The Dynamics of Organic Films on Different Time Scales

本计画主要研究吸附于固体表面之有机薄膜之结构、相变及动力学。它专注于烷烃[CnH2n+2]的薄膜，这种柔性链状分子在材料科学中具有普遍的兴趣，作为涂料，粘合剂和电子设备中使用的更复杂聚合物的原型。烷烃也是商业润滑剂的主要成分。 因此，对固体界面附近烷烃的结构和动力学性质的微观理解可能会导致基于聚合物的技术，特别是润滑技术的重大进展。拟议的研究是集中在准弹性中子散射（QNS）实验，调查分子扩散运动发生在一个范围内的时间尺度（皮秒至纳秒）的线性和支链烷烃的中间长度（20至40个碳原子）吸附在良好表征的石墨基板的薄膜。这些实验将在国家标准和技术研究所的最先进的中子谱仪上进行。他们将补充测量的纳米级烷烃膜形貌和横向摩擦力的原子力显微镜（AFM）。我们正在寻找由原子力显微镜测量的摩擦力和高能量分辨率QNS光谱所揭示的分子构象动力学之间的关系。由于动态实验的解释需要薄膜结构的知识，该项目包括结构研究，利用同步加速器X射线散射在阿贡国家实验室以及中子衍射在密苏里州大学研究反应堆。该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正在扩大的中子和X射线散射国家设施中的职业生涯做好准备。该项目涉及沉积在固体表面上的有机膜内发生的结构和分子运动。它专注于烷烃薄膜，柔性链状分子，在材料科学中作为涂料，粘合剂和电子设备中使用的更复杂聚合物的原型。烷烃也是商业润滑剂的主要成分。 对烷烃膜的结构和动力学性质的微观理解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。拟议的研究是集中在准弹性中子散射实验，调查分子运动发生在一个范围内的时间尺度（皮秒至纳秒）的烷烃薄膜吸附在良好的表征表面。这些实验将在国家标准和技术研究所的最先进的中子谱仪上进行。他们将通过原子力显微镜测量纳米级烷烃膜的形貌和横向摩擦力来补充。我们正在寻找这些纳米级的摩擦力和高能量分辨率的中子散射测量所揭示的分子运动之间的关系。由于动态实验的解释需要薄膜结构的知识，该项目包括结构研究，利用同步加速器X射线散射在阿贡国家实验室以及中子衍射在密苏里州大学研究反应堆。这项研究将为研究生提供聚合物科学基础方面的培训，为他们在工业以及我们不断扩大的中子和X射线散射国家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.