WETTABILITIES OF SELF-ASSEMBLED MONOLAYERS GENERATED FROM CF3-TERMINATED ALKANETHIOLS ON GOLD

Self-assembled monolayers of terminally fluorinated alkanethiols, CF3( CH2)(n)SH with n = 9-15, and their nonfluorinated analogues, CH3(CH2)( n)SH with n = 9-15, were prepared by adsorption from solution onto eva porated gold. The monolayers were characterized by contact angle gonio metry, ellipsometry, and X-ray photoelectron spectroscopy. The analyse s indicate that the CF3-terminated alkanethiols generate terminally fl uorinated monolayers that are well-ordered, particularly when the chai n lengths consist of 12 or more carbon atoms. Comparison of CF3-termin ated films to CH3-terminated films of similar length reveals that term inal fluorination of the surface leads to an overall decrease in the s urface tension of the films. This decrease arises from a relatively la rge decrease in the dispersive component of the surface tension upon t he introduction of fluorine. Surprisingly, terminal fluorination also leads to a small but significant increase in the nondispersive compone nt(s) of the surface tension. The origin of these opposing effects is discussed.