Probing the Debye Dielectric Relaxation in Supercooled Methanol

Xin Li,Zeming Chen,Yanqin Gao,Li-Min Wang,Wenkang Tu

doi:10.3389/fmats.2015.00041

Abstract

The explanation of the dielectric dynamics in methanol would offer knowledge of the Debye relaxation in supercooled monoalcohols. However, due to the fast crystallization, it is hard to attain the dynamics of pure methanol in the deeply supercooled region. In this paper we studied the dynamics of methanol - 2-ethyl-1-hexanol mixtures with methanol concentration up to 80 mol% using dielectric and calorimetric measurements. Two main relaxations are detected in the dielectric spectra of the mixtures, and the slower one generally reproduces the Debye relaxation features reported in earlier studies of other monoalcohols. The validity of the ideal mixing law is verified for the relaxation time of the slower dynamics in the mixtures. The results suggest that the Debye relaxation is present in the dielectric spectra of methanol. The temperature dependence of the Debye relaxation time is constructed for the supercooled methanol.

Highlights

Common to glass-forming monoalcohols is the extra Debye type relaxations in dielectric spectra, manifested by the slower dynamics than the structural (α-) relaxation, which associates with liquid viscosity and calorimetric glass transitions (Hassion and Cole, 1955; Dannhauser, 1968; Kudlik et al, 1997; Petong et al, 1999; Johari et al, 2001; Wang and Richert, 2004; Fragiadakis et al, 2010; Pawlus et al, 2010; Gainaru et al, 2011; Power et al, 2011)
Two relaxations are observed in the dielectric spectra of the methanol–2E1H mixtures at the methanol-rich and 2E1H-rich compositions
For the 2E1H-rich compositions, it can be concluded that the relaxation I is of the same nature as the Debye relaxation detected in pure 2E1H, since the Debye relaxation has been proven not to disappear in the diluted monoalcohols until a certain concentration (Wang et al, 2005; El Goresy and Böhmer, 2008)

Summary

Introduction

Common to glass-forming monoalcohols is the extra Debye type relaxations in dielectric spectra, manifested by the slower dynamics than the structural (α-) relaxation, which associates with liquid viscosity and calorimetric glass transitions (Hassion and Cole, 1955; Dannhauser, 1968; Kudlik et al, 1997; Petong et al, 1999; Johari et al, 2001; Wang and Richert, 2004; Fragiadakis et al, 2010; Pawlus et al, 2010; Gainaru et al, 2011; Power et al, 2011). We examine the dielectric behaviors in the glass-forming solutions of methanol mixed with 2-ethyl1-hexanol, a typical Debye liquid featured by the separated Debye and α-relaxations and high glass-forming ability (Murthy, 1996; Wang and Richert, 2004; Wang et al, 2005; Jakobsen et al, 2008; Fragiadakis et al, 2010; Bauer et al, 2013). The glass transition temperatures, Tg–cal, are determined by the onset temperatures of the heat capacity jumps from glasses to supercooled liquids

Results

Discussion

Conclusion