The Marangoni effect causes liquid flow in response to surface energy gradients. In this study using a photosensitizer doped into poly(isobutyl methacrylate) (PiBMA) thin films, we direct this process by generating prescribed surface energy spatial patterns. At room temperature in the PiBMA glassy state, the photosensitizer is activated in light exposed regions. Upon heating, the photosensitizer can undergo grafting reactions and covalently bond to the PiBMA chain as the polymer liquefies. The grafting reactions change the surface energy of the film locally and, as a result, the polymer ?ows from low surface energy regions (unexposed to light) to high surface energy regions (exposed to light) according to the Marangoni effect. This ?ow creates smooth, three dimensional topography reflective of the light exposure pattern. 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. Such a photosensitizer polymer system was successfully demonstrated by activating the sensitizer with the visible (and small UV portion) light output of sunlight. The associated graphic shows optical microscopy images of the patterned samples using sunlight through various photomasks. Scale bars indicate 100 microns. We believe this methodology will be potentially useful as a facile and ubiquitous patterning technique for many polymers.

Patterning thin polymer films by photodirecting the Marangoni effect using photosensitizers

247th National Meeting (2014)

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