Cellulose nanocrystals (CNCs) are anisotropic and chiral colloidal nanorods able to self-assemble spontaneously in suspension into a cholesteric phase above a critical concentration. When surfactant-coated CNCs are suspended in apolar solvents such as toluene, their alignment can be controlled using AC electric fields, leading to the gradual unwinding of the cholesteric structure into a paranematic state, whereby all the rods are locally pointing parallel to the external field. <br/>In this talk, we will present the observations of these suspensions when much larger AC electric fields are applied. The suspension was placed in a sealed rectangular glass cell (L: 50 mm, W: 10 mm, T: 1 mm) containing two parallel electrodes used to apply a strong electric field in the width direction. Above a certain electric field threshold that is frequency-dependent, we observe the formation of regular patterns with increasing complexities, distinct from a cholesteric structure, which we ascribe to electrohydrodynamic convection instabilities. To the best of our knowledge, such instabilities were so far only described in molecular nematic liquid crystals.

Electrohydrodynamic convection instabilities in suspensions of cellulose nanocrystals

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