The investigation of instabilities of complex fluids under external fields is motivated by several important aspects. First, detection of the onset allows very precise measurements of relevant material parameters, which very often cannot be measured directly. Second, depending on the nature of the complex fluid, a host of different external fields, like electric and magnetic fields, temperature and concentration gradients, flow and mechanical fields, can be used to drive the system out of equilibrium. Third, in complex fluids even first instabilities can show non-trivial features, thus allowing a rather detailed theoretical description of complicated instability types as well as a quantitative comparison with experiments.
Advanced topics are concerned with the spatial structures above onset, their defects and dynamics.
In particular, smectic films under external electric fields are considered. The advantage of using films lies in their superior visualization properties and in the possibility to explore new geometries in the experimental setup. At the moment we describe the onset of reorientation by a shear induced Helfrich-Hurault type instability using generalized hydrodynamic equations suitable for layered systems.