The Dynamics of Organic Films on Different Time Scales

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.