We report a procedure for synthesizing narrow size distribution cube-shaped Co3O4 nanoparticles of controlled size. Viscous and viscoelastic properties of suspensions of the cubes in oligomeric polyethylene glycol (PEG) are investigated at a wide range of particle volume fractions. At high particle fractions, the suspensions manifest complex rheological characteristics, including shear thinning and shear thickening features, which can be tuned by the PEG molecular weight. We discuss these observations in terms of the charge carried by the cubes and the effect of their planar faces on structure formation, break-up, and particle/particle layering.

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