Nature of anisotropic fluctuation modes in ordered systems

The nature of anisotropic fluctuation modes in an ordered system is analyse d using general symmetry arguments. It is shown that the anisotropic fluctu ation modes in a periodic phase can be classified using a wave vector withi n the irreducible Brillouin zone and a band index. The spatial pn,files of the fluctuation modes are described by Bloch functions. These general featu res enable a study of the stability and kinetic pathway of complex ordered polymeric structures to be carried out. The utility of the theory is illust rated using the Landau-Brazovskii theory of weak crystallization.