Two Relaxation Mechanisms for Rejuvenation of Stable Polystyrene Glass

Area of Science:

• Materials Science
• Polymer Physics
• Physical Chemistry

Background:

• Glassy polymers like polystyrene (PS) exist in stable states.
• Thin films can be prepared via vapor deposition or physical aging.
• Rejuvenation is a process of heating these stable glassy states.

Purpose of the Study:

• To investigate the rejuvenation behavior of polystyrene thin films.
• To compare experimental results with simulation predictions.
• To identify potential new relaxation mechanisms in glassy PS.

Main Methods:

• Heating stable glassy films of polystyrene (PS) with varying thicknesses.
• Utilizing computer simulations with pre-obtained parameters.
• Analyzing deviations from model predictions for intermediate film thicknesses.

Main Results:

• Rejuvenation of PS films (h ≳ 200 nm and h ≲ 50 nm) is accurately predicted by simulations without free parameters.
• Films with intermediate thickness (h ∼ 140 nm) show complex behavior and deviate from predictions.
• Intermediate films, after rejuvenation and aging, are described by a single free parameter.

Conclusions:

• A new mechanism for PS glass rejuvenation is suggested.
• Two distinct relaxation processes are proposed to be involved.
• These processes appear to couple with the material density.