Flexible cholesteric films with super-reflectivity and high stability based on a multi-layer helical structure

Abstract

The growing demand for flexible low-power reflective photonics and display devices has fueled research into high quality flexible materials with super-reflectivity and high stability to environmental influences including broad working temperature ranges and excellent mechanical stress insensitivity. Although tremendous effort has been dedicated towards developing cholesteric film materials with super-reflectivity or high stability, challenges still remain in achieving both due to the existence of liquid crystals that are susceptible and sensitive to external stimuli, such as temperature or mechanical stress. Herein, we fabricate a novel flexible film having super-reflectivity (>80%), a broad working temperature range (−70 °C to 70 °C) and excellent mechanical stress insensitivity (up to 7.88 × 10⁵ Pa) via a “washout–refill–assemble” approach by refilling a polymer (optical adhesive) into a cholesteric film assembled using two cholesteric templates with opposite handedness based on a liquid crystal/reactive mesogen mixture, where no liquid crystals exist in the final fabricated multi-layer film. The all-polymer structure of the film selectively reflects color due to the helical structure of the cholesteric liquid crystals applied in the fabrication procedure of the cholesteric templates with both super-reflectivity and high stability to temperature and mechanical stress. Flexible displays with vivid colors based on proposed films have been demonstrated using the direct printing method on glass and flexible substrates. These materials show great potential for applications such as low-power flexible reflective displays, and other photonic flexible devices including lasers, smart windows, color pixels in digital photographs, and colored cladding of a variety of objects.