Fast-switching chiral nematic liquid-crystal mode with polymer-sustained twisted vertical alignment

We demonstrate a fast-switching liquid-crystal mode with polymer-sustained twisted vertical alignment. By optimizing the polymerization condition, a polymer microstructure with controlled orientation is produced. The polymer microstructure not only synergistically suppresses the optical bounce during field-induced homeotropic-twist transition but also shortens the response time significantly. Theoretical analyses validate that the ground state free energy density is modified by the aligning field of the polymer microstructure, which affects the driving voltage of the device. The outcomes of this paper will enable the development of fast-switching and achromatic electro-optical and photonic devices.

Figure 1

Operation schematic of PS-TVA mode. Yellow/light gray ellipse, LC; green/dark gray ellipse, polymers.

Figure 2

(a) Static voltage response of TVA and PS-TVA mode with different curing voltages. (b) Contrast ratio of PS-TVA with different curing voltages (red circles) and simulated director profile: pretilt angle (purple diamond) and total twist angle (green cross).

Figure 3

POM images of (a) TVA mode, 0 V; (b) TVA mode, 14.5 V; (c) PS-TVA mode ($V_{\mathrm{cur}}=3\mathrm{V}$), 0 V; (d) PS-TVA mode ($V_{\mathrm{cur}}=3\mathrm{V}$), 13.4 V; (e) PS-TVA mode ($V_{\mathrm{cur}}=4\mathrm{V}$), 0 V; and (f) PS-TVA mode ($V_{\mathrm{cur}}=4\mathrm{V}$), 16.9 V. The inserted photos are the corresponded cell images observed under crossed polarizers. The red scale bar in the POM images is 50 μm and yellow scale bar in the inserted photos is 5 mm.

Figure 4

Angular-dependent light transmittance ($T$) of TVA mode at different applied voltages: (a) 0 V, (b) 2 V, (c) 3 V, (d) 4 V, (e) 5 V, and (f) 20 V.

Figure 5

Dynamic responses of the TVA and PS-TVA cells: (a) rise time and (b) fall time.

Figure 6

Surface morphologies PS-TVA with different curing voltage (a) 0 V and (b) 4 V curing (threshold voltage before polymerization: 2.15 V).

Figure 7

(a) Tilt angle of TVA mode and (b) twist angle of TVA mode at different applied voltages.

Figure 8

(a) Free energy per unit area. (b) Energy barrier for achieving liquid-crystal director profile at $\mathrm{voltage}=\mathrm{V}$.