Showing papers by "Jianxi Zhu published in 2004"
TL;DR: In this paper, the ordering conformation of surfactant molecules in intercalated montmorillonite prepared at various concentrations was investigated by C-13 MAS NMR, which demonstrates the coexistence of ordered and disordered chain conformations.
Abstract: The ordering conformation of surfactant molecules in intercalated montmorillonite prepared at various concentrations was investigated by C-13 MAS NMR. The C-13 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). Deconvolution of C-13 MAS NMR spectra indicates that the ordering conformation of surfactant molecules within the gallery of montmorillonite depends very much on their orientation and packing density. When amine chains are oriented 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, C-13 MAS NMR spectra show that the intercalated surfactant molecules in the clay minerals never attained the complete liquidlike or solidlike behavior.
98 citations
TL;DR: Mullites synthesized from four kaolinites with different random defect densities have been studied by 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy and X-ray diffraction and it is revealed that the mullites derived from kaolinite with high defect density, have a sillimanite-type Al/Si ordering scheme and are low in silica.
65 citations
TL;DR: A Raman spectroscopic study on organo-montmorillonites prepared at different concentrations provided detailed observations about the ordering conformation of HDTMA+ ions confined within the montmorillonite interlayer as discussed by the authors.
Abstract: A Raman spectroscopic study on the organo-montmorillonites prepared at different concentrations provided detailed observations about the ordering conformation of HDTMA+ ions confined within the montmorillonite interlayer. The ordering conformation shows a strong dependence on the concentration of the confined amine. Both the wavenumber and bandwidth of antisymmetric and symmetric stretching modes are sensitive to the ordering conformation of the inserted organic cation. Furthermore, the wavenumber of the antisymmetric stretching mode is more sensitive than that of the symmetric stretching mode to the mobility of the tail of the amine chain. At room temperature, the conformational ordering is more easily affected by the packing density in the lateral model than in the paraffin-type model. However, at liquid nitrogen temperature, both the positions of antisymmetric and symmetric stretching modes are independent of the amine concentration, and the bandwidth of symmetric stretching mode is sensitive to the organic ordering conformation. Upon heating the organo-montmorillonites, the positions of both the antisymmetric and symmetric stretching bands shift to higher wavenumbers, indicating a decrease of conformational ordering. Copyright © 2004 John Wiley & Sons, Ltd.
37 citations