NMR Study of Slow Motions of HDA Hydrocarbons Chains Inside Lamellar Structures

Abstract

Measurements of ¹H and ¹³C Nuclear Magnetic Resonance (NMR) for the nanocomposite materials formed by the intercalation of hexadecylamine (HDA) in metal oxides (TiO₂, V₂O₅ and MoO₃), are reported. The ¹H NMR spin-lattice relaxation in the rotating frame was described by using the spectral density due to Davidson and Cole, which incorporates a distribution of correlation times characterized by a width parameter ϵ. The fitting of the data was obtained for ϵ = 0.74, indicating that the correlation times are distributed over a narrow range in this system. High-resolution ¹³C NMR techniques were used to resolve the NMR lines of middle-chain methylene groups in the spectra and variable contact time cross-polarization {¹H-}¹³C experiments were employed to analyze the reorientation dynamics of the CH₃ and CH₂ groups in the HDA chains.

Keywords:

• foam
• hexadecylamine
• intercalation compound
• nanostructure
• NMR

Acknowledgments

Partial support of Capes, CNPq, FAPESP and PRONEX /FAPESP / CNPq (Grant 03/09859-2) and FONDECYT (Grants 105344 and 7070308) are gratefully acknowledged.