Symmetric C-C Stretching Mode Splitting versus CH sub(2)-Chain Conformation Order in Sodium Montmorillonite Modified by Cetyltrimethylammonium Bromide

• Published in: The journal of physical chemistry. B 2012-01, Vol.116 (1), p.221-231-221-231
• Main Authors: Sagitova, Elena A, Donfack, Patrice, Prokhorov, Kirill A, Nikolaeva, Goulnara Yu, Gerasin, Viktor A, Merekalova, Nadezhda D, Materny, Arnulf, Antipov, Evgeny M, Pashinin, Pavel P
• Format: Article
• Language: English
• Subjects: Carbon-carbon composites; Cetyltrimethylammonium bromide; Clay (material); Galleries; Interlayers; Splitting; Stretching; Symmetry
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp208036c

Exploiting Raman spectroscopy and computational modeling, for the first time, we report and explain an interesting phenomenon in clay modified by cetyltrimethylammonium bromide. A splitting of the CH sub(2)-chain's symmetric C-C stretching Raman mode found at 1128 cm super(-1) in cetyltrimethylammonium bromide into two bands at 1128 and 1139 cm super(-1) in clay modified by cetyltrimethylammonium bromide is observed. We demonstrate that this splitting appears if two types of trans-segments with nonequivalent lengths and terminal groups coexist in the CH sub(2)-chain of the alkylammonium ion embedded into the clay interlayer space. We report Raman experimental evidence for a CH sub(2)-chain bending within the clay galleries, resulting in the symmetric C-C stretching band splitting, as was also suggested by computational modeling. Noteworthy, we postulate that this unique behavior based on CH sub(2)-chain bending provides a general understanding of conformation reorganization and switching within long CH sub(2)-chain molecules confined within modified clay interlayer galleries. For all modifier concentrations, we show that the intercalated cetyltrimethylammonium ions exist in a liquid-like state, consisting mainly of trans conformations (86%) of two types in approximately equal proportions. Moreover, we demonstrate that the integral Raman intensity ratio I sub(1295)(CH sub(2))/I sub(705)(clay) provides a rapid nondestructive quantification of the relative content of alkylammonium ions in modified clays. These results demonstrate that a simple direct monitoring of specific modifier-dependent interlayer conformational states is possible, which is of great importance for a tunable fabrication of modified clays-based nanocomposites with desired properties.