Studies of molecular orientation and order in self-assembled semifluorinated n-alkanethiols: Single and dual component mixtures

The structure, orientation and morphology of self-assembled monolayers of a semifluorinated n-alkanethiol, F(CF2)(8)(CH2)(11)SH (F8H11SH), have been investigated by polarized IR, angular dependent XPS, ToF-SIMS, contact angle, and ellipsometric measurements. The orientation of the all trans hydrocarbon segment was found to be tilted much less from the surface normal than the 30 degrees tilt found for octadecanethiol. This has been attributed to the steric constraints imposed by the larger cross section fluorocarbon helices that subsequently are tilted from the surface normal. In addition, studies of dual component mixtures of F8B11SH/F8SH and F8SH/F8H2SH have revealed that competitive adsorption occurs in the farmer, producing monolayers that are deficient in the shorter F8SH molecules, while in the latter equal representation of both F8SH and F8H2SH molecules are found on the surface due to their similar molecular lengths.