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
作者:
Jinlong Cheng,
Alexander Xenopoulos,
Bernhard Wunderlich,
期刊:
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals
(Taylor Available online 1992)
卷期:
Volume 220,
issue 1
页码: 127-157
ISSN:1058-725X
年代: 1992
DOI:10.1080/10587259208033435
出版商: Taylor & Francis Group
关键词: tetra-n-alkylammonium bromides and iodides;disorder and motion;plastic crystal;condis crystal;solid state13C NMR;thermal analysis
数据来源: Taylor
摘要:
Disorder and motion in crystals and mesophases of tetra-n-alkylammonium halides of intermediate chain length alkyl groups, [CH3(CH2)n-1]4NX, wheren= 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 state13C 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.
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