title: Lubrication of Individual Microcontacts by a Self-Assembled Alkyl Phosphonic Acid Monolayer on α-Al2O3(0001).
abstract: We report on the tribological behavior of a self-assembled alkyl phosphonic acid monolayer on the microscale using the colloidal probe technique. Friction-load data and adhesion forces were measured with borosilicate glass particles on uncoated and octadecylphosphonic acid (ODPA) coated α-Al2O3(0001) surfaces. A significant decrease in friction force was observed after surface coating, while the adhesion force was only moderately reduced. We assume the lubrication effect of the ODPA self-assembled monolayer (SAM) to be close to the maximum obtainable of alkyl phosphonic acids in the studied system due to the high molecular order which was confirmed by vibrational sum-frequency generation. At small loads, a nonlinear dependence of friction force to load was maintained after surface coating. However, a shift from a contact behavior well described by the DMT model toward the JKR model occurred that is possibly related to the altered elastic properties of the coated surface. With increasing load, a linear friction-load behavior was observed on the coated samples. Molecular plowing and adhesive interactions were identified as responsible mechanisms. In all friction experiments, we could not detect any wear neither of the colloidal probes nor at the surfaces of uncoated and coated samples. This proves the high wear resistivity of the studied ODPA SAM.
authors.affiliation: Institute of Particle Technology (LFG), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Cauerstraße 4, 91058 Erlangen, Germany.
authors.forename: Jonas
authors.initials: J
authors.lastname: Paul
authors.affiliation: Institute of Particle Technology (LFG), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Cauerstraße 4, 91058 Erlangen, Germany.|Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Paul-Gordon-Strasse 6, 91052 Erlangen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Meltzer
authors.affiliation: Institute of Particle Technology (LFG), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Cauerstraße 4, 91058 Erlangen, Germany.|Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Paul-Gordon-Strasse 6, 91052 Erlangen, Germany.|Cluster of Excellence - Engineering of Advanced Materials (EAM), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Nägelsbachstrasse 49b, 91052 Erlangen, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Braunschweig
authors.affiliation: Institute of Particle Technology (LFG), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Cauerstraße 4, 91058 Erlangen, Germany.|Erlangen Graduate School in Advanced Optical Technologies (SAOT), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Paul-Gordon-Strasse 6, 91052 Erlangen, Germany.|Cluster of Excellence - Engineering of Advanced Materials (EAM), Friedrich-Alexander University of Erlangen-Nürnberg (FAU) , Nägelsbachstrasse 49b, 91052 Erlangen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Peukert