Interplay between dynamic heterogeneity and interfacial gradients in a model polymer film

Area of Science:

• Materials Science
• Physical Chemistry
• Soft Matter Physics

Background:

• Glass-forming liquids show dynamic heterogeneity, with regions relaxing at different rates.
• Interfaces introduce gradients in glass transition temperature (Tg) and relaxation time (τ).
• The interplay between bulk and interfacial heterogeneity is poorly understood.

Purpose of the Study:

• Investigate how bulk dynamic heterogeneity influences and is influenced by interfacial gradients in polymer thin films.
• Clarify the relationship between dynamic heterogeneity and interfacial effects in glass-forming liquids.

Main Methods:

• Utilized molecular dynamics simulations.
• Employed the isoconfigurational ensemble.
• Studied polymer thin films to analyze dynamics at the nanoscale.

Main Results:

• Surface relaxation time (τ) spectrum is broader but shifted to shorter times compared to the bulk.
• Surface dynamics exhibit less spatial correlation than bulk dynamics.
• Slow dynamics extend further into the film than fast dynamics at the interface.

Conclusions:

• Surface gradients in dynamics are distinct from bulk heterogeneity and do not simply reflect a higher