An Investigation of Smectic A—Nematic and Nematic—Isotropic Phase Transitions

The phases and phase transitions in two homologues of the 4‐(4′‐n‐alkyloxy‐benzoyloxy) benzylidene‐2″‐methylaniline (decyloxy and dodecyloxy) are characterized using a variety of experimental techniques. These are differential scanning calorimetry, thermal microscopy, X‐ray diffraction, ESR spectroscopy, and density determination. The nematic—isotropic transition is found to be of first order but with a smaller transition entropy, in both of the compounds, than expected. The smectic A—nematic transition is found to be of weak first order in both of the compounds. The experimental results are compared to those of other compounds which have comparable molecular lengths and with the predictions of a molecular field theory of smectic A liquid crystals.