Dynamics of Selective Adsorption

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9802476 Taub In this research program, Professors H. Taub and K.W. Herwig of the Department of Physics and Astronomy of the University of Missouri at Columbia will investigate processes in which one chemical component in a fluid mixture preferentially adsorbs on a solid surface. Such processes occur widely in materials science. A case of particular interest is the preferential adsorption from solution of long flexible-chain molecules, a process which is important in such applications as lubrication, adhesion, and coatings. Whereas considerable progress has been made in understanding the structure, thermodynamics, and, on macroscopic time scales, the kinetics of such polymers near interfaces, little is known of the dynamics of these systems at the atomic level. In simplest terms, the questions to be addressed are how do polymer chains move so as to anchor, diffuse, and eventually desorb from a solid surface. Both linear and branched alkane molecules of intermediate size (containing between 20 and 40 carbon atoms) on graphite and Ag(111) substrates will be used as prototype systems for studying the dynamics of selective adsorption. Quasielastic neutron scattering will be used to study the diffusive motion within the alkane films, while their structure will be investigated by neutron and synchrotron x-ray scattering. The interpretation of the experiments will be assisted by detailed computer simulations. Experiments will utilize existing state-of-the-art facilities at the Missouri University Research Reactor and both the Intense Pulsed Neutron Source and Advanced Photon Source at Argonne National Laboratory. %%% In this research program, Professors H. Taub and K.W. Herwig of the Department of Physics and Astronomy of the University of Missouri at Columbia will investigate processes in which one chemical component in a f luid mixture preferentially adsorbs on a solid surface. Such processes occur widely in materials science. A case of particular interest is the preferential adsorption from solution of long flexible-chain molecules, a process which is important in such applications as lubrication, adhesion, and coatings. Unfortunately very little is known at the microscopic level about the dynamics of how such polymer molecules anchor to a solid surface, then crawl about, and eventually desorb. In this project intermediate-length hydrocarbon-chain molecules (both linear and branched alkanes), which are the principal constituents of commercial lubricants, will be used as prototypes for studying the dynamics of selective adsorption. Quasielastic neutron scattering will be used to investigate the molecular motion within the hydrocarbon films, while their structure will be investigated by neutron and synchrotron x-ray scattering. The interpretation of the experiments will be assisted by detailed computer simulations. Experiments will utilize existing state-of- the-art facilities at the Missouri University Research Reactor and both the Intense Pulsed Neutron Source and Advanced Photon Source at Argonne National Laboratory. This research will provide training of graduate students in fundamental aspects of polymer science, preparing them for careers in the petroleum and rubber industries. ***