Thermal & Dielectric Spectroscopic Investigation on Orientationaly Disordered Crystal- Cyclobutanol

Abstract

Abstract Orientationallydisordered crystals (plastic crystals) maintain translational order along their crystallographic axis while continue to have orientational degrees of freedom. Since freezing of orientational motion of molecule leads to glass transition, these rotationally disordered systems form glassy crystals below their glass transition temperature. Because of the presence of translational order, these kind of materials can easily treated in both mathematical and simulation approaches and are considered as the ideal or model system for studying glass transition phenomena. Here by using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), thermal and dielectric behaviour of the orientation ally disordered phases of an organic plastic crystal cyclobutanol have been studied. During quench cooling of the sample below the melting point, three solid-solid phase transitions, one at 180K called phase I, other at 170K called phase II, and another one at 158 K and glass transition (133K) events were observed using the DSC. The dielectric spectra of the cyclobutanol were recorded in a wide frequency range of 10-2 Hz to 107Hz for different temperatures. The dielectric spectra revealed the presence of the three phases, of which phase I was observed below the melting point up to nearly 180 K, the phase II was observed up to nearly 170 K and phase III was observed further up to 158K. In these phases signatures of two structural α relaxations were observed. The secondary relaxation below the glass transition event was also seen, whose strength was found to be very small compared to those observed in other plastic crystals. The α relaxation showed non-Arrhenius temperature dependence depicted by Vogel-Fulcher-Tammann equation,while secondary relaxation mimicked Arrhenius temperature dependence.