title: Phenomenological model for the optically induced easy direction.
abstract: We present a phenomenological model to interprete the optically induced easy direction in a nematic cell in the slab approximation. One of the surfaces of the sample is supposed to give strong anchoring, whereas the other, covered with photosensible material, very weak anchoring. We assume that a surface nematic molecule is submitted to a potential connected with its interaction with the surface easy direction, with the surface nematic field, and with the optical induced anisotropy. The case in which the coupling with the nematic order in the bulk is important is considered too. A differential equation for the time evolution of the surface director is proposed, in which the viscous torque is balanced by the torque related to the surface fields. We show that our theoretical predictions are in agreement with experimental data on the optical induced surface orientation. The dependence of the anchoring energy strength on the irradiation time for dye-doped liquid crystals is also investigated.
authors.affiliation: Departamentul de Fizica, Universitatea Politehnica din Bucuresti, Splaiul Independentei 313, Ro-060042 Bucharest, Romania.
authors.forename: A L
authors.initials: AL
authors.lastname: Alexe-Ionescu
authors.forename: C
authors.initials: C
authors.lastname: Uncheselu
authors.forename: L
authors.initials: L
authors.lastname: Lucchetti
authors.forename: G
authors.initials: G
authors.lastname: Barbero