Graphene Oxide Takes the Helm: Carbon Particles Rewrite the Rules of Emulsion Stability

Emulsions are everywhere in modern life, from the mayonnaise in a kitchen to the latex in a paint can, yet keeping oil and water from separating remains one of chemistry’s most persistent challenges. For more than a century, the dominant solution has been surfactants, molecules that wedge themselves at the boundary between oil droplets and water to keep them apart. But a quieter revolution has been gathering pace. Instead of molecules, tiny solid particles can be deployed to armor each droplet, forming a physical shell that resists coalescence far more stubbornly than any conventional surfactant. These so-called Pickering emulsions, first described independently by Ramsden in 1904 and Pickering in 1907, have exploded in popularity over the past two decades, and a new review published in Frontiers in Soft Matter by researchers at the Centro de Investigación en Química Aplicada in Saltillo, Mexico, maps out why carbon-rich particles, above all graphene oxide, have become the stars of this field.

The numbers tell a striking story. A Scopus search for publications on Pickering emulsions shows year-on-year growth since 2000, peaking at 1,366 papers in 2025. The appeal is easy to understand: Pickering emulsions are simple to prepare, remarkably stable, and versatile across applications ranging from catalysis and filtration membranes to drug delivery, antibacterial coatings, cosmetics, nutraceuticals, and food technology. What the Mexican team, Miguel Rosales-Guzmán, María Esther Treviño Martínez, and Enrique Saldívar-Guerra, add to this crowded literature is a dual focus that has been largely missing until now. Their review concentrates specifically on stabilizers drawn from carbon allotropes and carbon-rich materials, and it devotes unusual attention to emulsion polymerization, the industrial workhorse process in which monomers are polymerized inside emulsion droplets to produce the latexes behind countless commercial and high-tech polymers.

The physics underlying Pickering stabilization is elegant. Solid particles that are partially wetted by both oil and water lodge themselves at the oil-water interface, where they form a mechanical barrier. The decisive parameter is the three-phase contact angle at the point where particle meets interface. If that angle is below 90 degrees, the particle is more hydrophilic and favors oil-in-water emulsions; above 90 degrees, it is more hydrophobic and favors water-in-oil systems. If a particle is completely wetted by either phase, stabilization fails entirely. Crucially, the energy required to rip a particle off the interface is typically far higher than thermal energy, which is why Pickering emulsions can be dramatically more stable than their surfactant-stabilized cousins. For spherical particles, this detachment energy scales with the square of the particle radius and the interfacial tension, and analogous expressions exist for disk-like and rod-shaped particles, geometries that matter greatly when the stabilizers are flat graphene sheets.

That is where graphene oxide enters the picture. Pristine graphene and carbon nanotubes are stubbornly hydrophobic, but oxidizing graphite to graphene oxide grafts hydroxyl and epoxy groups across the planar surface and carboxyl groups mainly at the flake edges. The result is a material that is broadly hydrophilic with localized hydrophobic zones, an inherently amphiphilic character that makes it naturally suited to stabilizing oil-in-water emulsions. Even better, those oxygen-bearing functional groups are chemical handles: researchers can attach hydrophobic alkyl amines, polymers, surfactants, or inorganic nanoparticles to tune the wettability for whatever emulsion type a given application demands. The review highlights how the degree of oxidation itself shifts the contact angle, with reported values of 63.6, 55.8, and 90.6 degrees corresponding to different oxygen-to-carbon ratios, giving formulators a dial they can turn.

The functionalization toolbox is impressively broad. A redox reaction between graphene oxide and ferrous ions decorates the sheets with magnetic iron oxide nanoparticles, while treatment with chloroauric acid yields gold-decorated hybrids. One-pot hydrothermal routes can simultaneously reduce graphene oxide to graphene and graft amine groups from polyacryloyl hydrazide, producing stabilizers for olive oil and n-decane emulsions. Ball milling offers a scalable alternative, and pyrolyzing citric acid at 200 degrees Celsius in air generates hydrophilic graphene quantum dots just nanometers across, which can then be functionalized with amines to stabilize dodecane-in-water emulsions or with histidine for styrene-in-water systems. Carbon nanotubes, meanwhile, can be tamed with oxygen plasma or nitric acid oxidation. Selective modification can even produce Janus particles with two chemically distinct faces, an asymmetry prized for interfacial work.

