Fig. 6: Micro- and macroscopic reflection behavior of Cholesteric Spherical Reflectors (CSRs) polymerized at temperatures of different alignment.

Polymerized, cleaned and dried CSRs are dispersed in NOA160 binder that is photocured into a solid film. POM images are taken in transmission without analyzer (a) and between crossed polarizers (b), and in reflection between crossed polarizers (c, d). The CSRs in a–c have FCD configuration while the CSRs in (d) have tangential alignment. Scale bar in a applies also to b–d. In e–h, macroscopic photos (no polarizers, ambient illumination, black background) of the film with FCD CSRs (left column) compared with the film with tangential CSRs (right column) are shown as a function of viewing angle α with respect to the macroscopic sample normal. Generally, α is different from the local incidence angle θ defined with respect to the helix axis m. The distance between consecutive dashed lines in the top schematic is p/2 and m is everywhere normal to these lines. The large cyan spots in the left sample are due to a few CSR beads dispersed together with the CSR shells. All CSRs in a–h have green retroreflection, while j shows a film with randomly mixed tangential and FCD CSRs with red retroreflection in orthogonal macroscopic view under ambient light, appearing blue-green due to cross communication and inclined illumination. Reflection POM microscopic views of two regions are shown in i and k, revealing the amplified uniqueness of the local reflection pattern. The side length of j is 1 cm.