  A Landau theory is presented for the structural transition of electrically
stabilized colloidal crystals under shear. The model suggests that a structural
transition from an ordered layered colloidal crystal into a disordered
structure occurs at a critical shear stress. The shear induced structural
transition is related to a change of the rheological properties caused by the
variation of the microstructure which can be verified by scattering
experiments. The theory is used to establish the shape of the flow curves. A
good qualitative agreement with experimental results can be achieved, while a
scaling relation similar to the elastic scaling is established.
