  The dilute lamellar phase of the nonionic surfactant C$_{12}$EO$_5$ was doped
with goethite (iron oxide) nanorods up to a fraction of 5 vol. %. The
interaction between the inclusions and the host phase was studied by polarized
optical microscopy (with or without an applied magnetic field) and by
small-angle X-ray scattering. We find that, when the orientation of the
nanorods is modified using the magnetic field, the texture of the lamellar
phase changes accordingly; one can thus induce a homeotropic-planar
reorientation transition. On the other hand, the lamellar phase induces an
attractive interaction between the nanorods. In more concentrated lamellar
phases (under stronger confinement) the particles form aggregates. This
behavior is not encountered for a similar system doped with spherical
particles, emphasizing the role of particle shape in the interaction between
doping particles and the host phase.
