Freely suspended smectic films with in-plane temperature gradients

Freely suspended smectic films with in-plane temperature inhomogeneities can exhibit remarkable thermocapillary (Marangoni) effects. The temperature dependence of the surface tension sigma (T) promotes flow in the film plane, convection roll patterns, and climbing of smectic layers against gravitational forces. We discuss several experimental geometries where macroscopic material transport is driven by temperature gradients, including experiments under normal gravity and observations in microgravitation during suborbital rocket flights and on the International Space Station. In all these experiments, the temperature dependence of the surface tension drives unidirectional material flow. The divergence of this flow near the hot and cold film edges, and at the boundaries of film islands in the film, is associated with the creation, motion and removal of dislocations. These dissipative processes limit the flow velocity.