Numerical study of the phase behavior of rod-like colloidal particles with attractive tips

Suspensions of anisometric particles are known to self-assemble into various liquid crystal (LC) phases, namely, the nematic, smectic (A or B or both), and in some cases, columnar phases, due to the effects of excluded volume. For some applications, LC phases with higher degrees of order are desired, but due to the fact that these phases generally exist at larger volume fractions, they can be difficult to handle experimentally. Here, we explore the effect of a weak attractive interaction localized at the tips of rod-like particles on the phase behavior of these suspensions. We perform large-scale molecular dynamics simulations of rigid rod-like particles with both monodispersed and polydispersed lengths and a variety of aspect ratios. The rods are composed of rigidly connected beads, and the inter-rod bead interactions are modeled with a combination of Weeks–Chandler–Anderson and Lennard-Jones potentials. By increasing rod-tip attraction, we observe a favoring of the higher order smectic phase over the lower order nematic phase at lower volume fractions. With sufficiently strong rod-tip attraction, the nematic phase is removed from the phase diagram. Furthermore, we show how polydispersity influences this competition between LC phases.