(499i) Oscillatory Responses of Mechanically-Excited Sessile Drops and Polymer Balloons

Sessile drops and rubber balloons possess contrasting mechanical responses. Whereas the former exhibits the one-fold static behavior predicted by Young-Laplace equation, up to two folds exist on the same characteristic curve of the latter. With the coverage of soft polymer film on its free surface, a drop changes its static behavior and stability as a result of the re-enforced surface tension. The oscillatory modal responses vary accordingly, as the fluid inertia force and solid elasticity compete. Similar behaviors between resonating drops and balloons, such as their modal wave patterns and the corresponding harmonic and sub-harmonic responses, have been repeatedly observed in various experiments in spite of the apparent difference between the two media: a liquid versus a liquid-solid composite continuum. Such similarity in their dynamic responses essentially qualifies balloons as drops with a much higher effective surface tension. On the theoretical side we study mechanisms of symmetry-breaking and change of stability. On the application side, we manipulate geometric arrangements and topological configurations of rubber balloons for implementing active surfaces with adjustable binary properties.