Spontaneous formation of liquid crystals in ultralarge graphene oxide dispersions

A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution-phase method involving pre-exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self-assembled brick-like graphene oxide nanostructure can be applied in many areas, such as energy-storage devices and nanocomposites with a high degree of orientation. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of ultralarge graphene oxide sheets (with an aspect ratio of over 30 000) to water above a critical concentration of about 0.1 wt%. Self-assembled, free-standing GO papers with a highly aligned layered structure are fabricated by simple casting of graphene oxide liquid-crystal dispersions.