Corona-treated polyethylene films are macroscopic charge bilayers

Area of Science:

• Materials Science
• Surface Science
• Polymer Science

Background:

• Corona discharge is a common surface treatment for polymers like polyethylene (PE).
• Previous studies indicated surface oxidation and changes in wetting properties after corona treatment.
• Unexpected findings suggested a more complex electrical phenomenon at play.

Purpose of the Study:

• To investigate the electrical, chemical, and morphological changes on both surfaces of PE films after corona discharge.
• To understand the mechanism behind the formation of an electric bilayer.
• To explore the implications for surface engineering and material properties.

Main Methods:

• Exposure of polyethylene films to corona discharge.
• Analysis of surface electrostatic potentials.
• Characterization of surface wetting behavior.
• Assessment of chemical composition using spectroscopy.
• Microscopic examination of surface morphology.

Main Results:

• Corona-treated PE films exhibit large and opposite electrostatic potentials on top and bottom surfaces, forming an electric bilayer.
• The top surface becomes hydrophilic, rougher, and oxidized due to phase separation and dewetting.
• The bottom surface, while charged, remains chemically unaltered, morphologically unchanged, and non-wettable.
• Extraction of oxidized material from the top surface by common liquids explains adhesive joint failures in corona-treated thermoplastics.
• Poling of one surface induces a distinct charge build-up on the opposite surface with preserved properties.

Conclusions:

• Corona discharge induces a dual surface modification in PE films, creating an electric bilayer with distinct properties.
• The unoxidized, charged bottom surface offers novel opportunities for surface engineering without altering intrinsic material characteristics.
• Understanding these surface phenomena is crucial for optimizing the performance and durability of corona-treated polymer applications.