From Coffee Rings to Saucer Patterns: Graphene Oxide’s Role in Shaping Droplet Deposits

Graphene oxide droplet patterns

We’ve all seen it—a dried coffee drop leaves behind a dark, ring-like stain. This phenomenon, known as the coffee-ring effect, is a common occurrence in evaporating droplets, where particles migrate toward the edges, leaving a dense peripheral residue. But what if we could control this process? A new study reveals that graphene oxide’s surface chemistry might hold the key to transforming these rings into smooth, uniform films, unlocking potential for advanced coatings, printable electronics, and more.

In their research published in Langmuir, scientists explored how graphene-based materials like graphene oxide (GO) and reduced graphene oxide (rGO) behave in drying droplets. The results highlight a fascinating interplay between chemistry, physics, and nanomaterials engineering, paving the way for eco-friendly innovations in material science.

The Coffee-Ring Challenge

For industries such as inkjet printing and functional coatings, the coffee-ring effect is more than a curiosity—it’s an obstacle. A uniform coating is often critical for applications in electronics, biosensors, and energy devices. When colloidal particles deposit unevenly, it compromises the performance and aesthetic quality of the final product.

Graphene and its derivatives, renowned for their exceptional electrical, thermal, and mechanical properties, are central to many cutting-edge technologies. However, understanding how these quasi-2D materials behave during droplet evaporation has remained an underexplored domain—until now.

Graphene Oxide vs. Reduced Graphene Oxide

The team investigated droplets containing rGO and GO to see how surface chemistry influences deposition patterns. While rGO, which has a lower oxygen content and more graphitic structure, produced the familiar coffee-ring deposits, GO behaved quite differently. Instead of rings, the researchers observed uniform, saucer-shaped films covering the entire droplet footprint.

This surprising behavior is attributed to GO’s amphiphilic nature, which arises from its mix of hydrophilic oxygen-rich functional groups (like hydroxyl and carboxyl) and hydrophobic graphitic domains. These properties drive GO sheets to self-assemble at the liquid-vapor interface, aligning and stabilizing to create an even coating as evaporation proceeds.

A Green Chemistry Bonus

In a nod to sustainability, the researchers also demonstrated a green synthesis route for rGO using Acacia concinna seed extract. This eco-friendly method performed comparably to traditional hydrazine-based processes but without toxic chemicals. Interestingly, the deposition behavior still followed the same pattern, reinforcing the idea that it’s the oxygen content—not the synthesis route—that dictates droplet deposition outcomes.

Implications for Materials Science

This research opens exciting possibilities for fine-tuning material deposition in applications ranging from nanoelectronics to biomedical devices. By manipulating the surface chemistry of graphene-based materials, scientists could design predictable, uniform coatings that enhance device performance and enable new manufacturing techniques.

Read the full article here: https://phys.org/news/2025-07-coffee-saucer-patterns-graphene-oxide.html

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