Biphasic, Lyotropic, Active Nematics

We perform dynamical simulations of a two-dimensional active nematic fluid in coexistence with an isotropic fluid. Drops of active nematic become elongated, and an effective anchoring develops at the nematic-isotropic interface. The activity also causes an undulatory instability of the interface. This results in defects of positive topological charge being ejected into the nematic, leaving the interface with a diffuse negative charge. Quenching the active lyotropic fluid results in a steady state in which phase-separating domains are elongated and then torn apart by active stirring.

Figure 1

Evolution with time of an initially circular drop of extensile active fluid. The nematic phase is white, and the isotropic phase is blue. The black lines show the scaled director $S\mathbf{n}$.

Figure 2

(a) Schematic illustration showing the tangential force and resulting flow field for different director orientations (thick black lines) at the interface. (b) Schematic illustration of the forces acting at a curved interface.

Figure 3

Interface instability and defect formation in a stripe of extensile active nematic, with time running from (a) to (d). For panels (c) and (d), the right-hand side shows the charge density $q$, with dark (light) shades corresponding to positive (negative) charge. We omit charge density plots for (a) and (b) since there is little separation of charge at these stages.

Figure 4

A typical configuration of the concentration $\varphi$ and the director in the steady state of a system with 50% nematic and activity $\chi =0.005$. The right panel is an enlargement of the orange square.

Figure 5

Plots of the radial averages of the correlation functions $c_{\parallel }$ (red circles) and $c_{\perp }$ (blue squares) against radial distance $d$ for 50% nematic mixtures with (a) $\chi =0.005$ (extensile) at the steady state, (b) $\chi =0.0001$ at the steady state, and (c) $\chi =0$ (passive) at a point in time during the phase separation process.

Figure 6

Charge density $q$ shown for a $275\times 275$ area of the simulation box for (a) 100% nematic with $\chi =0.005$, (b) 50% nematic with $\chi =0.005$, and (c) 50% nematic with $\chi =0$.