Glycerol confined in zeolitic imidazolate frameworks: The temperature-dependent cooperativity length scale of glassy freezing

M Uhl; J K H Fischer; P Sippel; H Bunzen; P Lunkenheimer; D Volkmer; A Loidl

doi:10.1063/1.5080334

Glycerol confined in zeolitic imidazolate frameworks: The temperature-dependent cooperativity length scale of glassy freezing

J Chem Phys. 2019 Jan 14;150(2):024504. doi: 10.1063/1.5080334.

Authors

M Uhl¹, J K H Fischer¹, P Sippel¹, H Bunzen², P Lunkenheimer¹, D Volkmer², A Loidl¹

Affiliations

¹ Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany.
² Chair of Solid State and Materials Chemistry, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany.

PMID: 30646699
DOI: 10.1063/1.5080334

Abstract

In the present work, we employ broadband dielectric spectroscopy to study the molecular dynamics of the prototypical glass former glycerol confined in two microporous zeolitic imidazolate frameworks (ZIF-8 and ZIF-11) with well-defined pore diameters of 1.16 and 1.46 nm, respectively. The spectra reveal information on the modified α relaxation of the confined supercooled liquid, whose temperature dependence exhibits clear deviations from the typical super-Arrhenius temperature dependence of the bulk material, depending on the temperature and pore size. This allows assigning well-defined cooperativity length scales of molecular motion to certain temperatures above the glass transition. We relate these and previous results on glycerol confined in other host systems to the temperature-dependent length scale deduced from nonlinear dielectric measurements. The combined experimental data can be consistently described by a critical divergence of this correlation length as expected within theoretical approaches assuming that the glass transition is due to an underlying phase transition.