Structure of adsorbed n-dodecyl-beta-D-maltoside layers on hematite

The composition, structure, and thickness of n-dodecyl-beta-D-maltoside self-assembled layers on hematite have been evaluated using infrared external reflection spectroscopy and spectral simulation techniques. From the qualitative and quantitative analysis of the reflection spectra of the same sample recorded at different specific angles of incidence and two polarizations, the orientation of the sugar ring and hydrocarbon chain were obtained. Both of these molecular groups are positioned parallel to hematite surface, the adsorbed molecules being at low (2.2-nm-thick layer) as well as higher (11-nm) coverages. The maltoside is adsorbed through interaction of sugar ring OH groups with hematite surface hydroxyl groups. The adsorption of maltoside is not very strong and desorption takes place easily from acidic and low-basic solutions but with more difficulty from strong-basic solution.