Classes of radial wrinkle patterns in capillary wrinkling

We investigated capillary force induced wrinkling of polymer (PS, PMMA, and Cytop™ (poly(perfluoro(1-butenyl vinyl ether)) films, floating on an air-water interface. As previously studied, this wrinkle pattern is generated by the capillary force exerted by a water droplet placed at the center of the floating film. When a large range of film thickness is used (10 nm to 1 μm) we observe a qualitative change in the wrinkle pattern in three different thickness regimes: In the thickest films (600 nm ~ 1 μm) a single wave number is seen throughout the bulk of the pattern. In intermediate thickness films (50 nm ~ 600 nm), the bulk wave mode cascades into higher wavenumber close to the contact line. In the thinnest films (10 nm ~ 50 nm) the high wavenumber mode is decorated with a lower frequency component. We will discuss possible mechanistic causes for these distinct patterns.