The cover shows a variety of shaped flakes fabricated from polymer cholesteric liquid-crystal material using soft lithography. In work reported by Jacobs and co-workers on p. 217, the micrometer-sized flakes exhibit brilliant circularly polarized selective reflection colors without polarizers or color filters when placed in a fluid-filled electro-optic cell. With the application of a low-magnitude alternating current field, the flakes reorient in hundreds of milliseconds and the colors disappear.
Polymer cholesteric liquid-crystal (PCLC) flakes were investigated for their electro-optical behavior under an applied alternating-current field. Shaped flakes, fabricated using soft lithography and suspended in dielectric-fluid-filled cells, reoriented more uniformly than randomly shaped flakes made by fracturing of PCLC films. Extensive characterization found shaped flakes to be smooth and uniform in size, shape, and thickness. Reorientation in applied fields as low as tens of mVrms μm–1 was fastest for flakes with lateral aspect ratios greater than 1:1, confirming theoretical predictions based on Maxwell–Wagner polarization. Brilliant reflective colors and inherent polarization make shaped PCLC flakes of interest for particle displays.