Conformation of Surfactant Molecules in the Interlayer of Montmorillonite Studied by ¹³C MAS NMR

Abstract

The ordering conformation of surfactant molecules in intercalated montmorillonite prepared at various concentrations was investigated by 13C MAS NMR. The 13C MAS NMR study demonstrates the coexistence of ordered and disordered chain conformations. Two main resonance peaks are associated with the backbone alkyl chains: the resonance at 33 ppm corresponds to the ordered conformation (all-trans), and the resonance at 30 ppm corresponds to the disordered conformation (mixture of trans and gauche). Deconvolution of 13C MAS NMR spectra indicates that the ordering conformation of surfactant molecules within the gallery of montmorillonite depends very much on their orientation and packing density. When amine chains are oriented parallel to the silicate layers, the amount of all-trans conformer decreases with the increase of amine concentration. However, the amount of all-trans conformer increases with the increase of amine concentration when amine chains radiate from the silicate layers. Furthermore, 13C MAS NMR spectra show that the intercalated surfactant molecules in the clay minerals never attained the complete liquidlike or solidlike behavior.

Silylation of montmorillonite surfaces: Dependence on solvent nature

“…For pristine Mt, the basal spacing increased with the increase in the intercalated surfactant amount (Fig. 4a), similar to those reported in the literature [9,30]. When the CTAB concentration increased to 2.0 CEC, the maximum basal spacing reached 3.74 nm.…”

Locking effect: A novel insight in the silylation of montmorillonite surfaces

“…The new reflection at around 8.2 (2q) (Fig. 1eeh) is attributed to the (002) reflection of the silylated product, similar to those of the cationic surfactant modified Mts [9]. The d 001 value remains unchanged after a further CTAB intercalation as the concentration reaches 2.0 CEC, whereas the basal spacing of the only surfactant intercalated Mt increases to 3.74 nm.…”

The influence of alkyl chain length on surfactant distribution within organo-montmorillonites and their thermal stability

“…Various structural models of organoclays have been proposed by using experimental technologies (e.g. XRD, FTIR, NMR, and TEM) [8][9][10][11][12][13][14] and molecular modelling methods [15][16][17]. And their thermal stabilities have been examined by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) [13,[18][19][20][21][22][23][24][25], TGA combined with infrared spectroscopy and mass spectrometry (TGA-FTIR-MS) [26,27], and TGA combined with pyrolysis/ GC-MS [28].…”