10th and 11th grade students at the PI?s group during summer months.The proposed research will quantify different types of gas transport on small length scales and establish a quantitative relationship between these types of transport and macroscopic long range diffusion in porous membranes and related materials. Molecular fluxes through macroscopic porous systems are determined by long-range diffusivities. Hence, new knowledge generated in the proposed research will enable designing concrete strategies for optimizing gas fluxes in porous membranes while preserving separation selectivities.