  We investigate the universal orientation-dependent interactions between
non-spherical colloidal particles immersed in a critical solvent by studying
the instructive paradigm of a needle embedded in bounded two-dimensional Ising
models at bulk criticality. For a needle in an Ising strip the interaction on
mesoscopic scales depends on the width of the strip and the length, position,
and orientation of the needle. By lattice Monte Carlo simulations we evaluate
the free energy difference between needle configurations being parallel and
perpendicular to the strip. We concentrate on small but nonetheless mesoscopic
needle lengths for which analytic predictions are available for comparison. All
combinations of boundary conditions for the needles and boundaries are
considered which belong to either the "normal" or the "ordinary" surface
universality class, i.e., which induce local order or disorder, respectively.
We also derive exact results for needles of arbitrary mesoscopic length, in
particular for needles embedded in a half plane and oriented perpendicular to
the corresponding boundary as well as for needles embedded at the center line
of a symmetric strip with parallel orientation.
