CAREER: Crossing and Controlling the Bulk to Interface Transition: Chemical Profiles of Fluids Near Surfaces

在这项由化学结构、动力学和机制-化学系计划支持的项目中，爱荷华大学的Scott Shaw教授和他的学生正在使用各种光学工具(包括基于激光的技术)来表征吸附在固体材料表面或附近的分子的结构和动力学。这项研究中的一个关键工具是动态润湿(DW)设备，它可以生成厚度从一纳米到几微米(一英寸的百万分之二十五到千分之几英寸)的可控液体的薄膜。通过测量薄膜厚度变化时对光(尤其是红外光)的吸收，可以推断出最接近表面的分子的化学和结构信息。从这项研究中获得的信息和见解对化学研究的其他领域以及催化、腐蚀、润滑和半导体加工等应用技术都有影响。这项研究项目也是培养物理化学、激光技术和计算科学研究生和本科生的工具。推广活动包括Shaw教授的农村学者计划，该计划吸引来自农村地区有抱负的本科生进行真正的实验室研究体验。Shaw实验室采用的实验策略是围绕动态润湿(DW)技术开发的，该技术可产生厚度可控的分子流体膜，厚度从约1单层到近10微米。这种方法通过选择性地排除不透明的大块相，避免了直接观察界面的困难，并允许详细描述界面的形成和行为。通过和频(SFG)、偏振调制红外反射吸收光谱(PM-IRRAS)、拉曼光谱和变角椭圆偏振光谱等手段提取了流体膜的净分子取向和绝对厚度。实验光谱被用来基准和验证界面分子结构的计算模型和流体动力学模型。最终，这项研究可能会导致理解分子间力和几何限制在离表面特定距离处创建化学界面的作用，推动润滑、摩擦学和多相催化的基础研究。

In this project supported by the Chemical Structure, Dynamics and Mechanisms-A Program of the Division of Chemistry, Professor Scott Shaw and his students at the University of Iowa are employing a variety of optical tools (including laser-based techniques) to characterize the structure and dynamics of molecules adsorbed onto or near the surfaces of solid materials. A key tool in this research is a "dynamic wetting" (DW) apparatus, which can create films of liquids of controlled thicknesses from single nanometers to several microns (25 millionths of an inch to a few thousandths of an inch). By measuring the absorption of light (especially infrared light) as the film thickness is systematically varied, chemical and structural information about the molecules nearest the surface can be deduced. The information and insights gained from this research have impacts in other fields of chemistry research, as well as applied technologies such as catalysis, corrosion, lubrication, and semiconductor processing. This research project is also serving as a vehicle for the training of graduate and undergraduate students in physical chemistry, laser technology, and computational science. Outreach activities include Professor Shaw's Rural Scholars Program, which engages aspiring undergraduate students from rural areas in genuine laboratory research experiences.The experimental strategy employed in the Shaw laboratory is developed around the dynamic wetting (DW) technique, which creates molecular fluids films with controlled thicknesses from about one monolayer to nearly 10 microns thickness. This approach circumvents difficulties in direct observation of the interface by selectively excluding opaque, bulk phases, and allows detailed descriptions of interface formation and behaviors. The net molecular orientation and the absolute thickness of the fluid films are extracted by sum-frequency generation (SFG), infrared reflection-absorption spectroscopy (IRRAS) with polarization modulation (PM-IRRAS), Raman spectroscopy, and variable angle spectroscopic ellipsometry. The experimental spectra are used to benchmark and validate computational and fluid dynamic models of interfacial molecular structure. Ultimately, this research may lead to an understanding of the roles of intermolecular forces and geometric confinement in creating chemical interfaces at defined distances from surfaces, advancing fundamental research in lubrication, tribology, and heterogeneous catalysis.