The Dynamics of Organic Films on Different Time Scales

本项目研究吸附在固体表面的有机薄膜的结构、相变和动力学。它侧重于烷烃[CnH2n+2]的薄膜，这是材料科学中普遍感兴趣的柔性链状分子，作为用于涂料、粘合剂和电子设备的更复杂聚合物的原型。烷烃也是商业润滑油的主要成分。因此，对固体界面附近烷烃结构和动力学性质的微观了解可能会导致基于聚合物的技术的重大进步，特别是润滑。这项研究以准弹性中子散射(QNS)实验为中心，研究了中等长度的直链烷烃和支链烷烃(碳原子20到40个碳原子)在一系列时间尺度(皮秒到纳秒)内的分子扩散运动。这些实验将在美国国家标准与技术研究所最先进的中子谱仪上进行。此外，还将利用原子力显微镜(AFM)测量纳米级烷烃薄膜的形貌和侧向摩擦力。我们正在寻找原子力显微镜测量的摩擦力与高能分辨量子谱揭示的分子构象动力学之间的关系。由于对动力学实验的解释需要对薄膜结构的了解，该项目包括阿贡国家实验室利用同步加速器x射线散射进行的结构研究以及密苏里大学研究反应堆的中子衍射。这项研究将为研究生提供聚合物科学基础方面的培训，为他们在工业和学术界以及我们不断扩大的国家中子和X射线散射设施中的职业生涯做好准备。该项目涉及沉积到固体表面上的有机薄膜中发生的结构和分子运动。它侧重于烷烃薄膜，这是材料科学中普遍感兴趣的柔性链状分子，是用于涂料、粘合剂和电子设备的更复杂聚合物的原型。烷烃也是商业润滑油的主要成分。从微观上了解烷烃薄膜的结构和动力学性质，可能有助于从更耐用的聚合物涂层到减少发动机磨损的润滑剂等技术进步。拟议的研究集中在准弹性中子散射实验上，以研究在一段时间范围内(皮秒到纳秒)吸附在特征良好的表面上的烷烃薄膜中发生的分子运动。这些实验将在美国国家标准与技术研究所最先进的中子谱仪上进行。此外，原子力显微镜还将测量纳米级烷烃薄膜的形貌和侧向摩擦力。我们正在寻找这些纳米级摩擦力与高能分辨中子散射测量揭示的分子运动之间的关系。由于对动力学实验的解释需要对薄膜结构的了解，该项目包括阿贡国家实验室利用同步加速器x射线散射进行的结构研究以及密苏里大学研究反应堆的中子衍射。这项研究将为研究生提供聚合物科学基础方面的培训，为他们在工业和我们不断扩大的国家中子和X射线散射设施中的职业生涯做好准备。

This project is concerned with the structure, phase transitions, and dynamics of organic films adsorbed on solid surfaces. It focuses on films of alkanes [CnH2n+2], flexible chain-like molecules that are of general interest in materials science as prototypes of more complex polymers used in coatings, adhesives, and electronic devices. Alkanes are also the principal constituents of commercial lubricants. Thus a microscopic understanding of the structural and dynamical properties of alkanes near solid interfaces could potentially lead to significant advances in polymer-based technologies, particularly lubrication. The proposed research is centered on quasielastic neutron scattering (QNS) experiments to investigate the molecular diffusive motion that occurs over a range of time scales (picoseconds to nanoseconds) in films of both linear and branched alkanes of intermediate length (20 to 40 carbon atoms) adsorbed on well-characterized graphite substrates. These experiments will be conducted on state-of-the-art neutron spectrometers at the National Institute of Standards and Technology. They will be complemented by measurement of the nanoscale alkane film topography and lateral frictional forces by Atomic Force Microscopy (AFM). We are seeking relations between the frictional forces measured by AFM and the molecular conformational dynamics as revealed by the high-energy-resolution QNS spectra. Since interpretation of the dynamical experiments requires knowledge of the film structure, the project includes structural studies utilizing synchrotron x-ray scattering at Argonne National Laboratory as well as neutron diffraction at the University of Missouri Research Reactor. This research will provide training of graduate students in fundamental aspects of polymer science, preparing them for careers in industry and academia as well as at our expanding national facilities for neutron and x-ray scattering.This project is concerned with the structure and molecular motions that occur within organic films that are deposited onto to solid surfaces. It focuses on films of alkanes, flexible chain-like molecules that are of general interest in materials science as prototypes of more complex polymers used in coatings, adhesives, and electronic devices. Alkanes are also the principal constituents of commercial lubricants. A microscopic understanding of the structural and dynamical properties of alkanes films could contribute to technological advances ranging from more durable polymer coatings to lubricants that reduce engine wear. The proposed research is centered on quasielastic neutron scattering experiments to investigate the molecular motions that occur over a range of time scales (picoseconds to nanoseconds) in alkane films adsorbed on well-characterized surfaces. These experiments will be conducted on state-of-the-art neutron spectrometers at the National Institute of Standards and Technology. They will be complemented by measurement of the nanoscale alkane film topography and lateral frictional forces by Atomic Force Microscopy. We are seeking relations between these nanoscale frictional forces and the molecular motion as revealed by the high-energy-resolution neutron scattering measurements. Since interpretation of the dynamical experiments requires knowledge of the film structure, the project includes structural studies utilizing synchrotron x-ray scattering at Argonne National Laboratory as well as neutron diffraction at the University of Missouri Research Reactor. This research will provide training of graduate students in fundamental aspects of polymer science, preparing them for careers in industry as well as at our expanding national facilities for neutron and x-ray scattering.