Cellulose nanocrystals (CNCs) are a sustainable nanomaterial that can be obtained by the acid hydrolysis of bulk cellulose. When an aqueous suspension of CNC is left to dry, films that selectively reflect left-handed circularly polarized light (L-CPL) are formed. This effect is related to the characteristic chiral nematic order that the CNCs assume within the films.

Mark MacLachlan, University of British Columbia, Vancouver, Canada, and colleagues found that films cast from CNC suspensions with particularly high concentrations (≥ 10 wt%) show a quasi-nematic organization – in contrast to the well-known chiral nematic order. The resulting materials effectively depolarize CPL, are transparent, and the simple drop-casting route is practical for a variety of applications.

As an example, the team created a latent image made of quasi-nematic CNC written on a chiral nematic background. Upon observation through circular polarizers, the photonic image is revealed. This shows the method’s promise for novel anticounterfeiting applications.

• Transparent Depolarizing Organic and Inorganic Films for Optics and Sensors,
  Takayuki Hiratani, Wadood Y. Hamad, Mark J. MacLachlan,
  Adv. Mater. 2017.
  DOI: 10.1002/adma.201606083