SAMs on Gold Derived from Adsorbates Having Phenyl and Cyclohexyl Tail Groups Mixed with Their Phase-Incompatible Fluorinated Analogues.

Abstract

This article investigates two types of mixed self-assembled monolayers (SAMs) derived from adsorbates having cyclohexyl and phenyl tail groups mixed with their perfluorinated analogues. The mixed SAMs were characterized using ellipsometry, X-ray photoelectron spectroscopy (XPS), polarization-modulation infrared reflection absorption spectroscopy, and contact angle measurements. The XPS results show preferential adsorption of the nonfluorinated adsorbate in the perfluorocyclohexyl-terminated/cyclohexyl-terminated pair due to the steric bulk of the tail groups. On the other hand, mixed surfaces with a precisely controlled surface composition were achieved with the phenyl-terminated/perfluorophenyl-terminated mixed SAMs, exhibiting a linear relationship between the mole fraction on the surface and the mole fraction in solution. The results suggest that the relative solubility, steric bulk of the tail group moiety, and the interaction between two different adsorbates are the key factors driving the phase phenomena observed in the SAMs. More importantly, this study suggests that the interfacial properties can be controlled with a minimal loss of packing densities with the phenyl-terminated/perfluorophenyl-terminated mixed SAMs.