  Within a second virial theory, we study bulk phase diagrams as well as the
free planar isotropic-nematic interface of binary mixtures of nonadditive thin
and thick hard rods. For species of the same type the excluded volume is
determined only by the dimensions of the particles, whereas for dissimilar ones
it is taken to be larger or smaller than that, giving rise to a nonadditivity
that can be positive or negative. We argue that such a nonadditivity can result
from modelling of soft interactions as effective hard-core interactions. The
nonadditivity enhances or reduces the fractionation at isotropic-nematic ($IN$)
coexistence and may induce or suppress a demixing of the high-density nematic
phase into two nematic phases of different composition ($N_1$ and $N_2$),
depending on whether the nonadditivity is positive or negative. The interfacial
tension between co-existing isotropic and nematic phases show an increase with
increasing fractionation at the $IN$ interface, and complete wetting of the
$IN_2$ interface by the $N_1$ phase upon approach of the triple point
coexistence. In all explored cases bulk and interfacial properties of the
nonadditive mixtures exhibit a striking and quite unexpected similarity with
the properties of additive mixtures of different diameter ratio.
