Low temperature aging in a molecular glass: the case of cis-methyl formate. Issue 29 (19th July 2021)

• Record Type: Journal Article
• Authors: Cassidy, Andrew; Jørgensen, Mads R. V.; Glavic, Artur; Lauter, Valeria; Plekan, Oksana; Field, David
• Is Part Of: Physical chemistry chemical physics. Volume 23:Issue 29(2021)
• Page Start: 15719
• Page End: 15726
• Publication Date: 2021-07-19
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp01332g
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The spontaneously generated electric field in a molecular glass, decays with time at deeply supercooled temperatures. Here, we fit the rate of decay with a model to extract the activation barrier to molecular rotation, as the glass ages. Abstract : Glassy films of cis -methyl formate show spontaneous dipole orientation on deposition from the vacuum, the so-called 'spontelectric effect', creating surface potentials and electric fields within the films. We follow the decay of these fields, and their accompanying dipole orientation, on the hours timescale at deposition temperatures between 40 K and 55 K. Our data trace the low temperature 'secondary decay' mechanism, at tens of degrees below the glass transition temperature of 90 K. We show that secondary decay is due to molecular rotation, with associated activation energies lying between 0.1 and 0.2 eV. Diffusion is absent, as established from published neutron reflectivity data. Using an analytical model for the spontelectric effect, data are placed on a quantitative footing, showing that angular motion in excess of 50° reproduces the observed values of activation energies. Exploitation of the spontelectric effect is new in the study of glass aging and is shown here to give insight into the elusive processes which take place far from the molecular glass transition temperature.