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A novel 3-layer organic film was fabricated on silicon wafer with a polydopamine coating (coded as PDAc) as the interlayer by a multistep self-assembly process. The formation and structure of the films were analyzed by means of ellipsometric thickness measurement, water contact angle measurement, and attenuated total reflection-Fourier transform infrared spectrometry (ATR-FTIR). Meanwhile, an atomic force microscope (AFM) characterization was performed to evaluate the adhesive and microtribological behaviors of the 3-layer film, and a ball-on-plate tribometer was used to test macrotribological performance. As results show, the as-prepared 3-layer film possessed the excellent tribological properties characterized by lower friction and higher antiwear ability, which was ascribed to the special chemical structure of the film, i.e., the strong adhesion of the film to the silicon wafer, the chemical bonding between the adjacent layers, the cross-linked structure of the PDAc interlayer, and the hydrophobicity, high flexibility, and high elasticity of the stearoyl chloride (STC) outer layer. Hopefully, the present work provides a feasible route to construct a multilayer film with excellent structural stability and tribological behavior. The titled multilayer film might find potential applications in boundary lubrication and many other areas.

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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).