  Recent experiments indicate that doping low concentrations of bent-core
molecules into calamitic smectic solvents can induce anticlinic and biaxial
smectic phases. We have carried out Monte Carlo (MC) simulations of mixtures of
rodlike molecules (hard spherocylinders with length/breadth ratio $L_{\rm
rod}/D = 5$) and bow- or banana-shaped molecules (hard spherocylinder dimers
with length/breadth ratio $L_{ban}/D = 5$ or 2.5 and opening angle $\psi$) to
probe the molecular-scale organization and phase behavior of rod/banana
mixtures. We find that a low concentration (3%) of $L_{ban}/D = 5$ dimers
induces anticlinic (SmC$_A$) ordering in an untilted smectic (SmA) phase for
$100^\circ \le \psi < 150^\circ$. For smaller $\psi$, half of each bow-shaped
molecule is nanophase segregated between smectic layers, and the smectic layers
are untilted. For $L_{ban}/D = 2.5$, no tilted phases are induced. However,
with decreasing $\psi$ we observe a sharp transition from {\sl intralamellar}
nanophase segregation (bow-shaped molecules segregated within smectic layers)
to {\sl interlamellar} nanophase segregation (bow-shaped molecules concentrated
between smectic layers) near $\psi = 130^\circ$. These results demonstrate that
purely entropic effects can lead to surprisingly complex behavior in rod/banana
mixtures.
