XRD and NMR characterization of synthetic hectorites and the corresponding surfactant-exchanged clays
Abstract:Synthetic hectorites and the corresponding surfactant-exchanged clays have been characterized by X-ray diffraction and 1H, 7Li, 13C, 23Na and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. The low-charge clays retain water more efficiently, forming aggregates without extensive drying. The hydroxylated hectorite exhibits two 1H NMR signals near 0 ppm whereas the fluorohectorites are characterized by a single peak in the same region. The 23Na 2D 3Q magic angle spinning (MAS) spectra of the low-charge hectorites show a single peak. The 29Si NMR shift depends on the interlayer charge. Tactoids formed by the low-charge hectorites reduce the rate of surfactant incorporation. The population of the all-trans conformer of the hydrocarbon chain, determined by 13C MASNMR, varies with the surfactant content. 13C NMR relaxation data show an increase in mobility with the surfactant loading and along the long alkyl chain, from the polar head to the terminal group. Complexity of the motional behaviour precludes any detailed analysis. These modified clays are not useful in preparing poly (-caprolactone) nanocomposites by in situ polymerization.
Document Type: Research Article
Publication date: June 1, 2008