Characterization of the structure of modified clay by Raman spectroscopy

Abstract

One of promising fillers for polymers, sodium montmorillonite modified by dioctadecyldimethylammonium bromide (DODAB), has been studied by Raman spectroscopy, X-ray analysis, and differential scanning calorimetry (DSC). It has been shown that an increase in the DODAB content enlarges the height of a clay interlayer space through filling the clay interlayer galleries with DODAB molecules. According to both Raman and DSC data, DODAB molecules grafted to the clay can be in three different phase states depending on the modifier content. At a low DODAB content, its molecules are separated and contain a significant amount of gauche-conformers in methylene chains. At a medium content, the DODAB molecules form clusters, and the amount of trans-conformers in the DODAB methylene chains considerably increases. At a high DODAB content, its molecules are straightened and form a 2D ordered structure with either hexagonal or triclinic symmetry.Computer-simulated schematic structure of the interlayer space of Na + -montmorillonite modified by DODAB

Thermal stability and hot-stage Raman spectroscopic study of Ca-montmorillonite modified with different surfactants: A comparative study

“…Moreover, the symmetric C H stretching band is very close to the wavenumber of the pure surfactants in addition to a slight shift to high wavenumber at relatively lower concentration and shows no obvious dependence on the concentration of amine. By comparison with the previous studies by He et al and Prokhorov et al [11,12], similar variation trends were obtained. On the other hand, as for CTAB, the intensity of asymmetric C H stretching vibration is higher than that of the other two surfactants with shorter chain length.…”

“…It is clear that the loading amounts of surfactants affect the position of the asymmetric stretching vibration of methylene groups, which is in line with the previous studies [11]. In the high concentration range (1.0-2.0 CEC), the position of the asymmetric stretching vibration of methylene groups keep relatively constant, while the position of the asymmetric C H stretching band shifts to the higher wavenumber, which is directly connected with the increase in the amount of gauche-conformers and the disordering of molecular packing [12,13,26,27]. Based on XRD results, 1.0 CEC is the critical concentration for the change of the structure of the organophillic layer, which is also the point where the dramatic wavenumber shift ends and begins to keep relatively constant.…”

“…This is attributed to the fact that the molecular environment for surfactants confined within the montmorillonite gallery is different from that for pure crystalline surfactants and maybe because the CH 2 units bond to the siloxane surface and/or to the hydroxyl surface [11,12]. It is clear that the loading amounts of surfactants affect the position of the asymmetric stretching vibration of methylene groups, which is in line with the previous studies [11].…”

“…To the best of our known, there are only limited Raman investigations so far focused on the confined molecules in organo-montmorillonites [11][12][13]. Moreover, most of organomontmorillonites were prepared by Na-montmorillonites, while only few previous studies provided insights into the synthesis and characterization of Ca-montmorillonites modified by different surfactants [1,4,5,[14][15][16].…”

Computational Studies of Ionic Liquids

“…The increased adsorption of perchlorate with increasing d-spacing is attributed to the enhanced access of perchlorate ions on to the clay surface. Raman spectroscopy was used for conformational analysis to account for the decreased d-spacing on adsorption by measuring the intensity of symmetric (2847 cm -1 ) and asymmetric (2878 cm -1 ) stretching vibrations of methylene groups present [Prokhorov et al 2005]. Trans conformer shows higher intensity for asymmetric stretching than symmetric stretching and in gauche conformer symmetric stretching is reported to possess higher intensity.…”