Order of Dry and Wet Mixed-Length Self-Assembled Monolayers

Abstract

Functionalizing the surface of metal and oxide materials with self-assembled monolayers is an elegant method for tuning the chemical properties of the surfaces. The properties of a coated surface depend on both the chemical nature of the termination as well as the order of the monolayer. One commonly used platform is alkylsilanes on silica surfaces. Here we characterize the disorder of self-assembled monolayers having a mixture of two monomer lengths using sum-frequency generation (SFG) and Fourier transform infrared spectroscopy. We find that mixed monolayer order varies smoothly as a function of composition. The mixed monolayers are more disordered than either pure monolayer, and of the pure monolayers, the shorter monolayer is more disordered. The nonlinear relationship between monolayer disorder and composition, along with atomic force microscopy images, suggests completely homogeneous mixing or very small domains of the monomers. The order of the monolayers as determined by SFG spectroscopy does not ...