title: Order and composition of methyl-carboxyl and methyl-hydroxyl surface-chemical gradients.
abstract: A detailed infrared and XPS characterization of surface-chemical gradients of dodecanethiol with 11-mercaptoundecanol or 11-mercaptoundecanoic acid self-assembled on gold, is reported. Gradients were prepared using a simple, two-step process previously reported from our laboratory, which involves a controlled immersion of a polycrystalline gold substrate in a dilute (5 microM) solution of one component and a subsequent back-filling with the other. FTIR measurements show that a single-component gradient of dodecanethiol is composed of disordered, liquidlike alkyl chain conformations. Such a gradient, when back-filled with a complementary thiol, having either a hydroxyl or carboxyl end-group, yields two-component gradients that show similar changes in wettability along their lengths. However, while gradients composed of methyl and hydroxyl end-groups show a well-ordered alkyl chain structure over their entire length, methyl-carboxyl gradients exhibit a greater conformational disordering toward the carboxyl-rich end.
authors.affiliation: Laboratory for Surface Science and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
authors.forename: Nagaiyanallur V
authors.initials: NV
authors.lastname: Venkataraman
authors.forename: Stefan
authors.initials: S
authors.lastname: Zürcher
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Spencer