Spin Dewetting of Ultrathin Polymer Films

Area of Science:

• Materials Science
• Surface Science
• Fluid Dynamics

Background:

• Spin coating is a standard method for creating ultrathin films.
• Continuous film formation fails with very dilute polymer solutions on defect-free substrates.
• This failure is often misattributed to surface defects.

Purpose of the Study:

• Investigate the formation of droplet arrays from dilute polymer solutions during spin coating.
• Identify the underlying mechanism driving this phenomenon.
• Explore parametric effects on droplet formation and its potential for patterning.

Main Methods:

• Spin coating of extremely dilute polymer solutions on flat substrates.
• Observation and analysis of droplet formation and arrangement.
• Systematic variation of solution concentration and other parameters.

Main Results:

• Reproducible formation of isotropic polymer droplet arrays, independent of substrate defects.
• Identification of spin dewetting, driven by Marangoni effect, as the cause.
• Droplet size and periodicity decrease with increasing polymer concentration.
• Evaporation-mediated Marangoni stress is the primary driver, contrasting with disjoining pressure.

Conclusions:

• Spin dewetting is a novel phenomenon occurring during spin coating of dilute polymer solutions.
• The process is governed by Marangoni stresses, not surface defects.
• Spin dewetting offers a rapid, reproducible, and ultrafast meso-patterning technique.