Liquid Crystalline Microdroplets of Graphene Oxide via Microfluidics

Study of stable liquid crystal (LC) microdroplets is of great significance for LC dynamics in confined space or at topological surface. However, the fabrication of LC microdroplets with diverse shape without ionic gelation agents still remains challenging due to the fluid instability. Here, we utilize the microfluidic technology to prepare graphene oxide (GO) LC microdroplets with various morphologies based on the anomalous rheological property of GO aqueous dispersion. Different from LC of one-dimensional polymer, LC containing two-dimensional GO sheets exhibits considerable viscoelasticity and weak extensibility, resulting from the planar molecular conformation and the absence of intermolecular entanglements. The low extensibility ensures that GO aqueous suspension is discretized into monodispersed microdroplets rather than thin thread in the microfluidic channels. The large viscoelasticity and ultra-long relaxation time of GO LC enable the diverse stable morphologies of microdroplets. The droplet morphology is well controlled from sphere to teardrop by modulating the competition between GO viscoelasticity and interfacial tension. The two-dimensional GO LC featuring unique rheological property provides a novel system for the microfluidic field, and corresponding topological stability enriches the LC dynamics and opens a new pathway for designing graphene-based materials.