Dielectric relaxations in a supercooled liquid and glassy smectic phase

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Abstract
The real and imaginary parts of the complex dielectricpermittivity of the supercooled smecticG phase of N‐(4′‐n‐pentyloxybenzylidene)‐4‐n‐butylaniline have been measured from 50 Hz to 200 kHz and 77 to 260 K. The glass transitiontemperature of the smectic phase is 181 K. Two relaxation regions were observed; one above and the second below T g , designated as α and β relaxations, respectively. The half‐width of the spectrum for both relaxations increases on cooling. The rate of α relaxation follows the Vogel–Fulcher–Tamman equation, but that of β relaxation an Arrhenius equation with an activation energy of 14 kJ mol− 1. The increase in static dielectricpermittivity on cooling is consistent with Curie law and indicates no change in the orientational correlation with temperature. The dielectric relaxation in the smectic phase is similar to that observed in amorphous polymers, rigid molecular glasses, nematic and cholesteric glasses, and the glasslike state of orientationally disordered crystals. This suggests that the molecular mechanism of relaxations in the glassy state is less dependent upon the presence of internal degrees of freedom of molecules or the degree of order in their arrangement than is generally considered.