Surface adhesion of back-illuminated ultrafast laser-treated polymers

We report a decreased surface wettability when polymer films on a glass substrate are treated by ultrafast 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 imaged 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.

Automated summary

The study found that using ultrafast laser pulses in a back-illumination geometry could decrease the surface wettability of polymer films while keeping the surface chemistry intact. Various methods were used to confirm this hypothesis, resulting in the discovery that back-illuminated surfaces showed increased hydrophobicity, which was different from the combined chemical and morphological changes caused by a front-illumination geometry.