Cover Image, Volume 51, Issue 7


original image

The image shows an optical micrograph of a topographic feature formed in a thin polystyrene film by the Marangoni effect, as presented on page 535 by Christopher J. Ellison and colleagues. A photochemically patterned surface energy gradient is first programmed in the solid state. Two successive exposure steps are performed, each employing a mask with a regular array of lines and spaces, but different line periodicity and alignment direction. The thickness variations, represented by the brilliant interference colors in the optical micrograph, develop after heating the film above the glass transition temperature where the polymer flows from unexposed, lower surface energy regions to exposed, higher surface energy regions.