Influence of the hydrocarbon chain length in the phase transition from solid to liquid-crystal in n-alkylammonium chlorides

The influence of the hydrocarbon chain length in the solid to liquid-crystal phase transition in n-alkylammonium chlorides has been investigated for chain lengths varying between 8 and 14 carbon atoms. Both the temperature and the enthalpy of the transition show a linear dependence on the hydrocarbon chain length. Samples crystallized from the liquid-crystal phase, show thermal hysteresis and the solidification temperature is shifted down 4°C. The X-ray diffraction pattern of the liquid-crystal phase shows that the liquid crystal is smectic A2 type.