Recently, amorphous films of small molecules formed via physical vapor deposition (PVD) have been shown to exhibit remarkable thermodynamic and kinetic properties, equivalent to those that have been aged for time scales on the order of hundreds of years. Previous experiments and simulations suggest that the stability differences observed in these PVD glass films are the result of enhanced mobility near the free surface, such that molecules are allowed to sample a greater number of configurations before becoming trapped by subsequent deposited layers. However, much remains to be learned about the effects of properties like molecular shape and rotational freedom on the stability and morphology of these PVD amorphous packings. By using molecular dynamics simulations to mimic the PVD process of coarse-grained small molecules, we can make fine-tuned changes to these properties and then closely observe changes in films, both during and after the deposition process. Notably, we can then potentially make a connection between changes in internal degrees of freedom and the corresponding molecular entropy and changes in PVD film properties. Thus far, we suggest that molecules which exhibit greater entropy in their supercooled liquid state, at a common temperature relative to the glass transition, create more stable PVD glass films.

Effects of internal degrees of freedom on simulated vapor deposited glass films

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.