Vertically suspended smectic films with in-plane temperature gradients

We present a study of vertically suspended smectic films under the influenc e of temperature gradients in the film plane. It is shown that such gradien ts lead to the transport of smectic material, even against the action of th e gravitation forces, from the hot to the cold film edge, In addition, we o bserve thermally driven convection in these films, and it is demonstrated t hat the surrounding air plays an essential role for this instability. We co mpare this result with convective patterns in soap films reported by Martin and Wu in Phys. Rev. Lett, 80 1892 (98) and give some evidence that their interpretation has to be modified, the contact with surrounding air has to be taken into account.