Thermotropic Mesophases of the C₈, C₁₀, C₁₂and C₁₆n-Alkyl Ammonium Chlorides

Liquid crystalline and solid phases of the title compounds were studied by optical microscopy, differential scanning calorimetry and X-rays. Transition temperatures, heats and layer spacing were determined. In all the compounds the isotropic liquid is preceded by a neat (bilayer smectic A) phase, which in turn is preceded hy an intermediate phase which is separated from the room temperature crystalline phase phase by 2 to 4 first order phase transition. The intermediate phase has a structure consisting of disordered hydrocarbon chains held in place by their ionic heads (-NH3 +), with the chains perpendicular to the ionic layers. This phase which is shown to be uniaxial by convergent light observations, may be best described as also being a liquid crystal.