Octadecylphosphonic Acid Self-Assembled Monolayers as Lubricant Coatings Stable in Alkaline Media
- PDF / 423,201 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 81 Downloads / 167 Views
EE13.28.1
Octadecylphosphonic Acid Self-Assembled Monolayers as Lubricant Coatings Stable in Alkaline Media J. Soullier1,2, P. Tordjeman1, P.H. Mutin2 1 Laboratoire d’Analyse des Interfaces et de Nanophysique, UMR CNRS 5011 Université Montpellier 2, place Eugène Bataillon, 34095 Montpellier Cedex 5, France 2 Chimie Moléculaire et Organisation du Solide, UMR CNRS 5637 Université Montpellier 2, place Eugène Bataillon, 34095 Montpellier Cedex 5, France ABSTRACT The formation of octadecylphosphonic acid self-assembled monolayers (SAMs) on titanium deposited by cathodic sputtering on planar substrates has been studied by water contact angle measurements and Atomic Force Microscopy (AFM). Dense monolayers were obtained after one week of reaction. Tribological experiments indicated that these monolayers had good lubricating properties, which were maintained after immersion in a 1 M NaOH solution at 65 °C for up to 100 min. The stability in alkaline media of octadecylphosphonic acid SAMs on titanium was ascribed to the high chemical stability of Ti-O-P interfacial bonds.
INTRODUCTION Organophosphorus coupling molecules such as phosphonic acids (R-PO(OH)2) can be used to prepare covalent organic-inorganic hybrid solids, either by sol-gel processing [1] or by surface modification of a metal oxide support [2-4]. Formation of self-assembled monolayers (SAMs) is observed in the case of long-chain alkylphosphonic acids [5,6]. There has recently been much interest in SAMs as boundary layer lubricants in microelectro-mechanical systems (MEMS) [7-11] and magnetic storage systems [11,12], as SAMs are characterized by a low friction coefficient, a small thickness and a strong bonding with the substrate. Most of the tribological studies on self-assembled monolayers concern SAMs of alkane thiols (on gold, silver, etc.) [13,14] or of alkylsilanes (on oxidized silicon, glass, etc.) [9,10,14], while the tribology of phosphonic acid monolayers has only been studied on aluminum oxide substrates [15]. Phosphonic acids have an excellent affinity for titanium dioxide, and TiO2/PhPO3 hybrids prepared by sol-gel exhibited an exceptional stability in alkaline media [1]. According to 17O NMR experiments, the binding of phosphonic acids to titanium dioxide involves the formation of three Ti-O-P bonds [16]. In this communication we present a study on the formation and the tribological properties of octadecylphosphonic acid (ODPA) SAMs on a titanium coating (100 nm thick), deposited by cathodic sputtering. Friction coefficients were determined at the nanoscopic scale with an atomic force microscope in contact mode, and at the microscopic scale with a home-made tribometer. The kinetics of ODPA SAM formation and its stability in an alkaline media were investigated using water contact angle measurement, friction coefficient measurements, optical and atomic force microscopies.
EE13.28.2
EXPERIMENTAL DETAILS For this study we used planar substrates: microscope glass slides Gold Seal 3010 (7.5 x 2.5 cm, thickness 1 mm) coated by a 100 nm thick titanium
Data Loading...
