The Phase Transition of 1-Alkyl-4-aza-1-azoniabicyclo[2.2.2]octane Bromides, Cn-DABCO-Br (11≤n≤22)

Abstract

Abstract The phase transitions of a series of 1-alkyl-4-aza-1-azoniabicyclo[2.2.2]octane bromides were studied on the basis of DSC, measurements of the ionic conductivities of the bromide anion, and Raman spectroscopy. Two endothermic signals were observed at the temperatures of Tc1 and Tc2(Tc1<Tc2) for most of the materials. The transition enthalpies and transition entropies were not very different for the transitions at Tc1, irrespective of the alkyl-chain lengths attached to DABCO nitrogens. On the other hand, these values tended to increase with an increase in the alkyl-chain lengths for the transitions at Tc2. The temperature dependences of the ionic conductivities of the bromide anion showed abrupt increases in the conductivities by a factor of 2–10. The conductivity jumps were observed around Tc2. The temperature dependences of the Raman spectra gave detailed information on the phase transition; (1) the change in the subcell structure took place at Tc1, with the concomitant occurrence of a conformational change in the alkyl group; (2) above Tc2, the alkyl chain takes a liquid-like disordered form, and a rotational motion of the DABCO portion sets in.