How viscous bubbles collapse: topological and symmetry-breaking instabilities in geometrically-nonlinear Stokes flow in 2D*

Large floating viscous bubbles whose interior gas is rapidly depressurized exhibit a fascinating instability, whereby radial wrinkles permeate the liquid film in the course of its flattening (Debregeas et al, Science 1998; DaSilviera et al., Science 2000, Oratis et al., Science 2020). We address this instability by studying how Stokes flow in a curve film of a non-inertial incompressible liquid with free surfaces is generated by temporal variation of the curvature. We reveal the experimental observations of Oratis et al. as a universal, curvature-driven surface dynamics, imparted by viscous resistance to temporal variations of the surface's Gaussian curvature, whereby the depressurized bubble flattens by forming a radially moving front that separates a flat core and a spherically-shaped periphery, and becomes wrinkled due to a hoop-compressive stress at the wake of the propagating front. This novel surface dynamics has close ties to ``Jelium physics" in continuum media, where topological defects, akin to charges in electrostatic media, spontaneously emerge to screen elastic stresses.