Temporal evolution of relaxation in rubbed polystyrene thin films

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Understanding polymer dynamics is crucial for material properties.
• Rubbed polymer films exhibit unique relaxation behaviors.
• Polystyrene (PS) is a widely studied amorphous polymer.

Purpose of the Study:

• To investigate the temporal relaxation mechanisms in rubbed polystyrene (PS) thin films.
• To characterize the kinetics and activation energies of these relaxation processes.
• To determine the influence of molecular weight on relaxation dynamics.

Main Methods:

• Studied 50 nm thick rubbed polystyrene thin films.
• Probed relaxation by measuring the decay of optical anisotropy.
• Analyzed relaxation using single-exponential decay models and temperature dependence.

Main Results:

• Identified two single-exponential decay processes and a temperature-dependent constant.
• These relaxations are significantly faster than the alpha relaxation, with low activation energies (3.0 and 5.1 kcal/mol).
• Relaxation time constants were independent of molecular weight (13.7 K to 550 K Daltons) at the studied temperatures.

Conclusions:

• The observed fast relaxations are local in nature, distinct from the slower main chain (alpha) relaxation.
• These findings provide insight into the complex dynamics of thin polymer films.
• The molecular weight independence suggests these modes are not related to chain reptation.