For a special issue of ChemPhysChem on the physical properties and behaviour of liquid crystals, we published a study on how the orientation and pitch of the helix in films formed by drying cholesteric liquid crystalline suspensions of cellulose nanocrystals (CNC) can be controlled with high accuracy based on a few simple considerations. The first point is that tactic boundaries, always present if one starts with suspensions that are in the phase coexistence regime, randomize the orientation of the helix, thereby giving rise to the irregular mosaic texture (left) often seen when drying films from low concentration CNC suspensions. By simply raising the concentration such that the initial suspension is fully liquid crystalline, a film with uniformly standing helix and much more uniform pitch can be achieved (right). Moreover, we show that an orbital shear flow can have a good effect in orienting the helix even when tactoids cannot be avoided. The work is a collaboration with the LC Nano lab of Prof. Giusy Scalia and the group of Prof. Lennart Bergström at the Materials and Environmental Chemistry Department of Stockholm University. You can find the paper at the ChemPhysChem web site here. Unfortunately, we could not include color images in the final version of the paper, so be sure to also download the Supporting Information file, which contains all images in color version (the color is important for the discussion).

Note: if you want to learn more about liquid crystals from CNC, please check out our recent review article (open access!) in NPG Asia Materials.

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