Columnar versus smectic order in binary mixtures of hard parallel spherocylinders

Abstract

We present Monte Carlo simultions of binary mixtures of hard parallel spherocylinders with length-to-width ratios ${\mathit{L}}_1$/D=1.0 and ${\mathit{L}}_2$/D ranging from 1.3 to 2.1. The composition is such that the partial volume fractions are equal. For ${\mathit{L}}_2$/D>1.6, we observe a thermodynamically stable columnar phase which is not formed by the monodisperse components separately. The nematic-smectic transition, which is postponed by increasing the ${\mathit{L}}_2$/D ratio, is eventually preempted by a nematic-columnar transition for ${\mathit{L}}_2$/D>1.9, showing that in these mixtures bidispersity favors columnar order over smectic order.