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

Long-chain alkanoic acids (CH<INF>3</INF>(CH<INF>3</INF>)<INF>n</INF><INF></INF>CO<INF>2</INF>H, n > 15) form conformationally ordered monolayers on zirconium oxide powder via a chelating bidentate zirconium carboxylate surface bond. ω-Hydroxyalkanoic acids (HO(CH<INF>3</INF>)<INF>15</INF>CO<INF>2</INF>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.