Local dynamic mechanical properties in model free-standing polymer thin films

Area of Science:

• Polymer Physics
• Materials Science
• Nanotechnology

Background:

• Dynamic mechanical properties (DMPs) of polymer thin films are crucial for their applications.
• Understanding surface effects on mechanical behavior is essential for film design.

Purpose of the Study:

• To investigate the local DMPs of free-standing polymer thin films.
• To analyze the influence of free surfaces on mechanical properties as a function of temperature and film thickness.

Main Methods:

• Utilized high-frequency sinusoidal oscillations on a coarse-grained polymer model.
• Calculated storage modulus (G') and loss modulus (G") across the film thickness.
• Examined DMPs in relation to position normal to the free surfaces.

Main Results:

• Identified mechanically soft layers near the free surfaces of glassy thin films.
• Observed that the thickness of these soft layers increases with temperature approaching the glass transition temperature (T(g)).
• Found that thin films exhibit a heterogeneous distribution of DMPs, with distinct melt-like and glass-like regions at T(g).

Conclusions:

• The presence of soft surface layers reduces the overall stiffness of glassy polymer thin films.
• The heterogeneous DMPs in thin films correlate with experimental observations.
• Findings provide insights into the mechanical behavior of thin polymer films, particularly near their glass transition.