  We study both theoretically and experimentally anchoring properties of
photoaligning azo-dye films in contact with a nematic liquid crystal depending
on photoinduced ordering of azo-dye molecules. In the mean field approximation,
we found that the bare surface anchoring energy linearly depends on the azo-dye
order parameter and the azimuthal anchoring strength decays to zero in the
limit of vanishing photoinduced ordering. From the absorption dichroism spectra
measured in the azo-dye films that are prepared from the azo-dye derivative
with polymerizable terminal groups (SDA-2) we obtain dependence of the dichroic
ratio on the irradiation dose. We also measure the polar and azimuthal
anchoring strengths in nematic liquid crystal (NLC) cells aligned by the
azo-dye films and derive the anchoring strengths as functions of the dichroic
ratio. Though linear fitting of the experimental data for both anchoring
strengths gives reasonably well results, it, in contradiction with the theory,
predicts vanishing of the azimuthal anchoring strength at certain nonzero value
of the azo-dye order parameter. By using a simple phenomenological model we
show that this discrepancy can be attributed to the difference between the
surface and bulk order parameters in the films.
