Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR

The molecular conformation and mobility of the intercalated surfactant molecules, cetyltrimethylammonium bromide (CTMAB), have been studied using Fourier transform IR spectroscopy (FTIR) and high-resolution single-pulse 13C magic-angle-spinning nuclear-magnetic-resonance (13C SP MAS NMR) spectroscopy. Conformation and mobility of alkyl chains was found to be a function of the surfactant concentration. The splitting of the methylene scissoring mode at 1473-1463 cm-1 and the rocking mode at 730-720 cm-1 in FTIR is considered to be diagnostic of the packing density increase of the intercalated surfactants within the clay gallery. Compare with the 13C SP MAS NMR spectrum of CTMAB in the bulk state, 1~ 3 ppm upfield chemical shifts for end-methyl (δC16) and methylene (δC15, δC2-14) of the intercalated surfactant molecules in the hybrids indicate the more free conformational situation. For these hybrids, the conformational freedom decrease with the increase of surfactant concentration. In addition, ~2 ppm downfield shift for the C1 carbon atom in the hybrids with higher surfactant content suggests a special local environment. This study demonstrates the different mobility of carbon atoms in the intercalated alkyl chain