Polarized Infrared Study of Hybrid Langmuir−Blodgett Monolayers Containing Clay Mineral Nanoparticles

• Published in: Langmuir Vol. 19; no. 10; pp. 4295 - 4302
• Main Authors: Ras, R. H. A., Johnston, C. T., Franses, E. I., Ramaekers, R., Maes, G., Foubert, P., De Schryver, F. C., Schoonheydt, R. A.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 13.05.2003
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la026786r

Hybrid clay-organic monolayers prepared using the Langmuir−Blodgett (LB) method are examined by polarized infrared attenuated total reflection spectroscopy (ATR), polarized grazing angle infrared reflection absorption spectroscopy (IRRAS), and atomic force microscopy (AFM). These spectra represent the first reported IR spectra of clay monolayers functionalized with cationic surfactants. The intensities of the ν(Si−O) bands of SapCa-1 saponite and SWy-1 montmorillonite on both Ge and ZnSe substrates were analyzed quantitatively using the thin film approximation. The measured intensity on both substrates corresponds to the calculated intensity of one clay layer (0.96 nm), indicating that a monolayer of clay was formed on ZnSe as well as on Ge. In the case of saponite, a trioctahedral smectite, the ν(OH) band at 3680 cm-1 and the out-of-plane ν(Si−O) band at 1063 cm-1 show dichroic ratios of 0.33 and 0.23, respectively, consistent with the nearly perpendicular orientation of these bonds in the film. For SWy-1, a dioctahedral smectite, the ν(OH) bands have a dichroic ratio of slightly higher than 1.0, indicating that the structural OH groups are oriented more within the 001 plane. The dichroic ratios of the δ(OH) bands (AlAlOH, FeAlOH, and MgAlOH bending) show small differences representing subtle changes in mutual orientation of the hydroxyl groups. Similar to saponite, the out-of-plane ν(Si−O) of SWy-1 is highly oriented with a dichroic ratio of 0.12. Infrared reflection absorption spectra show even more pronounced dichroic ratios of the ν(Si−O) bands. From the polarized IR spectra and AFM, it has been confirmed that the clay particles are highly oriented in the LB monolayer.