Mesophases of Alkylammonium Salts III. Disorder and Motion in the Intermediate Homologs: [CH3(CH2)n-1]4NX,n= 4, 5, 6, 7 and X = Br and I

Abstract

Abstract Disorder and motion in crystals and mesophases of tetra-n-alkylammonium halides of intermediate chain length alkyl groups, [CH3(CH2) n-1]4NX, where n = 4, 5, 6, 7 and X = Br and I, have been analyzed based on entropy changes of phase transitions known from differential scanning calorimetry (DSC) and new measurements of solid state 13C nuclear magnetic resonance spectra (NMR). Some mesophase transitions from the crystal state involve only conformational motion and disordering to lead to condis crystals. The conformational motion and disordering in the alkyl chains may also be introduced gradually (transitionless change to a condis crystals). Further heating of the samples increases the degree of conformational disorder (entropy) to reach different, more disordered condis states, or causes orientational motion and disorder of the cation as a whole to form plastic crystals, which in this intermediate alkyl chain-length group of salts contain always conformational disorder. Finally, isotropization occurs either directly from the condis state or out of the plastic crystal.