Rheological properties of graphene oxide liquid crystal

We report the rheological properties of liquid crystalline graphene oxide (GO) aqueous dispersion. GO dispersions exhibit typical shear thinning behaviors of liquid crystals, which is described by power law or simple Curreau model. Irrespective of the shear rate, shear viscosity exhibits sudden decrease with the increase of GO composition around a critical volume fraction, phi(c)= 0.33%, demonstrating typical colloidal isotropic-nematic phase transition. Dynamic measurements reveal the liquid-like (isotropic phase, G' > G '') behavior at a low GO composition (phi similar to 0.08%) and solid-like (liquid crystalline) behavior at higher compositions (phi similar to 0.45%), where G' exceeds over G ''. Nematic gel-like phase is confirmed at a higher GO composition over > 0.83%, where both G' and G '' moduli are nearly independent of frequency (omega). Simple power law scaling arguments are introduced to model the dependence of yield stress and viscoelastic moduli on the GO composition. We also observed the yield stress and rigidity percolation transition above phase transition composition phi(c) > 0.33% with a percolation exponent of 1.3 +/- 0.1. These rheological insights provide valuable information for the liquid crystalline processing of GO based materials including fibers, sheets and other complex structures for electronic/optoelectronic and energy storage/conversion applications. (C) 2014 Elsevier Ltd. All rights reserved.