Twisted,Luxembourg 10-12May2016

Dynamicallycontrollediridescenceofcellulosenanocrystalassemblieswithelectricfield

Bruno Frka-Petesic,1,2 Bruno Jean,1 Laurent Heux*,1 1CERMAV-CNRS, Grenoble, France;

2 Melville laboratory, Dept. of Chemistry, University of Cambridge, Cambridge, UK

Naturalstructuresareoftenmadeofhierarchicallyorganizedassembliesofnanometricelements, with precise functions, like the helicoids in the iridescent beetle shells.Cellulosenanocrystals(CNCs),isolatede.g.bysulphuricacidhydrolysisfromcellulosicfibers,areoneof the typicalmodelofchiralnanorodswithdimensionsof2-50nm indiameter for up to severalmicrons in lengthdependingon their biological origin [1].When dispersed in apolar solvents using surfactants, CNCs spontaneously phase-separateintochiralnematicstructures,butatmuchhigherconcentrationsthaninthosealready observed in aqueous media. The chiral pitch decreases to a few microns,revealingastrongerchiralinteraction[2]andbeautifuliridescentcolorsinsuspension.

Additionally,CNCscanbeorientedbyrelativelymodestelectricfields[3].Recently,wealso showed that these colloids bear a permanent dipole as high as 4000 Debye [4].Combining this orientation featureswith the self-organization properties,we showedthat it is not only possible to orient the cholesteric domains, but also to unwind thecholesteric axis to any desired pitch value as shown by laser light diffraction andiridescence. These spectacular features allow the controlled production of iridescentsubstratewithtailoredproperties,andevenadynamicalcontroloftheorientation.

References[1]S.Elazzouzi,Y.Nishiyama,J.-L.Putaux,L.Heux,etal.Biomac.,9,57–65,2008[2]D.Bordel,J.-L.Putaux,andL.HeuxLangmuir,22,4899–4901,2006[3]S.Elazzouzi,J.-L.PutauxandL.HeuxJ.Phys.Chem.B,113,11069–11075,2009[4]B.Frka-Petesic,B.JeanandL.Heux,EurophysicLetters[1],107280062014[5]B.Frka-Petesic,H.Radavidson,B.Jean&L.HeuxAdv.Mater.,:10.10022017

1a)Iridescence

p/2 p/2 p/2p0/2p0/2

p/2

Cholestericbehaviour

1b)Laserlightdiffraction

1cm

EAC

Laser2θ’

θ1

θ3 GreenRed

θ2 Blue