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Surface wrinkling of freely-floating smectic bubbles

Bubbles made of smectic liquid crystals (LC) can display buckling and wrinkling. These deformations are induced in the course of the relaxation of an elongated bubble towards a sphere. The bubbles are created through the collapse of a catenoid LC film. Two mechanisms leading to wrinkles are reported: (a) Compression of the smectic film by outer forces, and (b) Invagination of the bubble shortly after formation. The flow on the bubble surface is analyzed, providing insight into how the outer forces act on the bubble and induce local surface deformation. It is found that the orientation of the wrinkles depends on the direction of the acting force. The wavelength of the wrinkles is analyzed over time. Additionally, the formation of small protrusions outside the film area (i.e., tubuli) is described.