Invited Article: Chiral optics of helicoidal cellulose nanocrystal films

Abstract

Cellulose nanocrystals (CNCs) in water suspensions behave as lyotropic liquid crystals forming a chiral nematic phase above a critical concentration. Such organization can be retained in solid films and give rise to an intense colored appearance. Here, we fully characterize their optical response by applying optical and scanning electron microscopy, imaging scatterometry and angle-resolved reflectance measurements. We show that the experimental results are well explained by computational modeling using the finite-difference time-domain method, but slightly less well by Berremann’s analytical model.This work was supported by the EPSRC Cambridge NanoDTC [No. EP/G037221/1 to R.M.], the National Centre of Competence in Research “Bio-InspiredMaterials”, the Ambizione program of the Swiss National Science Foundation [No. 168223 to B.D.W.], the European Research Council [No. ERC-2014-STG H2020 639088 to S.V. and A.G.D.], and the BBSRC David Phillips fellowship [No. BB/K014617/1 to S.V.]