  Using Monte Carlo simulation, we analyse the behaviour of two-dimensional
hard rods in four different types of geometric confinement: (i) a slit pore
where the particles are confined between two parallel walls with homeotropic
anchoring; (ii) a hybrid slit pore formed by a planar and a homeotropic wall;
square cavities that frustrate the orientational order by imposing either (iii)
homeotropic or (iv) planar wall anchoring. We present results for the state
diagram as a function of the packing fraction and the degree of confinement.
Under extreme confinement, unexpected states appear with lower symmetries than
those of the corresponding stable states in bulk, such as the formation of
states that break the anchoring constraints or the symmetry imposed by the
surfaces. In both types of square cavities the particles form disclinations at
intermediate densities. At high densities, however, the elastic stress is
relaxed via the formation of domain walls where the director rotates abruptly
by ninety degrees.
