Self-assembled monolayers of alkanethiols on gold: the adsorption and wetting properties of monolayers derived from two components with alkane chains of different lengths

This paper describes the preparation and wetting properties of two-component self-assembled monolayers (SAMs) obtained by the competitive adsorption of one short-chain (HS(CH2)10Sh) and one long-chain (HS(CH2)21Lg) alkanethiol onto gold from dilute ethanolic solutions. The four possible combinations of the tail groups CH3 and CH2OH were investigated: Sh = CH3/Lg = CH2OH, Sh = CH2OH/Lg = CH3, Sh = CH2OH/Lg = CH2OH, and Sh = CH3/Lg = CH,. The compositions of these SAMs are not the same as the compositions of the solutions from which they were formed. Although the relationship between the composition of the SAM and the composition of the solution suggests that some phase separation may be occurring within the SAM, contact angles with water and hexadecane show that significant disorder still remains in the interfacial region.