Wettabilities of Self-Assembled Monolayers Generated from CF 3 -Terminated Alkanethiols on Gold

Self-assembled monolayers of terminally fluorinated alkanethiols, CF 3 (CH 2 ) n SH with n = 9−15, and their nonfluorinated analogues, CH 3 (CH 2 ) n SH with n = 9−15, were prepared by adsorption from solution onto evaporated gold. The monolayers were characterized by contact angle goniometry, ellipsometry, and X-ray photoelectron spectroscopy. The analyses indicate that the CF 3 -terminated alkanethiols generate terminally fluorinated monolayers that are well-ordered, particularly when the chain lengths consist of 12 or more carbon atoms. Comparison of CF 3 -terminated films to CH 3 -terminated films of similar length reveals that terminal fluorination of the surface leads to an overall decrease in the surface tension of the films. This decrease arises from a relatively large decrease in the dispersive component of the surface tension upon the introduction of fluorine. Surprisingly, terminal fluorination also leads to a small but significant increase in the nondispersive component(s) of the surface tension. The origin of these opposing effects is discussed.