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Download Spherical confinement of chiral cellulose nanowhiskers
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Spherical confinement of chiral cellulose nanowhiskers Supervisors: Jasper Landman, Andrei Petoukhov & Willem Kegel May 20, 2014 Cellulose nanowhiskers (cellulose nanocrystals, CNCs) are very promising building blocks for sustainable materials in a wide number of applications[1]. Apart from their mechanical properties, such as a very high strength, CNCs can form a socalled chiral nematic phase at sufficient concentration[2], although the mechanism of chirality transfer from the molecular scale to the colloidal scale is not yet fully resolved. It is interesting to see how robust the phase behaviour of CNCs under spherical confinement. We would like to study CNCs inside spherical (double layer) vesicles and see the phase behaviour that arises as the vesicle dimensions become smaller. Moreover, the cellulose inside the vesicles may simultaneously influence the shape of the vesicle Furthermore we would like to solidify the resulting coassemblies to see what optical properties they might have. Not only would they make very interesting micron-sized ‘lenses’, these cellulose spheres may be ideal candidates for 3D spherical lasers, something hitherto only observed in droplets of molecular cholesteric liquid crystals in the liquid phase[3]. We will use a number of in-house techniques such as polarisation and confocal optical microscopy to examine the behaviour of the system at different length scales. In addition, we will use state-of-the-art X-ray scattering and microscopy to study the local structure of nanoparticles inside the droplets. For this we will use the experimental facilities at the ESRF in Grenoble. References [1] S. J. Eichhorn, “Cellulose nanowhiskers: promising materials for advanced applications,” Soft Matter, vol. 7, no. 2, p. 303, 2011. [2] J.-F. Revol, H. Bradford, J. Giasson, R. H. Marchessault, and D. G. Gray, “Helicoidal self-ordering of cellulose microfibrils in aqueous suspension,” Int. J. Biol. Macromol., vol. 14, pp. 170–172, June 1992. [3] M. Humar and I. Muševič, “3D microlasers from self-assembled cholesteric liquid-crystal microdroplets,” Optics Express, vol. 18, no. 26, pp. 111–113, 2010. [4] S. Vignolini, P. J. Rudall, A. V. Rowland, A. Reed, E. Moyroud, R. B. Faden, J. J. Baumberg, B. J. Glover, and U. Steiner, “Pointillist structural color in Pollia fruit,” Proceedings of the National Academy of Sciences of the United States of America, vol. 109, no. 39, pp. 15712–15, 2012. (a) (a,b) A chiral nematic film selectively reflects light of the same circular polarisation as the helicity in the sample. This property is also found in nature, e.g. in the fruits of Pollia condensata[4] (c,d) (b) SEM image of an obliquely cut CNC film, which shows the left-handed helicity into which the individual particles assembled Figure 1 A dried chiral nematic film of CNCs 1 Contact information Jasper Landman H.R. Kruytgebouw, room N709 +31 30 253 3981 [email protected] Andrei Petoukhov H.R. Kruytgebouw, room N703 +31 30 253 1167 [email protected] Student coordinator: Roel Baars [email protected] 2 Willem Kegel H.R. Kruytgebouw, room N711 +31 30 253 2873 [email protected]
