In this paper we report a new method for determining the critical threshold of the Freedericksz transition driven by an electric field. It is based on the measurement of the amplitude of the molecule fluctuations as a function of the voltage differen
ce applied to a planar nematic cell. The precise measurement of the director fluctuations of the liquid crystal is made possible by the use of a very precise and sensitive polarization interferometer. The great advantage of the method is that it does not depend on complex fits as it is usually done in literature.
We report experimental and numerical evidences that the dynamics of the director of a liquid crystal driven by an electric field close to the critical point of the Freedericksz Transition(FT) is not described by a Landau-Ginzburg (LG) equation as it
is usually done in literature. The reasons are related to the very crude approximations done to obtain this equation, to the finite value of the anchoring energy and to small asymmetries on boundary conditions. We also discuss the difference between the use of LG equation for the statics and the dynamics. These results are useful in all cases where FT is used as an example for other orientational transitions.
