Phase Behaviour of Dumbbell and Barbell Shaped Particles

Abstract

We investigate the phase behaviour of colloidal hard dumbbell and barbell shaped particles. We model dumbbell shaped particles as hard spherocylinders with a length-diameter ratio of L/D which carry spheres of diameter σ at both ends. For the barbell shaped particles, we modify these dumbbells by replacing the spheres with spherocylinders of length Le and diameter σ. Using Monte Carlo simulations, we map out the phase diagram of these particles for varying aspect ratios of length to diameter (L/D), sphere diameter to rod diameter (σ/D) and barbell end spherocylinders length to rod diameter (Le/D). As part of our study we investigate the stability of a possible cholesteric phase. Colloids and other achiral particles rarely exhibit a cholesteric phase, thus we take particular interest in investigating the existence of the cholesteric phase in this system. Our results show the destabilisation of the nematic phase, with respect to the isotropic phase, with increases of σ/D. In contrast increases in L/D stabilise the nematic phase. Additionally the spheres and spherocylinders destabilise the smectic phase and crystal phase but allow the formation of a columnar phase. The stability of the smectic phase decreases with Le/D.