Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films

Stephen Mirigian, Kenneth S Schweizer

Research output: Contribution to journalArticle

Abstract

We have constructed a quantitative, force level, statistical mechanical theory for how confinement in free standing thin films introduces a spatial mobility gradient of the alpha relaxation time as a function of temperature, film thickness, and location in the film. The crucial idea is that relaxation speeds up due to the reduction of both near-surface barriers associated with the loss of neighbors in the local cage and the spatial cutoff and dynamical softening near the vapor interface of the spatially longer range collective elasticity cost for large amplitude hopping. These two effects are fundamentally coupled. Quantitative predictions are made for how an apparent glass temperature depends on the film thickness and experimental probe technique, the emergence of a two-step decay and mobile layers in time domain measurements, signatures of confinement in frequency-domain dielectric loss experiments, the dependence of film-averaged relaxation times and dynamic fragility on temperature and film thickness, surface diffusion, and the relationship between kinetic experiments and pseudo-thermodynamic measurements such as ellipsometry.

Original languageEnglish (US)
Article number24470
JournalJournal of Chemical Physics
Volume143
Issue number24
DOIs
StatePublished - Dec 28 2015

Fingerprint

vitrification
Vitrification
Surface diffusion
surface diffusion
Film thickness
film thickness
Thin films
Relaxation time
gradients
thin films
relaxation time
Ellipsometry
Dielectric losses
dielectric loss
softening
Temperature
ellipsometry
temperature
Elasticity
cut-off

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Theory of activated glassy relaxation, mobility gradients, surface diffusion, and vitrification in free standing thin films. / Mirigian, Stephen; Schweizer, Kenneth S.

In: Journal of Chemical Physics, Vol. 143, No. 24, 24470, 28.12.2015.

Research output: Contribution to journalArticle

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