Azimuthal anchoring of nematic on undulated substrate: Elasticity versus memory

We measure the azimuthal anchoring energy of the nematic 5CB on sinusoidal holographic unidimensional and bidimensional gratings. We find that the anc horing strength is almost the same for all of the gratings and up to one or der of magnitude stronger than expected by the topographic mechanism propos ed by Berreman. We observe strong memory effects which dominate both the el astic anchoring and the easy axis gliding. We show that these memory effect s limit from below the anchoring energy and are the main obstacle in the re alization of substrates with weak anchoring conditions.