How do crumples impact the stiffness of ultrathin polymer films?

Handling of polymer films becomes increasingly difficult as film thickness decreases. Liquid support layers are often used to ease the manipulation of these films. Here, we demonstrate that a hydrophilic polymer film, poly (methyl methacrylate), can be reversibly folded and unfolded from liquid surfaces resulting in crumples, creases, and folds forming in the film. We investigate the impact of film thicknesses and area on the resultant crumples and how crumples impact the mechanical properties. These results provide new fundamental insights into how polymer behavior is altered due to changes in the ultrathin film geometry upon crumpling the films.