Journal
CELLULOSE
Volume 22, Issue 2, Pages 1103-1107Publisher
SPRINGER
DOI: 10.1007/s10570-015-0569-3
Keywords
Cellulose nanocrystals; Iridescent films; Chiral nematic structure; Coffee-stain effect; Film topology and color
Funding
- Natural Sciences and Engineering Research Council Canada
- Fonds Quebecois de la Recherche sur la Nature et les Technologies through the Center for Self-Assembled Chemical Structures
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Films prepared from aqueous suspensions of cellulose nanocrystals (CNC) often display iridescent colors due to the reflection of light from the helicoidal orientation of the rod-like CNC in the film. Droplets of CNC suspension deposited on a plane surface evaporate to give films that display iridescent rings. Profilometry measurements across the rings show that the outer edge of the films is much thicker than the region in the center. This is ascribed to a coffee-stain effect; the CNC are transported to the outer edge for droplets where the contact line is pinned during evaporation. The gradient in concentration across the ring results in a color gradient, with the longer wavelengths decreasing towards the center of the sample, in accord with the hypothesis of a two-stage process for CNC chiral nematic color formation.
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