Graphene and related materials such as, for example, graphene nanoribbons hold great promise for applications in a number of technical fields due to their favorable electronic, mechanical and thermal properties. Many of the proposed applications would be facilitated by having available both 1) access to bulk quantities of graphene or graphene nanoribbons and 2) means for forming a high-concentration solution thereof.
Graphene can be produced by manual exfoliation of graphite, although this process is exceedingly low yielding and inefficient. Graphene can also be chemically produced from graphite by oxidation and exfoliation to produce oxidized graphene, followed by chemical or catalytic reduction to reduce the graphene back to near its original state. Although this process is somewhat scalable, the electrical and thermal properties of the reduced graphene generally do not wholly replicate those of unexfoliated graphite. Oxidized or reduced graphenes can also be further chemically functionalized to improve their solubility in conventional organic solvents.
Formation of high-concentration solutions (>a few tens of ppm) of graphene and graphene nanoribbons, even in the presence of surfactants or other dispersants, has not been presently realized. Furthermore, even when a solution can be formed, the graphene or graphene nanoribbons are often not well dispersed as individual particles within the solution. Agglomeration into bulk particles not only hampers dissolution, but it also partially degrades the beneficial structural and electrical properties of these carbon materials. Conventional methods to solubilize carbon materials such as graphene and graphene nanoribbons also typically utilize sonication to facilitate solubilization. Such sonication is typically thought to break apart or otherwise damage graphene and graphene nanoribbon particles, and this method accordingly places an upper limit on particle size that can be attained.
In view of the foregoing, methods to produce high-concentration solutions of graphene and graphene nanoribbons would be beneficial in the art. Such high-concentration solutions would permit ready processing of graphene and graphene nanoribbons into various articles such as, for example, films, fibers, polymer composites and shaped articles containing primarily or solely graphene or graphene nanoribbons. Ideally, such methods would not chemically modify or otherwise damage the graphene or graphene nanoribbons such that the aforementioned beneficial properties of the pristine carbon materials can be maintained.