  Within the Onsager theory we study free planar isotropic-nematic interfaces
in binary mixtures of hard rods. For sufficiently different particle shapes the
bulk phase diagrams of these mixtures exhibit a triple point, where an
isotropic (I) phase coexists with two nematic phases ($N_1$ and $N_2$) of
different composition. For all explored mixtures we find that upon approach of
the triple point the $IN_2$ interface shows complete wetting by an intervening
$N_1$ film. We compute the surface tensions of isotropic-nematic interfaces,
and find a remarkable increase with fractionation, similar to the effect in
polydisperse hard-rod fluids.
