Aggregation structure and surface properties of immobilized organosilane monolayers prepared by the upward drawing method

Abstract

Octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] and [2-(perfluorooctyl)ethyl] trichlorosilane [FOETS, CF3(CF2)7CH2CH2SiCl3] monolayers were prepared on a water surface. The monolayers of OTS and FOETS amphiphiles were polymerized to form a Si–O–Si linkage on the water subphase. The polymerized monolayers were transferred onto a glass plate or silicon wafer surface by the upward drawing method and were covalently bonded to the Si–OH groups of the glass or silicon wafer surface. Electron diffraction patterns revealed that the OTS monolayer was in a crystalline state, while the FOETS monolayer was in an amorphous state at 293 K. The bright field image showed homogeneous molecular aggregation in the OTS and FOETS monolayers. The atomic force microscopic and frictional force microscopic images of the OTS/FOETS mixed monolayers distinctly showed a phase-separated structure. Deposition of the OTS, FOETS, and OTS/FOETS monolayers on the substrate was confirmed by attenuated total reflection Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. A highly hydrophobic property was observed for OTS, FOETS, and OTS/FOETS monolayer immobilized surfaces. Dynamic contact angle measurements indicated that the surface structure of these monolayers did not show reorganization upon environmental change because of polymerization and the formation of a covalent bond between the monolayer and the substrate surface.