Abstract
Commercialization of graphene based applications inevitably requires cost effective mass production. From the early days of research on graphene, direct liquid phase exfoliation (LPE) of graphite has been considered as the most promising strategy to produce high-quality mono or few-layer graphene sheets in solvent dispersion forms. Substantial success has been achieved thus far in the LPE of graphene employing numerous solvent systems and suitable surfactants. This invited review article principally showcase the recent research progress as well as shortcomings of surfactant assisted LPE of graphene. In particular, a comprehensive assessment of the quality and yield of the graphene sheets produced by different categories of the surfactants are summarized. Future direction of LPE methods is also proposed for the eventual success of commercial applications.
Highlights
Commercialization of graphene based applications inevitably requires cost effective mass production
4 Conclusion and outlook It is well-recognized that one critical bottleneck standing in front of commercial utilization of graphene is the lack of a reliable mass production method for high quality graphene
liquid phase exfoliation (LPE) of graphene was initially developed with specific surface energy matching solvents
Summary
2.1 Dispersing medium : solvent In an LPE recipe, solvent is the most important factor dominating the overall productivity of exfoliation. An ideal solvent should be able to effectively overcome the van der Waals interaction between the graphene layers held within a π-π stacking distance of 3.35-3.4 Å. In the presence of a solvent, the potential energy between the adjacent layers given by the dispersive London forces becomes significantly reduced. Coleman et al proposed that when the refractive index of solvent matches with that of graphene, this potential energy can even approach zero. They demonstrated that solvents with interfacial tension (γ) around ~41 mJm−2 is desired to minimize the energy input in attaining effective separation of sheets beyond the range of the strong van der Waals forces [19]. An approximate expression from a thermodynamic perspective was provided to account for their experimental results as given below
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