Rheological study of highly concentrated aqueous graphene oxide suspensions: the effects of concentration, particle lateral dimensions and number of layers per particle

Aqueous graphene oxide (GO) suspensions have attracted considerable attention due to their unique properties, which can find numerous applications in various fields, from industry to biomedicine. When designing a GO hydrogel for a specific application, a thorough understanding of the effects of appropriate starting material properties and its concentration range on the suspension stability, structural and rheological properties is of essential importance. The present work is concerned with high solids content (from 1.00 to 2.00 w/v%) GO aqueous suspensions exhibiting marked elastic properties. The effects of the GO particles lateral dimensions and the number of GO layers per particle on the flow and viscoelastic properties are investigated. Rheological parameters useful for quantitative interpretation of the results were obtained by fitting the experimental data using Cross, Herschel-Bulkley, and generalized Maxwell models. All GO suspensions showed a marked shear thinning and thixotropic behaviour with a significant yield stress. Their mechanical spectra confirmed viscoelastic behaviour typical for a suspension in an arrested state. Observed differences in values of rheological parameters and their variations with concentration are explained by particle properties and corresponding rotational restrictions, electrostatic attraction/repulsion, nematic phase formation, and particle agglomeration. The research presents fundamental insights into the rheological properties of GO suspensions, which can be manipulated by varying particle geometry and concentration.