title: Depletion at solid/liquid interfaces: flowing hexadecane on functionalized surfaces.
abstract: We present a neutron reflectivity study on interfaces in contact with flowing hexadecane, which is known to exhibit surface slip on functionalized solid surfaces. The single crystalline silicon substrates were either chemically cleaned Si(100) or Si(100) coated by octadecyl-trichlorosilane (OTS), which resulted in different interfacial energies. The liquid was sheared in situ and changes in reflectivity profiles were compared to the static case. For the OTS surface, the temperature dependence was also recorded. For both types of interfaces, density depletion of the liquid at the interface was observed. In the case of the bare Si substrate, shear load altered the structure of the depletion layer, whereas for the OTS covered surface no effect of shear was observed. Possible links between the depletion layer and surface slip are discussed. The results show that, in contrast to water, for hexadecane the enhancement of the depletion layer with temperature and interfacial energy reduces the amount of slip. Thus a density depletion cannot be the origin of surface slip in this system.
authors.affiliation: Institut für Festkörperphysik, Ruhr-Universität Bochum, 44780 Bochum, Germany. gutfreund@ill.eu
authors.forename: Philipp
authors.initials: P
authors.lastname: Gutfreund
authors.forename: Max
authors.initials: M
authors.lastname: Wolff
authors.forename: Marco
authors.initials: M
authors.lastname: Maccarini
authors.forename: Stefan
authors.initials: S
authors.lastname: Gerth
authors.forename: John F
authors.initials: JF
authors.lastname: Ankner
authors.forename: Jim
authors.initials: J
authors.lastname: Browning
authors.forename: Candice E
authors.initials: CE
authors.lastname: Halbert
authors.forename: Hanna
authors.initials: H
authors.lastname: Wacklin
authors.forename: Hartmut
authors.initials: H
authors.lastname: Zabel