Dielectric relaxation of alkyl chains in graphite oxide and n-alkylammonium halides

Abstract

The dynamic of n-alkylammonium halides and n-alkylammonium cations (n = 12, 14, 16, 18) intercalated in graphite oxide (GO) have been investigated with complex impedance spectroscopy. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, elemental analysis and thermogravimetry served to characterize the materials. The intercalated alkylammonium cations distributes as monolayers (when n = 12, 14 or 16) or bilayers (when n = 18), with their long axis parallel to GO layers, and with cations of headgroups bonded ionically to C-O- groups of GO; backbones of the confined molecules remain free. All halides and intercalation compounds suffer dielectric loss at low temperature. Arrhenius plots of the thermal dependence of the loss peaks, which are asymmetric, produce apparent activation energies that rise with increasing n. Ngai’s correlated-state model helps to correct for effects of dipole-dipole interaction, leading to virtually identical values for actual activation energy of 110 meV ± 5%; the values are also almost the same as the barrier energy for internal rotation in the alkyl macromolecule. We conclude that the relaxation of the alkylammonium cations arises not from C3 reorientation of the CH3 at its headgroup, but from small-angle wobbling around its major axis, an intrinsic motion.

Impedance Spectroscopic Study on Rotator and Disordered Phases in Trimethylammonium Chlorides

“…The homologous trimethylammonium chlorides are quaternary ammonium salts, each consisting of a hydrophilic chloride, and a hydrophobic carbanion with four methyl groups attached to some alkyl chain. As cationic surfactants, they are often used to modify layered materials such as hydrotalcite and graphite oxide by way of self-assembly. − They find widespread applications in biological control, micellar catalysis, and flotation. − …”