Understanding Vibrational Spectroscopic Probes of the Structure and Dynamics of Liquids Confined in Mesoporous Materials

堪萨斯大学的沃德·汤普森教授正在接受高分子、超分子和纳米化学项目颁发的奖项。在获奖项目中使用了理论和计算方法，以探索振动光谱技术可以揭示限制在不同大小(直径~2.4到4.5 nm)和表面官能度(羟基和烷基端基)的纳米二氧化硅孔中的液体和溶液的性质。在这种纳米尺度的限制下，分子级液体的结构和动力学发生了巨大的变化，但这些效应在线性红外(IR)光谱中并不容易观察到。通过分析振动光谱探测器，这个项目揭示了纳米受限液体的复杂结构和动力学。该项目的重点是密闭乙腈和相关系统。应用程序的选择是基于氢键时CN伸缩频率的显著蓝移和相对缓慢的振动弛豫，这允许检查更长的时间标度动力学。选择的方法包括分子动力学、宏正则蒙特卡罗模拟、电子结构计算和混合量子经典分子动力学方法。拟研究的性质包括：i)确定氰化物和异腈的线性红外光谱中氢键和非氢键峰的相对强度，ii)预测受限于不同表面化学的二氧化硅孔中的CH3CN的红外泵浦-探测光谱，iii)预测受限于不同表面化学的二氧化硅孔中的CH3CN的红外光子回波光谱，以及iv)模拟纳米受限的CH3CN中的溶质光谱和其他纳米受限液体中的CH3CN溶质的光谱。多孔二氧化硅材料在催化、分离和传感方面具有重要意义，是一类在各种应用中同样重要的多孔氧化物材料的一部分。此外，纳米受限液体还存在于许多其他系统中，包括超分子组装、模板材料、反胶束、生物系统、水凝胶、膜、燃料电池电极和非线性光学材料。该项目的更广泛的影响目标是从机制上更深入地了解液体如何在纳米受限结构中移动和相互作用，以及如何通过光谱学来探索这些机制，以帮助设计和表征在受限环境中利用液体的独特物理性质的应用程序。研究生和本科生都参与了这项研究，为他们提供了理论和计算技术方面的培训，并具有广泛的物理化学背景。在本研究小组内，继续鼓励任职人数不足的群体参加。

Professor Ward Thompson of the University of Kansas is receiving an award from the Macromolecular, Supramolecular and Nanochemistry Program. Theoretical and computational approaches are used in the awarded project for inquiring what vibrational spectroscopic techniques can reveal about the properties of liquids and solutions confined in nanoscale silica pores of varying size (~2.4 to 4.5 nm in diameter) and surface functionality (hydroxyl- and alkyl-terminated). Dramatic changes in the molecular-level liquid structure and dynamics occur upon such nanoscale confinement, yet these effects are not readily observable in the linear infrared (IR) spectra. By analyzing vibrational spectroscopic probes, this project sheds light on the complex structure and dynamics of nanoconfined liquids. The project focuses on confined acetonitrile and related systems. The application choice is based on the presence of a dramatic blue shift in the CN stretching frequency upon hydrogen bonding and the relatively slow vibration relaxation, which permits examination of longer timescale dynamics. A combination of molecular dynamics, grand canonical Monte Carlo simulations, electronic structure calculations, and mixed quantum-classical MD are the chosen methodologies. The proposed properties to be studied include: i) determination of the relative intensities of hydrogen bonded and non-hydrogen bonded peaks in the linear infrared spectra of nitriles and isonitriles, ii) prediction of the IR pump-probe spectroscopy of CH3CN confined in silica pores of varying surface chemistry, iii) prediction of the IR photon echo spectroscopy of CH3CN confined in silica pores of varying surface chemistry, and iv) simulation of the spectroscopy of solutes in nanoconfined CH3CN and of a CH3CN solute in other nanoconfined liquids.Porous silica materials are of interest in catalysis, separations, and sensing and are part of a wider class of porous oxide materials similarly important in a variety of applications. Moreover, nanoconfined liquids are present in a number of other systems including supramolecular assemblies, templated materials, reverse micelles, biological systems, hydrogels, membranes, fuel cell electrodes, and nonlinear optical materials. The broader impact aim of this project is to gain deeper mechanistic understanding of how liquids move and interact within nanoconfined structures and how these mechanisms can be probed via spectroscopy to assist in the design and characterization of applications that exploit the unique physical properties of liquids in confined environments. Graduate and undergraduate students are involved in this research, providing them with training in theoretical and computational techniques and a broad background in physical chemistry. The participation of underrepresented groups continues to be encouraged within this research group.