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Updated: May 6, 2026
09:32
Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
Published on: January 26, 2016
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Crossover to surface flow in supercooled unentangled polymer films
Chi-Hang Lam1, Ophelia K C Tsui
1Department of Applied Physics, Hong Kong Polytechnic University, Hung Hom, Hong Kong, China.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|November 16, 2013
Summary
Glassy polymer flow differs above and below the glass transition temperature (Tg). Below Tg, a mobile surface layer drives transport independent of film thickness, matching experimental observations.
Area of Science:
- Polymer Physics
- Materials Science
- Soft Matter Physics
Background:
- Understanding the flow behavior of glassy polymers is crucial for material design.
- Previous studies suggested surface effects influence polymer film dynamics, but direct evidence was limited.
Purpose of the Study:
- To investigate the driven flow of unentangled glassy polymer films.
- To elucidate the role of film thickness and temperature on polymer flow dynamics.
- To identify the mechanism behind surface transport in glassy polymer films.
Main Methods:
- Nonequilibrium molecular dynamics simulations using a bead-spring model.
- Analysis of polymer film mobility as a function of film thickness and temperature.
- Comparison of simulation results with experimental data on capillary wave evolution.
Main Results:
- Above the glass transition temperature (Tg), polymer flow follows Poiseuille's law, with mobility scaling with film thickness (h^3).
- Below Tg, film mobility becomes independent of thickness, indicating dominant surface transport.
- A distinct mobile surface layer with an exponentially decaying velocity profile was identified.
Conclusions:
- A mobile surface layer is responsible for the thickness-independent transport below Tg.
- The simulation findings align with recent experimental observations of polystyrene films.
- This study provides a molecular-level understanding of surface-driven flow in glassy polymers.
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