Glassy Cholesteric Broadband Reflectors with a Pitch Gradient: Material Design, Optical Properties and Microstructure

Abstract

The cholesteric liquid crystal (CLC) phase may selectively reflect light. The reflection wavelength is correlated with the CLC helical pitch and the wavelength bandwidth δδ with the birefringence. Recent studies have aimed to broaden δδ from several tens - an order of magnitude usually encountered in literature - to several hundreds of nanometers. The latter case would especially be relevant for specific applications such as full-colors displays. Our purpose is to present a novel experimental process to design a CLC with a pitch gradient reflecting light on more than 300 nm. As a novelty, this broadband reflector is a glassy solid. The spectral behaviour is analyzed in parallel to the reflector microstructure which is investigated by transmission electron microscopy for the first time.

Key Words:

• cholesteric liquid crystals
• glassy state
• light reflection
• pitch gradient
• TEM