Orthogonal smectic phases in a biphenylyl chiral mesogen: Polarizing microscopy, synchrotron diffraction and dielectric spectroscopy studies

Abstract

Three orthogonal smectic phases (SmE*, SmB*hex and SmA*) have been identified in a biphenylyl chiral compound from optical polarizing microscopy, synchrotron X-ray diffraction and dielectric spectroscopy studies. SmB*hex phase exhibits two variants – the lower temperature one is more ordered. All the phases are found to be partially bi-layer type, observed first time in a chiral system without any cyano terminal group. Long range ordering is revealed in both the in-plane and across the plane correlations. Cell parameters of the herringbone like structures of higher ordered smectic phases have been determined and are found to be densely packed. Transitions from SmE* to SmB*hex and within the two SmB*hex variants are of displacive type. Dielectric spectroscopy reveals Maxwell Wagner relaxation in all the phases, however, flip-flop mode relaxation about molecular short axis has been observed in the higher ordered smectic phases only. Absence of short axis relaxation mode as well as soft mode in SmA* phase has been explained.