Interfacial interactions between a carboxyl-terminated monolayer and various n-alcohols

The interactions of vapor-deposited methanol, ethanol, l-propanol, and 1-he xanol with an 11-mercaptoundecanoic acid (HOOC(CH2)(10)SH) self-assembled m onolayer adsorbed on a nickel(lll) single crystal were studied in ultrahigh vacuum by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The peak shapes of the TPD spectra for methanol, ethano l, and propanol desorption are similar, suggesting that these alcohols unde rgo similar desorption processes. Their peak desorption temperatures at the lowest submonolayer fluences increased with the number of carbons in the a lcohol, suggesting that the methyl and methylene groups, as well as the hyd roxyl group; participate in the adsorbed alcohol monolayer's interactions a t the acid-terminated self-assembled monolayer surface. Threshold TPD (TTPD ) was used for a quantitative analysis of the desorption spectra as a funct ion of coverage. The structure and behavior of hexanol's desorption spectra suggest a different desorption process than its lower-molecular-weight ana logues. Of all the alcohols studied, hexanol exhibited the strongest intera ction with the acid-terminated surface. The desorption energies calculated by the TTPD method for the straight-chain n-alcohols C-1-C-3 (15-20 kJ mol( -1)) and C-6 (similar to 38 kJ mol(-1)) in the submonolayer regime were in the range expected (10-40 kJ mol(-1)) for hydrogen bonding.