Conformation of Surfactant Molecules in the Interlayer of Montmorillonite Studied by 13C MAS NMR

The ordering conformation of surfactant molecules in intercalated montmorillonite prepared at various concentrations has been investigated by 13C MAS NMR. The 13C MAS NMR study demonstrates the coexistence of ordered and disordered chain conformations. Two main resonance peaks are associated with the backbone alkyl chains: the resonance at 33 ppm corresponds to the ordered conformation (all-trans), and the resonance at 30 ppm corresponds to the disordered conformation (mixture of trans and gauche). The deconvolution of 13C MAS NMR spectra indicates that the ordering conformation of surfactant molecules within the gallery of montmorillonite strongly depends on their orientation and packing density. When amine chains have orientation parallel to the silicate layers, the amount of all-trans conformer decreases with the increase of amine concentration. However, the amount of all-trans conformer increases with the increase of amine concentration when amine chains radiate from the silicate layers. Furthermore, 13C MAS NMR spectra show that the intercalated surfactant molecules in the clay minerals never attained the complete liquidlike or solidlike behaviour.