Orientational rheology of graphene oxide dispersions in isotropic phase, ordered isotropic biphase, and discotic phase
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We present a combined simulation and experimental study of the structure and dynamics of dilute, semi-dilute, and concentrated graphene oxide (GO) aqueous alkaline dispersions. These materials behave as lyotropic systems, with phase ordering as the concentration increases. The sheet spacing in the ordered phases is much broader than that expected by the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Rheological responses in the isotropic phase are similar to rod-like liquid crystals (LCs), which follow the simplified Leslie–Ericksen (LE) model. The dispersions in the biphase and the discotic phase behave similarly to polydomain LC polymers, following the mesoscopic LE model (Larson–Doi (LD) model). The LD model fits the time evolution of shear stress at startup flow, re-startup flow after the cessation of flow, and reversal flow in the discotic phase. Further, the Folgar–Tucker–Lipscomb model fits the stress overshoot in a startup flow, but not the reversal flow.