Raman spectroscopic study of organo-montmorillonites

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 (C) 2004 John Wiley Sons, Ltd.