Adsorption Dynamics on Different Time Scales

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This individual investigator award will provide funds to a senior scientist for a project investigating the adsorption of polymers from a fluid mixture onto a solid surface. Whereas considerable progress has been made in understanding the structure and thermodynamics of such polymer films near interfaces, little is known of the microscopic dynamics of these systems. This project will investigate how polymer chains move so as to anchor, diffuse, and eventually desorb from a solid surface. The particular systems to be studied are linear and branched alkane molecules of intermediate size (20 and 40 carbon atoms) on graphite and Ag(111) substrates that serve both as interesting prototype systems and which contain the principal constituents of commercial lubricants. Quasielastic neutron scattering will be used to investigate the diffusive motion within the alkane films on time scales from picoseconds to tens of nanoseconds, while their static structure will be determined by neutron diffraction and synchrotron x-ray scattering. These experiments on alkane films will provide important tests of computer simulations of selective adsorption dynamics and may ultimately lead to the development of better engine oils. Graduate students will be trained in fundamental aspects of polymer science, preparing them for careers in the petroleum and rubber industries as well as at national facilities for neutron and synchrotron x-ray scattering. %%%Processes in which one chemical component in a fluid mixture preferentially sticks to a solid surface occur widely in materials science. Of particular interest is the selective adsorption from solution of long flexible-chain molecules, a process that is important in technological applications such as lubrication and adhesion. Whereas considerable progress has been made in understanding their structure and thermal properties, little is known about motion within these polymer films at the molecular level. This individual investigator award will provide funds to a senior scientist for a project investigating this issue. This project will investigate how polymer chains move so as to anchor, crawl about, and eventually depart from a solid surface. The particular systems to be studied are linear and branched alkane molecules of intermediate size (20 and 40 carbon atoms) on graphite and silver substrates that serve both as interesting prototype systems and contain the molecules that are the principal constituents of commercial lubricants. Quasielastic neutron scattering will be used to investigate the molecular motion within the alkane films on a wide range of time scales at the atomic level, while positions of the molecules will be determined by neutron diffraction and synchrotron x-ray scattering. These experiments on alkane films will provide important tests of computer simulations of selective adsorption dynamics and may ultimately lead to the development of better engine oils. Graduate students will be trained in fundamental aspects of polymer science, preparing them for careers in the petroleum and rubber industries as well as at national facilities for neutron and synchrotron x-ray scattering. ***