Conformation Heterogeneity and Mobility of Surfactant Molecules in Intercalated Clay Minerals Studied by Solid-State NMR

Abstract

The conformation heterogeneity and mobility of surfactant molecules in intercalated montmorillonite clay minerals have been investigated using variable-temperature solid-state 13C NMR and two-dimensional proton wide-line separation (2D WISE) 1H−13C NMR spectroscopy. Previous FTIR studies by Vaia et al. for the first time revealed the existence of a gauche conformation of surfactant molecules in clay minerals and further illustrated the transition from an ordered conformation, to a liquid crystalline state, to completely liquidlike behavior. The NMR study reported in this paper clearly demonstrates the coexistence of order and disordered chain conformations. Two main resonance peaks are resolved and 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). The NMR technique allows detailed characterization and quantification of the conformation...