The dispersion and aggregation of graphene oxide in aqueous media

Abstract

Graphene oxide (GO), as a typical two-dimensional material, possesses a range of oxygen-containing groups and shows surfactant and/or polyelectrolyte-like characteristics. Herein, GO sheets with narrow size distribution were prepared by an ultracentrifugation-based process and the aggregation behaviour of GO in pure water and an electrolyte aqueous solution were studied using laser light scattering (LLS). When adding common electrolytes, such as NaCl and MgCl2, into the GO dispersions, aggregation occurs and irreversible coagulation eventually occurs too. However, the GO dispersion can still remain stable when adding excess AlCl3. The zeta potential of the GO dispersion changes from negative to positive after the addition of access AlCl3, indicating that electrostatic repulsion is still responsible for the dispersion of GO, which is in good agreement with the LLS results. This finding on the dispersion of GO may be applied in the solution processing of GO. It also expands the scope of the design and preparation of new GO-based hybrid materials with different functions.

Graphene and Other 2D Colloids: Liquid Crystals and Macroscopic Fibers

“…Analogy with the twist grain boundary chiral mesophase, a structural model with twisted lamellar structure was proposed for this first chiral mesophase of 2D colloids. Enhancing the ionic strength can screen the electrostatic repulsion and deteriorated the twisted lamellar structure and therefore the optical activity, which testifies that the electrostatic force dominated the GO phase transition . From these experimental result, the electrostatic repulsion between GO sheets boundaries can be deduced as the drive force of the formation of this unique twisted lamellar structure …”

“…A full phase diagram of GO aqueous fluid can be concluded by observation of phase state by tuning the ionic strength. GO dispersion can keep stable in aqueous media due to electrostatic repulsion between negative charges on the planar surface, as revealed from zeta‐potential measurements . The increasing ionic strength and pH brought a screening effect of the electrostatic repulsion (decreasing the Debye length of double electric layer from DLVO theory) and therefore can disturb the stability of GO sheets.…”

Fabrication and characterization of graphene oxide modified polycarboxylic by in situ polymerization

“…Due to some aromatic conjugated structure that has not been oxidized on the GO structure, the GO dispersion solution can present electron absorption spectrum in the UV region, and the dispersion property and dispersion stability of GO solution can be characterized by UV–vis spectrum . According to the Lambert–Beer law, the absorbance is proportional to the concentration of GO, that is to say, it is related to the relative number of GO in the solution .…”

Ultra-Stable Silica Nanoparticles as Nano-Plugging Additive for Shale Exploitation in Harsh Environments

“…However, the downhole environments are very complicated at high salinity ranging from 30,000-317,000 ppm (monovalent ions) and high temperatures of 40-150 • C [10,11]. Many studies demonstrate that the existence of electrolytes made nanoparticles (oxidized MWCNTs) precipitated [12][13][14][15]. High ionic strengths have a strong tendency to make nanoparticles agglomerate due to charge screening, while elevated temperatures disrupt collision probability of particles, eventually leading nanoparticle flocculation.…”