Preparation and micro-mechanical studies of polysiloxane-containing dual-layer film on Au surface

A novel polysiloxane-containing self-assembled dual-layer film was grafted onto Au surface with a simple three-step method. Firstly, (3-mercaptopropyl)trimethoxysilane (MPTMS) molecules were self-assembled on Au surfaces through S–Au bond followed by hydrolysis and condensation, then the octadecyltrichlorosilane molecules were attached to the resultant hydroxyl terminated surface via the Si–O–Si bonds. The structure and morphology of the film were characterized by means of contact angle measurement, ellipsometry, attenuated total reflectance Fourier transformed infrared spectra, and atomic force microscopy. The resistant ability of charge transfer in the film forming process was detected by electrochemical techniques. Using force–volume technique, we investigated how the different surface chemical groups influence the surface adhesion properties. The nano-friction properties of the as-prepared films were investigated by frictional force microscopy. The results indicated that the dual-layer film fabricated via the hydrolyzation of MPTMS underlayer had significantly less friction. Moreover, compared to the self-assembled monolayer of octadecane thiol, the resultant dual-layer film showed much less wear. This improvement was mainly ascribed to the existence of the network of lateral cross-linked polysiloxane layer within the film which can enhance the stability of the film.