Easy axis memorization with active control of the azimuthal anchoring energy in nematic liquid crystals

I show how to measure with a rotating magnetic field the azimuthal anchoring energy in a nematic liquid crystal. This technique is used to study the dynamics of memorization of an easy axis when a sample treated for planar sliding anchoring with a liquid polymer is maintained during a long time in a fixed magnetic field parallel to the glass plates. A method to actively control the anchoring energy is proposed. The classical model of passivation of the surface by the polymer is discussed in view of my results