Colloidal Aggregation in a Nematic Liquid Crystal: Topological Arrest of Particles by a Single-Stroke Disclination Line

We numerically study many-body interactions among colloidal particles suspended in a nematic liquid crystal, using a fluid particle dynamics method, which properly incorporates dynamical coupling among particles, nematic orientation, and flow field. Based on simulation results, we propose a new type of interparticle interaction in addition to well-known quadrupolar interaction for particles accompanying Saturn-ring defects. This interaction is mediated by the defect of the nematic phase: upon nematic ordering, a closed disclination loop binds more than two particles to form a sheetlike dynamically arrested structure. The interaction depends upon the topology of a disclination loop binding particles, which is determined by aggregation history.

Figure 1

Two types of defect formation processes around a pair of particles. A transient defect structure formed in the early stage ($\tilde{t}=30$) becomes unstable and transforms into either (a) the lowest energy structure stabilized by the quadrupolar interaction or (b) a new type of (quasi-)stable configuration, in which a single disclination loop is shared by two neighboring particles.

Figure 2

The aggregation process of particles immersed in a liquid crystal. A simulated box (${64}^3$) includes 50 particles of $\tilde{a}=3.5$ ($\Phi =3.43\%$). Particles bound by disclination lines are drawn as red ones.

Figure 3

Time development of $g(r)$. The inset shows a sheetlike planar aggregated structure composed of seven particles bound by a single-stroke defect loop.