The slow evaporation of suspensions of cellulose nanocrystals (CNCs) yields solid films with a cholesteric nanostructure. These materials are iridescent and exclusively reflect left circularly polarized (LCP) light, due to their helicoidal assembly.
Maria H. Godinho, Universidade NOVA de Lisboa, Caparica, Portugal, and colleagues have prepared a new CNC sandwich material which also reflects right circularly polarized light (RCP). Naturally occurring defects (gaps) in the cholesteric structure of CNC films were impregnated with the nematic liquid crystal 5CB. The resulting nematic 5CB layer, sandwiched between two left-handed cholesteric CNC domains (pictured), works like a half-wave retardation plate.
In the obtained photonic films, both LCP and RCP light are simultaneously reflected. The reflection of RCP showed dependence on an applied electric field or a change of temperature. According to the researchers, the sustainability of cellulose and the ease of preparation could make this method useful for advanced photonic devices.
- Mind the Microgap in Iridescent Cellulose Nanocrystal Films,
Susete N. Fernandes, Pedro L. Almeida, Nuno Monge, Luis E. Aguirre, Dennys Reis, Cristiano L. P. de Oliveira, António M. F. Neto, Pawel Pieranski, Maria H. Godinho,
Adv. Mater. 2016.