Microscale mobile surface double layer in a glassy polymer.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 36351025.
- Also identified by DOI 10.1126/sciadv.abq5295 and PMC identifier 9645724.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
This study examines the origin of the widely different length scales, <i>h</i><sub>t</sub>-nanometers to micrometers-that have been observed for the propagation of the near-surface enhanced mobility in glassy polymers. Mechanical relaxations of polystyrene films with thicknesses, <i>h</i>, from 5 nm to 186 μm have been studied. For <i>h</i> < ~1 μm, the films relaxed faster than the bulk and the relaxation time decreased with decreasing <i>h</i> below ~100 nm, consistent with the enhanced dynamics originating from a near-surface nanolayer. For <i>h</i> > ~1 μm, a bulk-like relaxation mode emerged, while the fast mode changed to one that extended over ~1 μm from the free surface. These findings evidence that the mobile surface region is inhomogeneous, comprising a nanoscale outer layer and a slower microscale sublayer that relax by different mechanisms. Consequently, measurements probing the enhanced mobility of different mechanisms may find vastly different <i>h</i><sub>t</sub>'s as shown by the literature.