(356h) Patterning Polystyrene Thin Films By Photodirecting Marangoni Convective Flow

The Marangoni effect causes liquids to flow in response to local surface energy gradients. We recently developed a method for photochemically directing this effect by generating prescribed surface energy spatial patterns in glassy polystyrene (PS) thin films. UV irradiation through a photo-mask selectively dehydrogenates the PS backbone locally, thus increasing surface energy in the UV exposed regions compared to the unexposed regions.  As a result, the polymer flows from low to high surface energy regions according to the Marangoni effect upon subsequent thermal annealing above the glass transition temperature. This flow creates smooth, three dimensional topography reflective of the original light exposure pattern. A theoretical framework that gives a more thorough understanding of the physics of this process, its limits and ways to apply it efficiently for various target metrics, such as the feature periodicity and feature height will also be presented along with comparisons between simulative predictions and experimental observations.

Finally, while PS dehydrogenation can be used to produce a variety of topographical patterns, incorporating the near UV and visible light photosensitizer 9,10-dibromo-anthracene (DBA) into PS films enables significant improvements in feature aspect ratio compared to the absence of such a sensitizer. This suggests a judicious selection of the photosensitizing compound in an otherwise transparent polymer expands the use of this method with more readily available and safer visible light sources.