Shear instabilities of freely standing thermotropic smectic-A films

In this Letter we discuss theoretically the instabilities of thermotropic f reely standing smectic-A films under shear flow [3]. We show that, in Couet te geometry, the centrifugal force;pushes the liquid crystal toward the out er boundary and induces smectic layer dilation close to the outer boundary. Under strong shear, this effect induces a layer buckling instability. The critical shear rate is proportional to 1/root d, where d is the thickness o f the film.