Rotator Phase in Dodecylammonium Chloride Studied by 1H and 2H Solid NMR and Thermal Measurements

Abstract

Abstract 1H NMR spin-lattice relaxation times, T1 and T1ρ, the second moment M2 of 1H NMR linewidth, 2H NMR spectra, powder X-ray diffraction, electrical conductivity, and thermal measurements have been performed on C12H25NH3Cl and C12H25ND3Cl in the range between room temperature and the melting point. From these measurements, the presence of the rotator phase was revealed above ca. 345 K, where a highly disordered structure characterized by the rapid 2-D self-diffusion as well as the axial rotation of the cations taking place in the lamellar-type double layer structure is formed. These molecular motions, the crystal structure and the thermal nature found in this phase indicate that the rotator phase is close to the plastic crystal and can be described as “a low-dimensional plastic phase”. The determined dynamic parameters of molecular motions in this phase were compared with those in the values reported in the rotator phases of short alkyl chain analogues.