Static solvent contact angle measurements, surface free energy and wettability determination of various self-assembled monolayers on silicon dioxide

In many fields and applications, a good knowledge of the wetting behaviour of solvents on a surface is crucial. Self-assembled monolayers (SAMs) have enabled improved control over surface properties, while more recent fields such as organic electronics gave rise to new applications and requirements regarding solvent-substrate interactions. However, most reported wettability studies are limited to practically less relevant solvents such as water, diiodomethane or hexadecane. Herein we report static contact angle measurements of various, typical SAM-modified surfaces, characterizing these surfaces' wettabilities over a wide range of practically relevant solvents. Surface energies, both the polar and the disperse component, of these SAM-modified surfaces are extracted with various methods from the contact angle data. Reliable methods for surface energy extraction, such as the Owens-Wendt-Rabel-Kaelble method and the method after Wu, yield values which could be expected from the chemical structure and nature of the self-assembled molecules and which correspond well to the few reported literature values. We also determined wetting envelopes for the various surfaces which allow easy prediction of the surfaces' wettability for a certain solvent and which ensure relevance for current and future solvents. (c) 2006 Elsevier B.V. All rights reserved.