Partial dewetting of polyethylene thin films on rough silicon dioxide surfaces

Area of Science:

• Materials Science
• Surface Science
• Polymer Physics

Background:

• Dewetting of thin polymer films is crucial for applications.
• Surface roughness is a common feature of real-world substrates.
• Understanding dewetting on rough surfaces is essential for controlling film morphology.

Purpose of the Study:

• To investigate the effect of substrate roughness on the dewetting behavior of polyethylene (PE) thin films.
• To compare dewetting on smooth versus rough silicon dioxide (SiO2) surfaces.
• To elucidate the mechanism behind partial dewetting on rough surfaces.

Main Methods:

• Preparation of smooth (0.3 nm RMS roughness) and rough (3.2-3.9 nm RMS roughness) SiO2 substrates.
• Deposition of ~80 nm thick PE films using spin-coating.
• In-situ observation of dewetting and crystallization using hot-stage optical microscopy.
• Characterization of residual film thickness and distribution using ellipsometry and X-ray reflectometry.

Main Results:

• Polyethylene films completely dewet on smooth SiO2 substrates.
• Partial dewetting was observed on rough SiO2 substrates, with a residual film of a few nanometers.
• X-ray reflectometry revealed polymer impregnation within the cavities of the rough surface.
• The residual film formation is attributed to the polymer fluid filling the surface cavities.

Conclusions:

• Substrate roughness fundamentally alters polymer thin film dewetting behavior.
• Partial dewetting, driven by surface impregnation, is a novel phenomenon with practical implications.
• The findings are relevant for applications involving thin polymer films on naturally rough surfaces.