Viscoelastic leveling of annealed thin polystyrene films

Area of Science:

• Materials Science
• Polymer Physics
• Nanotechnology

Background:

• Understanding nanoscale viscoelastic flow is critical for advanced material processing.
• Polystyrene melts exhibit complex flow behavior above their glass transition temperature (T(g)).
• Topographical evolution during film reflow dictates surface properties and device performance.

Purpose of the Study:

• To investigate the viscoelastic flow behavior of patterned polystyrene films at the nanoscale.
• To characterize the topographical consequences of reflow rather than the temporal dynamics.
• To determine the relationship between surface topography, material properties, and annealing conditions.

Main Methods:

• Theoretical modeling using capillary wave theory and reptation theory.
• Experimental characterization of submicrometer polystyrene films using atomic force microscopy.
• Thermal nanoimprint technology for sample preparation and annealing at controlled temperatures (T(g) + 10 °C to T(g) + 50 °C).

Main Results:

• Short spatial wavelengths of topography exhibit elastic behavior, while long wavelengths show viscous decay.
• A threshold wavelength separates elastic and viscous regimes, dependent on surface tension and elastic plateau modulus.
• This threshold is a nanoscale parameter for polystyrene, weakly influenced by annealing temperature.

Conclusions:

• Nanoscale viscoelasticity governs the reflow of patterned polystyrene films.
• Capillary wave theory effectively describes the dual elastic-viscous nature of surface topography evolution.
• The findings provide insights into controlling surface morphology in thin polymer films for nanotechnology applications.