On the features of the dielectric response of supercooled ethylcyclohexane

Abstract

The main relaxation observed in supercooled ethylcyclohexane in the 50 Hz–20 kHz frequency range using high-resolution dielectric spectroscopy displays an unusual relaxation pattern. The slope of the dielectric loss profile above the peak frequency, progressively tends to zero with increasing temperature. The observed features could be compatible with the existence of different underlying processes. A simple approach based on scaling is exploited to provide relevant information on the properties of the primary and secondary relaxation in ethylcyclohexane. The apparently anomalous behaviour is shown to be due to the superposition of a secondary process to the dielectric α-process and support the thesis that the β-relaxation observed in the glassy phase could have an intramolecular origin.

Keywords:

• dielectric relaxation
• ethylcyclohexane
• secondary relaxations
• high resolution dielectric spectroscopy
• intramolecular processes
• Johari-Goldstein relaxation

Notes

1. Namely m ≅ 62 if calculated on the basis of the VFT parameters describing the temperature dependence of τ_max = 1/(2πν_peak), where the ν_peak values are those obtained for the construction of the master curve, but m ≅ 56 if calculated from the VFT parameters associated with the values of τ_max deduced from the best fit of the experimental spectra to a Havriliak-Negami equation as in Mandanici et al. [1].

2. The uncertainty on the values of the secondary peak frequency associated with β_KWW values in the range 0.51–0.55 is comparable with the size of the symbols representing these data in Figure 4. However, additional uncertainty might be due to the limited frequency range of the experimental data and to the master curve construction procedure as discussed in the text.