The most conceptually intriguing section of the review concerns polymerization inside graphene oxide-stabilized emulsions. In conventional emulsion polymerization, water-soluble initiators generate radicals that enter monomer-swollen particles, and the compartmentalization of radicals, at most one per particle at any time, governs the kinetics and molecular weights. But in the reported graphene oxide systems, the initiator of choice has been AIBN, which dissolves in the organic phase, hinting that the mechanism may resemble miniemulsion polymerization instead. The large graphene oxide platelets cloaking each droplet may also impede radical exchange between phases. The authors are candid that the mechanism remains an open question, noting that most published studies vary only one or two parameters and use inconsistent emulsion preparation methods, making firm conclusions impossible. What is clear is that the approach works: polystyrene microspheres sheathed in graphene oxide platelets have been produced since the end of the first decade of this century, and polymerizations have focused mainly on styrene and methyl methacrylate.

The applications catalogued in the review read like a tour of modern materials science. Phase-change materials such as paraffins can be encapsulated with extraordinary efficiency; one system using 7.4 weight percent graphene oxide achieved 100 percent encapsulation and a thermal conductivity of 1.3 watts per meter-kelvin for personal thermal management textiles. Self-healing coatings exploit graphene oxide microcapsules that rupture to release healing agents, with one epoxy system reducing concrete’s capillary water absorption by 98.3 percent. Freeze-drying emulsions yields porous aerogels for pressure sensors, electromagnetic interference shielding composites reach 41.4 decibels of shielding effectiveness, catalytic desulfurization systems remove 97 percent of sulfur from fuel oil, and graphene oxide quantum dots have even served as adjuvants boosting immune responses to a Chlamydia trachomatis vaccine. Each droplet can act as a nanoreactor, as demonstrated by the synthesis of 2-aminothiazole with isolated yields of 85 to 90 percent.

Among carbon-based stabilizers, the hierarchy is unambiguous. Graphene oxide dominates, accounting for more than 75 percent of recent literature entries, followed by other graphene derivatives, carbon nanotubes, and carbon quantum dots. The reasons are practical: graphene oxide is comparatively easy to prepare, inherently amphiphilic, and endlessly modifiable. Carbon nanotubes, despite their industrial maturity driven largely by lithium-ion battery electrodes, are harder to synthesize reproducibly and require more elaborate chemistry to become amphiphilic. Production costs for graphene derivatives and nanotubes remain relatively high but are expected to fall over the next five to ten years as volumes increase, and because these stabilizers are used in small proportions, cost may not be prohibitive for many emulsion applications.

Challenges remain, and the review does not shy away from them. The single greatest obstacle to real-world deployment is scaling up graphene oxide production so that the material performs reproducibly as a stabilizer, since current processes suffer significant batch-to-batch variability. Toxicity is another open question: carbon nanomaterials show varying toxicity depending on dimensions, surface modification, and purity, with nanotubes appearing potentially more harmful than graphene derivatives, though surface modification seems to attenuate the risk. The environmental fate of these materials at end of life has been largely overlooked. The authors argue that future research must pivot from proof-of-concept toward practical implementation, with attention to scalability, efficiency, and recyclability, and that unraveling the polymerization mechanism and the self-assembly processes that govern final material properties will require systematic studies across monomer types, oxidation degrees, sheet sizes, and temperatures. For a field that grew from a century-old curiosity into a 1,366-papers-a-year enterprise, the next chapter will be written not in the laboratory alone but in the pilot plant.

Subject of Research: Pickering emulsions stabilized by graphene oxide and other carbon-rich particles, including their use in emulsion polymerization and applications

Article Title: Pickering emulsions: emulsion polymerization and systems stabilized with carbon allotropes or carbon-rich materials

Article References: Rosales-Guzmán, M., Treviño Martínez, M. E., & Saldívar-Guerra, E. (2026). Pickering emulsions: emulsion polymerization and systems stabilized with carbon allotropes or carbon-rich materials. Frontiers in Soft Matter, 6, Article 1908524. https://doi.org/10.3389/frsfm.2026.1908524

Image Credits: AI Generated

DOI: 10.3389/frsfm.2026.1908524

Keywords: Pickering emulsions, graphene oxide, emulsion polymerization, carbon nanotubes, graphene quantum dots, colloids, interfacial science, phase change materials, self-healing coatings, aerogels, drug delivery, nanomaterials