Phase behaviour and relaxation dynamics of the asymmetric azoxybenzene

Abstract

ABSTRACT The phase behaviour and molecular dynamics of the liquid crystal 4-decyl-4’-heptylazoxybenzene (abbreviated as 10AB7) are described by differential scanning calorimetry, polarized optical microscopy, X-ray diffraction and broadband dielectric spectroscopy. Upon fast cooling/heating rates, the 10AB7 forms two liquid crystal phases, nematic and smectic A, as well as two conformationally disordered crystal phases (one of them does not appear on cooling). Upon slow cooling, there is the multiplicity of crystal phases. The dielectric spectra reveal the complex dynamics in the individual thermodynamic states of 10AB7. The Arrhenius type high-frequency relaxation, related with the rotations around the long axes of molecules, is detected for each liquid-like phases and for the high-temperature crystal phase. In the crystal phases there is also the Arrhenius type relaxation associated with the collective motions of molecules combined due to the mutual interactions through NO molecular groups. Additionally, the Vogel–Fulcher–Tammann type process is visible in the low-temperature crystal phase. GRAPHICAL ABSTRACT