DSC and X-ray diffraction study of polymorphism in n-alkylammonium chlorides

The influence of the hydrocarbon chain length in the formation of interdigitated and non-interdigitated bilayers in n-alkylammonium chlorides has been investigated for chain lengths varying between 8 and 14 carbon atoms. The formation of non-interdigitated bilayers during crystallization from solution is favoured for shorter chains whilst the interdigitated structure is predominant for larger chains. The thermodynamic parameters of the solid to solid phase transitions in the non-interdigitated samples depend on chain length showing the odd-even alternation that characterized homologous series in n-paraffins. The solid to liquid crystal phase transition temperatures and enthalpies show a linear dependence with the chain length.