Synthesis and Characterization of Phenol- and o-Chlorophenol-Terminated Monolayers

This paper describes the synthesis of phenol-terminated monolayers formed by the chemisorption of precursor trichlorosilanes to silicate substrates and subsequent in situ chemical transformations. A trichlorosilane containing an 11-carbon polymethylene spacer and methyl-protected phenol was synthesized. The corresponding o -chlorophenol system was also synthesized. The monolayer structure was studied by a combination of reflectance FTIR, X-ray reflectometry, solid-state 13 C NMR spectroscopy, and water contact angles. Reaction of the monolayers with BBr 3 produced phenol-terminated monolayers. Data obtained by contact angle titration using buffered solutions with pH values in the range of 1−14 was consistent with ionization of the surface-immobilized phenol groups. The o -chlorophenol group exhibited a decrease in contact angles at lower pH values, which is consistent with a more acidic surface. The phenol and o -chlorophenol exhibited p K 1/2 ≥ 12.5 and ≥ 12, which are at least 2.5 pH units higher than the solution p K a values.