Graphene oxide liquid crystal domains: quantification and role in tailoring viscoelastic behavior

Graphene oxide liquid crystals (GOLCs) were exfoliated in a wide variety of solvents (water, ethylene glycol (EG), N-methyl-2-pyrrolidone (NMP), and dimethylformamide (DMF)) by high-speed shearing of graphite oxide. Quantitative polarized light imaging of the equilibrium nematic phases of the lyotropic GOLCs gives insights into the extent of aggregation and quantifiable textural features such as domain size, d. Large nematic domains >100 μm with a high overall degree of order were obtained in water and ethylene glycol, in contrast to 5-50 μm domains in NMP and DMF at comparable volume fractions. Comprehensive rheological studies of these GOLCs indicate that larger domains correlate with higher viscosity and higher elasticity, and scaling analysis shows a power-law dependence of the Ericksen number (Er) with domain size (Er α d^3.09). The improved understanding of the relationship between the microstructure and flow properties of GOLCs leads us to an approach of mixed solvent-based GOLCs as a means to tune viscoelastic properties. We demonstrate this approach for the formation of shear-aligned GOLC films for advanced flexible electronic applications such as all-carbon conductive films and thermal heaters.