The role of intramolecular relaxations on the structure and stability of vapor-deposited glasses
Open Access
- 24 June 2022
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 156 (24), 244703
- https://doi.org/10.1063/5.0087600
Abstract
Stable glasses (SGs) are formed through surface-mediated equilibration (SME) during physical vapor deposition (PVD). Unlike intermolecular interactions, the role of intramolecular degrees of freedom in this process remains unexplored. Here, using experiments and coarse-grained molecular dynamics simulations, we demonstrate that varying dihedral rotation barriers of even a single bond, in otherwise isomeric molecules, can strongly influence the structure and stability of PVD glasses. These effects arise from variations in the degree of surface mobility, mobility gradients, and mobility anisotropy, at a given deposition temperature (Tdep). At high Tdep, flexible molecules have access to more configurations, which enhances the rate of SME, forming isotropic SGs. At low Tdep, stability is achieved by out of equilibrium aging of the surface layer. Here, the poor packing of rigid molecules enhances the rate of surface-mediated aging, producing stable glasses with layered structures in a broad range of Tdep. In contrast, the dynamics of flexible molecules couple more efficiently to the glass layers underneath, resulting in reduced mobility and weaker mobility gradients, producing unstable glasses. Independent of stability, the flattened shape of flexible molecules can also promote in-plane orientational order at low Tdep. These results indicate that small changes in intramolecular relaxation barriers can be used as an approach to independently tune the structure and mobility profiles of the surface layer and, thus, the stability and structure of PVD glasses.Funding Information
- National Science Foundation (DMREF-1628407, DMR-1720530, MRI-17-25969, CHE-1902509)
- Army Research Office (W911NF-17- 1-0282)
- XSEDE (TG-DMR150034)
This publication has 68 references indexed in Scilit:
- Measuring surface and bulk relaxation in glassy polymersThe European Physical Journal E, 2011
- Direct Measurement of Molecular Motion in Freestanding Polystyrene Thin FilmsJournal of the American Chemical Society, 2011
- Structural Variations of an Organic Glassformer Vapor-Deposited onto a Temperature Gradient StageThe Journal of Physical Chemistry Letters, 2011
- Molecular orientation in small-molecule organic light-emitting diodesJournal of Materials Chemistry, 2011
- Anisotropic Structure and Transformation Kinetics of Vapor-Deposited Indomethacin GlassesThe Journal of Physical Chemistry B, 2010
- Restricted Rotation in 9-Phenyl-anthracenes: A Prediction FulfilledOrganic Letters, 2010
- Orientation Control of Linear‐Shaped Molecules in Vacuum‐Deposited Organic Amorphous Films and Its Effect on Carrier MobilitiesAdvanced Functional Materials, 2010
- Hiking down the Energy Landscape: Progress Toward the Kauzmann Temperature via Vapor DepositionThe Journal of Physical Chemistry B, 2008
- Organic Glasses with Exceptional Thermodynamic and Kinetic StabilityScience, 2007
- Direct Imaging of Nanoparticle Embedding to Probe Viscoelasticity of Polymer SurfacesPhysical Review Letters, 2003