Expandable graphite (EG) and few-layer graphene (FLG) have proven to be instrumental materials for various applications. The production of EG and FLG has been limited to batch processes using numerous intercalating agents, especially organic acids. In this study, a Taylor-Couette reactor (TCR) setup is used to expand and exfoliate natural graphite and produce a mixture of EG and FLG in aqueous solutions using an amphiphilic dispersant and a semiflexible stabilizer. Laminar Couette flow structure and high shear rates are achieved via the rotation of the outer cylinder while the inner cylinder is still, which circumvents vortex formation because of the suppression of centrifugal forces. Our results reveal that the level of expansion and exfoliation using an aqueous solution and a TCR is comparable to that using commercial EG (CEG) synthesized by intercalating sulfuric acid. More importantly, the resultant EG and FLG flakes are more structurally homogeneous than CEG, the ratio of FLG to EG increases with increasing shearing time, and the produced FLG sheets exhibit large lateral dimensions (>10 μm). The aqueous solutions of EG and FLG are wet-spun to produce ultralight fibers with a bulk density of 0.35 g/cm3. These graphene fibers exhibit a mechanical strength of 0.5 GPa without any modification or thermal treatment, which offers great potential in light-weight composite applications.
Keywords: Taylor−Couette; exfoliation; expansion; fiber; graphene; graphite.