Self-Assembled Monolayers of Alkanoic Acids:  A Solid-State NMR Study

Abstract

Long-chain alkanoic acids (CH 3 (CH 3 ) n CO 2 H, n > 15) form conformationally ordered monolayers on zirconium oxide powder via a chelating bidentate zirconium carboxylate surface bond. ω-Hydroxyalkanoic acids (HO(CH 3 ) 15 CO 2 H) produce hydrophilic monolayers, with no evidence of looping to the metal oxide surface. Variable temperature and two-dimensional solid-state NMR experiments demonstrate that alkanoate monolayers display chain dynamics similar to other self-assembled monolayers (SAMs). The thermal behavior of alkanoate SAMs is also compared to analogous fatty acid salt Langmuir−Blodgett monolayers which undergo pretransitional chain disordering.