Interfacial chemistry on carboxylate‐functionalized monolayer assemblies

AbstractDeposition of trichlorosilanes with ester groups at their remote termini provides a convenient entry to carboxylic acid‐bearing siloxane‐anchored self‐assembled monolayers. The de‐esterification of these esters has been optimized to minimize monolayer damage, and their quantitative re‐esterification provides clear evidence for the stability of these systems. Both the structure of the ester‐terminated monolayer and its de‐esterification/esterification chemistry can be easily monitored by FTIR‐ATR measurements. This spectroscopic tool, together with a liquid cell that enables IR spectra to be measured in an aqueous environment, enables a detailed structural analysis of the carboxylic acid‐bearing siloxane‐anchored self‐assembled monolayers and an assessment of their acid/base behavior (by in situ titration). The use of D2O instead of H2O for the in situ titration experiments also improves the available IR window. Both monomeric and dimeric/oligomeric acid groups are seen, and the relative ease of deprotonation of these various species can be directly monitored. Monomers of alkyl carboxylic acids that are hydrogen bonded only to surrounding water molecules have a pKa = 4.9, wh