Fundamental Studies of Microscopic Wetting on Organic Surfaces. 2. Interaction of Secondary Adsorbates with Chemically Textured Organic Monolayers

Self-assembled monolayers of a series of terminally substituted alkyl thiols and disulfides chemisorbed on an Au(111) single-crystal surface were used as substrates for subsequent temperature-programmed desorption (TPD) studies. The monolayers studied were derived from adsorbates of the general structure HS(CH₂)₁₅X or (S(CH₂)₁₅X)₂ (where X = CH₃, CO₂CH₃, CH₂OH, CO₂H, and CONH₂). The adsorption of n-hexane, methanol, and water on these materials as well as on the clean Au(111) surface was examined. The data reveal complex behavior for the adsorption of secondary overlayers on these dense molecular solids especially in those substrate-adsorbate pairings capable of forming interlayer hydrogen bonds. It is also found that certain correlations can be made between the TPD data, a microscopic measurement, and the macroscopic wetting properties as defined by contact angle data.