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 alkylthiols and disulfides chemisorbed on an Au(111) single crystal surface were used as substrate for subsequent temperature programmed desorption (TPD) studies. The monolayers studied were derived from adsorbates of the general structure HS(CH sub 2) sub (15) X or (S(CH sub 2) sub (15) X) sub 2 (where X=CH sub 3, CO sub 2 CH sub 3, CH sub 2 OH, CO sub 2 H, and CONH sub 2). 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 behaviors for the adsorption of secondary overlayers on these dense molecular solid 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.