title: Symmetric C-C stretching mode splitting versus CH2-chain conformation order in sodium montmorillonite modified by cetyltrimethylammonium bromide.
abstract: 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(2)-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 CH(2)-chain of the alkylammonium ion embedded into the clay interlayer space. We report Raman experimental evidence for a CH(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(2)-chain bending provides a general understanding of conformation reorganization and switching within long CH(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(1295)(CH(2))/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.
authors.affiliation: AM Prokhorov General Physics Institute of Russian Academy of Sciences, Moscow, Russia. sagitova@kapella.gpi.ru
authors.forename: Elena A
authors.initials: EA
authors.lastname: Sagitova
authors.forename: Patrice
authors.initials: P
authors.lastname: Donfack
authors.forename: Kirill A
authors.initials: KA
authors.lastname: Prokhorov
authors.forename: Goulnara Yu
authors.initials: GY
authors.lastname: Nikolaeva
authors.forename: Viktor A
authors.initials: VA
authors.lastname: Gerasin
authors.forename: Nadezhda D
authors.initials: ND
authors.lastname: Merekalova
authors.forename: Arnulf
authors.initials: A
authors.lastname: Materny
authors.forename: Evgeny M
authors.initials: EM
authors.lastname: Antipov
authors.forename: Pavel P
authors.initials: PP
authors.lastname: Pashinin
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D001546:Bentonite / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002244:Carbon / Q000737:chemistry; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D000077215:Clay; D053761:Nanocomposites / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D002593:Cetrimonium Compounds; D001546:Bentonite; D002244:Carbon; D000077215:Clay; D000077286:Cetrimonium