Orientation-dependent depletion interaction in rodlike colloid-polymer mixtures

Depletion interaction in a suspension of rodlike colloids with added non-ad sorbing polymer coils is theoretically studied. We calculate an overlap vol ume of depletion zone between two rodlike colloids, based on the second vir ial approximation. We examine nematic-isotropic phase transition (NIT) and two-phase coexistence between an isotropic and a nematic phase at low polym er concentrations. We find that the depletion interaction is dependent on t he orientational order parameter of rodlike colloids and leads to a decreas e in the NIT concentration oil the addition of polymer. The coexistence cur ves have a leaning-chimney shape and are shifted to lower rod concentration s on increasing the polymer concentration.