Preparation and Tribological Studies of Stearic Acid Self-Assembled Monolayers on Polymer-Coated Silicon Surface

Abstract

We present a good alternative method to improve the tribological properties of polymer films by chemisorbing a long-chain monolayer on the functional polymer surface. Thus, a novel self-assembled monolayer is successfully prepared on a silicon substrate coated with amino-group-containing polyethyleneimine (PEI) by the chemical adsorption of stearic acid (STA) molecules. The formation and structure of the STA-PEI film are characterized by means of contact-angle measurement and ellipsometric thickness measurement, and of Fourier transformation infrared spectrometric and atomic force microscopic analyses. The micro-and macro-tribological properties of the STA-PEI film are investigated on an atomic force microscope (AFM) and a unidirectional tribometer, respectively. It has been found that the STA monolayer about 2.1-nm thick is produced on the PEI coating by the chemical reaction between the amino groups in the PEI and the carboxyl group in the STA molecules to form a covalent amide bond in the presence of N,N′-dicyclohexylcarbodiimide (DCCD) as a dehydrating regent. By introducing the STA monolayer, the hydrophilic PEI polymer surface becomes hydrophobic with a water contact angle to be about 105°. Study of the time dependence of the film formation shows that the adsorption of PEI is fast, whereas at least 24 h is needed to generate the saturated STA monolayer. Whereas the PEI coating has relatively high adhesion, friction, and poor anti-wear ability, the STA-PEI film possesses good adhesive resistance and high load-carrying capacity and anti-wear ability, which could be attributed to the chemical structure of the STA-PEI thin film. It is assumed that the hydrogen bonds between the molecules of the STA-PEI film act to stabilize the film and can be restored after breaking during sliding. Thus, the self-assembled STA-PEI thin film might find promising application in the lubrication of micro-electromechanical systems (MEMS).

Chemical and Structural Properties of Polyethyleneimine Film Coated on a SiO₂ Substrate in Different Concentrations

“…1,2) Until now, (3-Aminopropyl)-triethoxysilane (APTES), 1) polyethyleneimine (PEI), 13) polyethyleneglycol (PEG) 4) and polyethylene (PE). 1,4) have been proposed as a surface linker material for the sensing or recognition of biological elements in biosensors. Among these materials, PEI has been considered as a viable surface linker owing to its simple controllability and biofunctionality.…”

Fabrication and characterization of Ag/polymer nanocomposite films through layer-by-layer self-assembly technique

“…The water contact angle for the PEImodified surface is 8°, characteristic of PEI monolayer covered surface [29]. After anionic PSS adsorption on the PEI surface, the contact angle increases to 36°.…”

Construction of Various Self-assembled Films and Their Application as Lubricant Coatings

“…A promising way to further ameliorate the tribological behaviors of SAMs, especially the load-carrying capacity, is to enhance the stability of the films. It is revealed that the SAMFs with synergetic components generally exhibits longer anti-wear life (Ren et al, 2003;Ren et al, 2004;a, Song et al, 2008). The reason for the enhanced wear resistance is ascribed to the special structures of the SAMFs.…”