Reversible wettability of optothermal responsively perfluoroalkyl azobenzene self-assembled monolayers

<p>In this study, two perfluoroalkyl azobenzene trichlorosilanes were synthesized and then characterized by Fourier transform infrared spectroscopy (FT-IR), ¹H NMR, and ¹⁹F NMR. Subsequently, these fluorine containing trichlorosilanes were applied to form self-assembled monolayers (SAMs) on silicon substrates by the method of chemical deposition in liquid phase. The optothermal responsively isomerization of the azobenzene was achieved via UV irradiation and heat treatment. The surface structures of the SAMs were investigated by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The results showed that the thermal migration of the terminal fluoroalkyl groups promoted the isomerization of the azo-groups. Moreover, the reversible contact angles of the SAMs demonstrated a good reversibility of surface wettability, which was consistent with the optothermal responsive isomerization of the azo-groups.