Electrohydrodynamic Convection Instabilities Observed in Suspensions of Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are slender, negatively charged nanoparticles that spontaneously form a cholesteric liquid crystal in aqueous suspension above a critical concentration. When they are suspended in apolar solvents such as toluene using surfactants, the application of an AC electric field leads to the reorientation and then distortion of the cholesteric order until the cholesteric structure completely unwinds into a nematic-like order, typically above 0.4 to 0.6 kV/cm. In this work, we show that at much higher electric fields (\(\ge\)2.4 kV/cm) the sample develops a periodic pattern that varies with the field amplitude and frequency. We ascribed this pattern to electrohydrodynamic convection instabilities. These instabilities usually present complex regimes varying with the field, the voltage, the frequency and the geometry. However, the typical geometry where these instabilities were most documented across the literature differs from the geometry used in this work. This work concludes with possible future experimental investigations to clarify the exact regime of instability responsible for these observations.