Synthesis of branched gem-bisfluoroalkylsilane with short-chain perfluoroalkyl moieties and its self-assembled monolayers

In this study, two novel perfluoroalkylsilane monomers with branched bisfluoroalkyl moieties were synthesized via Radical Addition and Hydrosilylation. Their structure was characterized by FT-IR and 1H NMR Fluoroalkyl-terminated self-assembled monolayers (SAMs) on silanol-terminated silicon substrates were chemically fabricated via –Si–O– covalent bonding with the liquid phase deposition method (LPD). The wettabilities of the SAMs were characterized by Water Contact Angles (WCA) and surface free energies measurements. X-ray Photoelectron Spectroscopy (XPS) was used to validate the attachment, together with the chemical composition of the SAMs on the silicon substrate. The surface morphologies and roughness of the monolayers were obtained through Atomic Force Microscopy (AFM). It was found that the SAMs of perfluoroalkylsilane has higher contact angle and lower surface energy after heat treatment as the migration of fluoroalkyl groups to the outermost surface of the SAMs because of the surface microphase separation. Besides, on account of the strong π-π bonding between phenylene bridged group, the perfluoroalkylsilane monomer containing phenylene group exhibited denser structure and then the hydrophobicity of SAMs can be improved to some extent.