Surface Adhesion of Back-Illuminated Ultrafast Laser-Treated Polymers

TL;DR

This study investigates how back-illumination ultrafast laser treatment alters the surface properties of polymers, leading to increased hydrophobicity primarily through morphological changes without chemical modifications.

Contribution

It demonstrates that back-illumination laser treatment causes surface blistering and increased hydrophobicity by confining chemical changes beneath the surface, unlike front-illumination methods.

Findings

Surface becomes more hydrophobic after back-illumination treatment.

Laser creates voids at the polymer-quartz interface without chemical surface changes.

Morphological changes, not chemical, drive increased hydrophobicity.

Abstract

We report a decreased surface wettability when polymer films on a glass substrate are treated by ultra-fast laser pulses in a back-illumination geometry. We propose that back-illumination through the substrate confines chemical changes beneath the surface of polymer films, leaving the surface blistered but chemically intact. To confirm this hypothesis, we measure the phase contrast of the polymer when observed with a focused ion beam. We observe a void at the polymer-quartz interface that results from the expansion of an ultrafast laser-induced plasma. A modified polymer layer surrounds the void, but otherwise the film seems unmodified. We also use X-ray photoelectron spectroscopy to confirm that there is no chemical change to the surface. When patterned with partially overlapping blisters, our polymer surface shows increased hydrophobicity. The increased hydrophobicity of back-illuminated surfaces can only result from the morphological change. This contrasts with the combined chemical and morphological changes of the polymer surface caused by a front-illumination geometry.