  We demonstrate spontaneous wrinkling as a transient dynamical pattern in thin
freely floating smectic liquid-crystalline films. The peculiarity of such films
is that, while flowing liquid-like in the film plane, they cannot quickly
expand in the direction perpendicular to that plane. At short time scales they
therefore behave in two dimensions like quasi-incompressible membranes. Such
films can develop a transient undulation instability or form bulges in response
to lateral compression. Optical experiments with freely floating bubbles on
parabolic flights and in ground lab experiments are reported. The
characteristic wavelengths of the wrinkles are in the submillimeter range. We
demonstrate the dynamic nature of the pattern formation mechanism and develop a
basic model for the wavelength selection and wrinkle orientation.
