Glassy boundary layers vs enhanced mobility in capped polymer films.

Area of Science:

• Polymer Physics
• Materials Science
• Computational Chemistry

Background:

• Confined polymer dynamics are crucial for material properties.
• Understanding substrate-polymer interactions is key to controlling polymer behavior.
• Heterogeneity in segmental dynamics affects macroscopic properties.

Purpose of the Study:

• Investigate the influence of substrate interactions and confinement on AB-copolymer dynamics.
• Elucidate the mechanisms behind non-monotonic segmental mobility.
• Analyze the role of finite-size effects and boundary layers.

Main Methods:

• Coarse-grained molecular-dynamics simulations.
• Systematic variation of substrate-polymer interaction strength.
• Systematic variation of film thickness (substrate distance).

Main Results:

• Observed non-monotonic dependence of film-averaged segmental mobility on substrate attraction strength.
• Identified highly heterogeneous segmental dynamics: slowed near substrates, enhanced in film center.
• Demonstrated strong dependence on film thickness due to finite-size effects and glassy boundary layers.

Conclusions:

• Film-averaged mobility is insufficient to understand confined polymer dynamics.
• Local mobility variations are critical for interpreting simulation and experimental results.
• Finite-size effects and glassy boundary layers significantly impact confined polymer dynamics.