Molecular dynamics of 4-propyl-4′-thiocyanatobiphenyl (3BT) in the strong glass-forming smectic E phase

Broadband dielectric spectroscopy was employed to study glass transition dynamics in highly ordered smectic E phase of 4-propyl-4′-thiocyanato-1,1′-biphenyl (3BT). Three relaxation processes exhibiting Arrhenius-like thermal activation were detected: (1) δ-relaxation assigned to molecular reorientation around the short axis, (2) α-relaxation attributed to rigid molecular cores tumbling around the long axis and (3) secondary β-relaxation. Our investigations revealed that the smectic E phase (SmE) is a strong glass-former with the smallest possible fragility index mf ~ 16. Finally, an analysis of loss spectra (ε″(f)) in terms of their shape parameters (1 − m) and n demonstrated long and short range coupling between molecular motions in the glassy state.