Colloid

Engineering

Chemical physics

Oxide

Nanoparticle

Metallurgy

Materials science

Graphene

Scattering

Dynamic light scattering

Psychiatry

Particle size

Coagulation

Chemical engineering

Ionic strength

Light scattering

Physical chemistry

Physics

DLVO theory

Nanotechnology

Organic chemistry

Psychology

Optics

Aqueous solution

Dispersion (optics)

Chemistry

Electrode

Electrolyte

Exfoliation joint

Carbon

Graphene oxides (GO) of highly polydisperse size distribution were prepared by the Brodie method and their dispersion stability was characterized. Exfoliation and fractionation led to well-defined particle populations in the Nano, classical Colloidal (submicron) and Micrometer size ranges, as revealed by atomic force microscopy and light scattering measurements. Time-resolved dynamic light scattering experiments revealed that aggregation processes are fully impeded in the intermediate pH regime of 3–13 in the absence of electrolytes. While the resistance against salt-induced aggregation increases with the pH due to the progressive ionization of the surface functional groups of GO sheets, their dispersions are inherently unstable at supramillimolar concentrations of strong acids and submolar concentrations of bases, in line with the DLVO theory. However, the aggregation behavior quantified by the critical coagulation concentrations (CCCs) shows surprisingly substantial platelet size dependence. The CCC of Nano Brodie-GO reaches 360 mm at pH = 12, which is one of the highest values ever reported for GO aqueous dispersions. These results provide useful quantitative information to design processable GO dispersions of pH- and size-tunable stability for future applications.

Size-dependent aggregation of graphene oxide