C. Meredith, L. Zarzar
Penn State University,
Keywords: structural color, iridescence, microstructures, security features, optical sensors
Summary:Iridescent materials whose brightness and color shift upon changes in viewing or light angles are widely utilized for applications such as overt and covert security features, optical sensors, camouflage and the decoration of consumer products. Color created by iridescent materials doesn’t rely on chemical dyes and pigments, but instead exploits the reflection of light off of geometric structures within a material to generate interference. Typically, iridescent materials utilize diffraction and or thin-film interference mechanisms to produce color, which require formation of nanoscale periodic features on the scale of the 100’s of nanometers. As such, the optical tunability of iridescent materials (e.g. hue/shade, the angular positions and separation of colors) is fundamentally limited by constraints imposed by optical mechanisms relying on nanostructured geometries and materials processing. Here, we introduce a new class of iridescent materials which harness a fundamentally different geometric design and optical mechanism for creating color through interference as light undergoes total-internal-reflection within three-dimensional microstructures on the scale of 10 to 100 microns in size. We show how distinctive, tunable iridescent effects with wide angular color separation are achieved through replicating patterns of microstructures with controllable shape, size, and orientation into a variety of thermoplastic and UV-cured polymeric films.