Fig xA C MAS NMR spectra of
Loading of HDTMA+ to the montmorillonite induced changes in the relative intensities of the resonances. The AS1404 signal in the spectra was that assigned to carbons of the –CH2– groups from alkyl chains (at 1.3 ppm), overtaking of the signal at δ = 3.5 ppm in intensity ( Fig. 4C-a). Changes in the intensities of signals could be ascribed to the superposition of two resonances with similar chemical shift: hydrogens from structural OH groups of montmorillonite (1.6 ppm) and hydrogens from methylene groups of alkyl chains (1.3 ppm). One more factor may influence the intensity of the signals. The mobility of the alkyl chains increased after loading compared to their mobility in the rigid structure of the HDTMA-Br salt. Greater mobility led to the narrowing of the signal width of methylene groups –CH2– in alkyl chains. In contrast, the mobility of the carbons from CH3–N–, CH2–N– (signal at 3.6 ppm) remained low due to strong electrostatic bonding of the head-group to the montmorillonite layer in the vicinity of the negative layer charge. Consequently, the resolution of the –CH2– signal was improved in the spectra compared to the resolution in the spectrum of HDTMA-Br ( Fig. 4 insert-b).