Phase behaviour and dynamics of the liquid crystal 4-ethyl-4′-octylazoxybenzene (4EOB)

The results of Broadband Dielectric Spectroscopy and Differential Scanning Calorimetry of the 4-ethyl-4 '-octylazoxybenzene (4EOB) liquid crystal are presented. Numerical analysis of the dielectric spectra results points to complex dynamics of the liquid crystal molecules in isotropic liquid, nematic and conformationally disordered crystalline phases. Two well-separated maxima on the imaginary part of electric permittivity were detected and described in liquid-like and crystalline phases. A third relaxation process, hidden in the conductivity region, describing conformational disorder of alkyl chains has been found in some plastic crystal phases. Temperature dependences of mean relaxation times characterising conformational disorder, flip-flop motions and rotation around long axis are of the Arrhenius type in liquid-like phases and conformationally disordered crystalline phases, and of the Vogel-Fulcher-Tammann type in the low-temperature crystalline phases for relaxation processes around short and long axis.