Suppressed twist in droplets of cholesteric rod-like virus as identified by single particle imaging

The director field configuration of a colloidal chiral nematic liquid crystal confined in droplets is studied in this work. We employ microfluidics to produce monodisperse droplets containing nematic dispersions of fd virus surrounded by a carrier oil phase, while we vary the size of the droplet as well as the concentration of the virus. The resulting director fields within the droplets are studied at the single-molecule level, using confocal microscopy. The 3-D structures are linked to polarisation microscopy observations of bright rings, which can be attributed to a cholesteric twist of the director field. We identify boundaries of concentration and size where one and two rings are observed, suggesting suppression of the cholesteric twist by confinement. Single particle confocal observations confirm that indeed the twist in the director field underlies the ring formation, but they also show that the twist is non-monotonous throughout the droplet and much smaller than observed in bulk