Liquid Crystalline Behavior of Graphene Oxide in theFormation and Deformation of Tough Nanocomposite Hydrogels.

In this paper, we report the formationand transformation of grapheneoxide (GO) liquid crystalline (LC) structures in the synthesis anddeformation of tough GO nanocomposite hydrogels. GO aqueous dispersionsform a nematic LC phase, while the addition of poly(N-vinylpyrrolidone) (PVP) and acrylamide (AAm), which are capableof forming hydrogen bonding with GO nanosheets, shifts the isotropic/nematictransition to a lower volume fraction of GO and enhances the formationof nematic droplets. During the gelation process, a phase separationof the polymers and GO nanosheets is accompanied by the directionalassembly of GO nanosheets, forming large LC tactoids with a radialGO configuration. The shape of the large tactoids evolves from a sphereto a toroid as the tactoids increase in size. Interestingly, duringcyclic uniaxial tensile deformation a reversible LC transition isobserved in the very tough hydrogels. The isolated birefringent domainsand the LC domains in the tactoids in the gels are highly orientedunder a high tensile strain. [ABSTRACT FROM AUTHOR]