Symmetric C–C Stretching Mode Splitting versus CH2-Chain Conformation Order in Sodium Montmorillonite Modified by Cetyltrimethylammonium Bromide

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 CH2-chain’s symmetric C–C stretching Raman mode found at ∼1128 cm–1 in cetyltrimethylammonium bromide i...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2012-01, Vol.116 (1), p.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:
Aluminum Silicates - chemistry
B: Surfactants, Membranes
Bentonite - chemistry
Calorimetry, Differential Scanning
Carbon - chemistry
Cetrimonium Compounds - chemistry
Nanocomposites - chemistry
Spectrum Analysis, Raman
X-Ray Diffraction
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Summary: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 CH2-chain’s symmetric C–C stretching Raman mode found at ∼1128 cm–1 in cetyltrimethylammonium bromide into two bands at 1128 and 1139 cm–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 CH2-chain of the alkylammonium ion embedded into the clay interlayer space. We report Raman experimental evidence for a CH2-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 CH2-chain bending provides a general understanding of conformation reorganization and switching within long CH2-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 1295(CH2)/I 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.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp208036c