Synthesis and characterization of phenol- and o-chlorophenol-terminated monolayers

This paper describes the synthesis of phenol-terminated monolayers formed b y the chemisorption of precursor trichlorosilanes to silicate substrates an d subsequent in situ chemical transformations. A trichlorosilane containing an Ii-carbon polymethylene spacer and methyl-protected phenol was synthesi zed. The corresponding o-chlorophenol system was also synthesized. The mono layer structure was studied by a combination of reflectance FTIR,-X-ray ref lectometry, solid-state C-13 NMR spectroscopy, and water contact angles. Re action of the monolayers with BBr3 produced phenol-terminated monolayers. D ata obtained by contact angle titration using buffered solutions with pH va lues in the range of 1-14 was consistent with ionization of the surface-imm obilized phenol groups. The o-chlorophenol group exhibited a decrease in co ntact angles at lower pH values, which is consistent with a more acidic sur face. The phenol and o-chlorophenol exhibited pK(1/2) greater than or equal to 12.5 and greater than or equal to 12, which are at least 2.5 pH units h igher than the solution pK(a) values.