Experimental validation of molecular simulation of water transport across zeolite membranes of nanoscale-thickness

流体在多孔介质中的传输与从地下提取石油、地下水中的污染物传输、地下水库中二氧化碳的封存以及通过反渗透膜淡化海水以生产饮用水有关。多孔介质提供了对质量传输的阻力。化学物种之间的阻力差异允许分离：一种成分可能不受阻碍，甚至可能被加速，而另一种成分则受到阻碍。例如，反渗透膜的设计可以非常有效地输送水，但输送盐分的效率很低，从而导致生产纯净的饮用水。为了优化设计，工程渗流输运模型一般使用宏观长度尺度和平均阻力来处理系统，但通常忽略了分子尺度上的空间变化和特定的流面相互作用。当流体分子被限制在具有相似分子尺寸的孔中时，分子尺度的相互作用变得非常明显。解释分子相互作用的模型包含了力场，但没有充分预测实验观测结果。这个项目将对分子水平通过具有强烈流体-孔隙相互作用的多孔材料的传输进行实验验证，并将首次在实验和理论研究之间进行一对一的长度尺度对应，以探索差异。在这个项目中，通过沸石膜进行海水淡化是探针系统，这是因为水-沸石之间的强烈静电相互作用在限制在亚纳米(~0.56 nm)孔中时会得到增强。具有不同铝组成和厚度(从纳米到微米)的MFI分子筛将被实验合成和表征，然后转移到载体表面，以在定制的实验装置中创建用于传输测量的膜。分子动力学模拟将同时对具有不同力场的相同沸石进行。在这两种技术中，铝含量都会不同，以改变水-沸石的相互作用。经过实验验证的分子模型将提供对受限孔隙中水相互作用的基本理解，并有助于开发预测水在纳米多孔材料中的热力学性质和传输行为的模型。该项目包括几个推广部分，包括针对未被充分代表的少数群体的本科生研究项目，为中学生举办的研讨会，以及为锡拉丘兹大学的本科生开设的计算方法短期课程。

Transport of a fluid in porous media is relevant to extraction of oil from the subsurface, contaminant transport in groundwater, sequestration of carbon dioxide in underground reservoirs, and desalination of seawater through a reverse osmosis membrane to produce drinking water. The porous media offers a resistance to the transport of mass. Differences in resistance between chemical species allow for separation: one component may be unimpeded or even accelerated, while another is impeded. For example, the reverse osmosis membrane is designed to transport water quite efficiently but transport salt quite inefficiently, leading to the production of purified drinking water. To optimize design, engineering transport models of flow through porous media generally treat the system using macroscopic length scales and average resistances, but generally neglect both spatial variations and specific fluid-surface interactions on the molecular scale. Molecular-scale interactions become quite pronounced when a fluid molecule is confined in a pore that is of similar molecular dimension. Models that account for molecular interactions incorporate forcefields, but have not adequately predicted experimental observations. This project will perform an experimental validation of molecular-level transport through a porous material with strong fluid-pore interactions, and for the first time, there will be a one-to-one length scale correspondence between the experimental and theoretical studies which will probe discrepancies. In this project, desalination of seawater through a zeolite membrane is the probe system, due to strong water-zeolite electrostatic interactions that are enhanced upon confinement in sub-nanometer (~0.56 nm) pores. MFI zeolites with varying aluminum composition and thickness (varying from nano- to micro-scale) will be experimentally synthesized and characterized, then transferred onto a support surface to create membranes for transport measurements in a custom-built experimental apparatus. MD simulations will be simultaneously performed for the same zeolites with varying forcefields. The aluminum content will be varied in both techniques to alter the water-zeolite interaction. The experimentally validated molecular models will provide fundamental understanding of water interaction in confined pores, and assist in the development of predictive modeling of thermodynamic properties and transport behavior of water in nano-porous materials. The project includes several outreach components, including undergraduate research projects that target under-represented minorities, a workshop for middle school female students, and a short course in computational methods for undergraduates at Syracuse University.