Ionic dynamics in the rotator phase of n-alkylammonium chlorides (C6–C10), studied by 1H nuclear magnetic resonance, electrical conductivity and thermal measurements

Abstract

¹ H NMR, electrical conductivity and thermal measurements have been performed on the rotator phase of n-alkylammonium chlorides C_nH_2n+1 NH₃Cl (n= 6–10). Rapid two-dimensional self-diffusion and uniaxial rotation of the long rod-like cations were observed in all salts studied by measuring ¹H NMR spin–lattice relaxation times T₁ and T_1ρ, indicating the highly disordered structure of the rotator phase. Marked ionic self-diffusion was detected in this phase by measuring a.c. electrical conductivity which increased to ca. 10^–2 S m^–1 near the respective melting temperatures. Analysing the NMR relaxation and conductivity data, it was found that the anions also diffuse in this phase to a similar extent to the cations. From the characteristic dynamic behaviour in this phase, together with the small melting entropies (<20 J K^–1 mol^–1) reported, the rotator phase can be considered to be a low-dimensional plastic crystal or an intermediate state between the plastic crystal and smectic liquid crystal.