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Herein, an efficient, facile, scalable production of graphene dispersions via exfoliation of graphite in an environment-friendly PVA/H2O solvent system is reported. To warrant the impact of processing parameters on exfoliation efficiency, a systematic investigation is carried out using UV–visible spectroscopy. Under the optimal shearing parameters (1 h, 10 k rpm) with the PVA-to-fed graphite mass ratio of 10, a high concentration graphene dispersion (3.36 mg mL−1) is achieved. The estimated graphene yield is found to be 33% that further increases to 90% after sediment recycling. With the aim of detailed quality analysis, centrifugal cascading is adopted to predominately sort the graphene flakes from the upper end of the distribution. Through various characterization techniques, it is confirmed that the resulting dispersion comprises high-quality graphene flakes (1–5 layers) having thickness up to 1.48 nm, lateral dimension ranging from 0.3 to 4 µm, and quite a low level of defects (ID/IG = 0.1). The statistical distribution histogram reveals that most flakes are single-layer (41%), including some bi-layer (21%) and tri-layer (28%), while the remaining can be said five or multi-layer graphene. Meanwhile, the efficacy of the PVA/H2O solvent system is also demonstrated using ultrasonic exfoliation, providing a high concentration of graphene (1.1 mg mL−1) in a relatively short time (8 h). Furthermore, the applicability of the PVA-stabilized graphene dispersion is addressed by fabricating various graphene products such as graphene paper electrodes, graphene composites, and graphene thin films. Impressively, the graphene paper electrode imparts an exceptionally high specific capacitance of 199.63 F g−1 in a potential window range of 0 to 2 V, and hence could be a promising alternative to traditional electrodes in supercapacitors. Conclusively, the exfoliation of graphite in a green polymer–solvent system offers to produce highly concentrated graphene dispersions at a minimal cost that could be widely applicable in different research areas, thus holding the potential for commercial viability. [ABSTRACT FROM AUTHOR]

A unified model of grain-boundary segregation kinetics is established, which can simulate the equilibrium and non-equilibrium grain-boundary segregation kinetics during isothermal ageing. The results of model fittings/predictions are in a good consistence with those of the experiments. Values of several important parameters, such as vacancy formation energy, vacancy migration energy, and complex migration energy derived by model fittings, show a reasonably good agreement with those in the references. Relationship between the equilibrium and non-equilibrium grain-boundary segregation mechanisms is discussed in detail. The segregation peak/depletion trough observed in the non-equilibrium segregation kinetics may be ascribed to the vacancy flux. The equilibrium segregation kinetics is considered as a special case in non-equilibrium segregation kinetics with the zero vacancy flux. Both the equilibrium and non-equilibrium segregation kinetics are believed to be dominated by vacancy-solute complex flux. The proposed unified model can be a significant progress in grain-boundary segregation theory, with applications in guiding the design of materials. [ABSTRACT FROM AUTHOR]