Nematic liquid-crystal alignment on stripe-patterned substrates

Here, we use molecular simulation to consider the behavior of a thin nematic film confined between two identical nanopatterned substrates. Using patterns involving alternating stripes of homeotropic-favoring and homogeneous-favoring substrates, we investigate the influence of the relative stripe width and the film thickness. From this, we show that the polar anchoring angle can be varied continuously from planar to homeotropic by appropriate tuning of these parameters. For very thin films with equal stripe widths, we observe orientational bridging, the surface patterning being written in domains which traverse the nematic film. This dual-bridging-domain arrangement breaks down with increase in film thickness, however, being replaced by a single tilted monodomain. Strong azimuthal anchoring in the plane of the stripe boundaries is observed for all systems.

Figure 1

(Color online) Schematic representation of the geometry used for the HNW particle-substrate interaction [16].

Figure 2

(Color online) Schematic representation of stripe-patterned systems with alternating homeotropic-inducing (red or dark) and planar-inducing (green or light) substrate regions.

Figure 3

(Color online) Snapshots of the 50:50 stripe-patterned system at a series of reduced densities. Color coding is used to indicate particle orientation.

Figure 4

(Color online) Density profiles for the 50:50 stripe-patterned system at different average densities ${\rho }^{\ast }$.

Figure 5

(Color online) Time series showing the director components for 500 configurations in the ${\rho }^{\ast }=0.4$ production run.

Figure 6

(Color online) Density-dependent profiles of the diagonal components of the order tensor, homeotropic-confined region.

Figure 7

(Color online) Density-dependent profiles of the diagonal components of the order tensor, planar-confined region.

Figure 8

(Color online) Density-dependent profiles of the off-diagonal component $Q_{yz}\left(z\right)$ of the order tensor for (a) homeotropic-confined region and (b) planar-confined region.

Figure 9

(Color online) Histogram representing the particle azimuthal angle distribution in the planar surface region for the stripe-patterned system with 50% H and 50% P coverage on the surfaces, ${\rho }^{\ast }=0.39$.

Figure 10

(Color online) Snapshots of the stripe-patterned system for different coverages of the homeotropic-confining and planar-confining substrate conditions, ${\rho }^{\ast }=0.4$.

Figure 11

(Color online) Comparison of ${\theta }_y$ and ${\theta }_z$ values in the two regions.

Figure 12

(Color online) Snapshots of striped systems with different $L_z$ values at ${\rho }^{\ast }=0.4$.

Figure 13

(Color online) $L_z=6\kappa {\sigma }_0$: profiles corresponding to the two surface regions.

Figure 14

(Color online) $L_z=8\kappa {\sigma }_0$: profiles corresponding to the two differently confined subsystems.

Figure 15

(Color online) Variation of ${\theta }_y$ and ${\theta }_z$ in the homeotropic-confined (H) and planar-confined (P) regions for different film thicknesses $L_z$.