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.
| Original language | English |
|---|---|
| Pages (from-to) | 15719-15726 |
| Number of pages | 8 |
| Journal | Physical Chemistry Chemical Physics |
| Volume | 23 |
| Issue number | 29 |
| DOIs | |
| State | Published - Aug 7 2021 |
Funding
AC and MRVJ are grateful for the support of the Danish National Research Foundation (Center for Interstellar Catalysis, DNRF150 and Center for Materials Crystallography, DNRF93 respectively). We thank the Danish Agency for Science, Technology and Innovation for funding the instrument centre DanScatt. This research is supported by the experiment that used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.