Segmental relaxations have macroscopic consequences in glassy polymer films

Area of Science:

• Polymer Physics
• Materials Science
• Surface Science

Background:

• Thin glassy polymer films exhibit physical aging, a process affecting their properties over time.
• Dewetting is a critical phenomenon in thin film stability and morphology evolution.
• Residual stresses in polymer films can significantly influence their behavior.

Purpose of the Study:

• To investigate the impact of physical aging on the dewetting behavior of thin spin-coated polystyrene films.
• To quantify the relationship between aging time and dewetting parameters like velocity, width, and height.
• To elucidate the underlying mechanisms responsible for stress relaxation during aging.

Main Methods:

• Detailed dewetting studies were performed on aged, thin spin-coated polystyrene films.
• Measurements of dewetting velocity, rim width, and rim height were correlated with aging time.
• Temperature dependence of relaxation times was analyzed using Arrhenius behavior to determine activation energy.

Main Results:

• A simultaneous and rapid exponential decay in dewetting velocity, width, and height was observed with increasing aging time.
• The decay kinetics were found to be temperature-dependent, following Arrhenius behavior.
• An activation energy of 70±6 kJ/mol was determined, comparable to polystyrene's β-relaxation.

Conclusions:

• Physical aging in polystyrene films leads to a reduction in residual stresses.
• Chain segment rearrangements are sufficient to relax frozen-in conformations and residual stresses.
• These molecular rearrangements may also drive macroscopic relaxations observed at polymer surfaces.