Coffee ring effect

[9] Control of the substrate temperature was shown to be an effective way to suppress the coffee ring formed by droplets of water-based PEDOT:PSS solution.

The lower-limit size of a coffee ring depends on the time scale competition between the liquid evaporation and the movement of suspended particles.

[16] When the liquid evaporates much faster than the particle movement near a three-phase contact line, a coffee ring cannot be formed successfully.

For suspended particles of size 100 nm, the minimum diameter of the coffee ring structure is found to be 10 μm, or about 10 times smaller than the width of human hair.

[17][18] On porous substrates, the competition among infiltration, particle motion and evaporation of the solvent governs the final deposition morphology.

[20] The transition between these patterns is explained by considering how DLVO interactions such as the electrostatic and Van der Waals forces modify the particle deposition process.

Orientation is afforded by the system trying to reach a state of maximum packing of the particles in the thin meniscus layer over which evaporation occurs.

They showed that tuning the volume fraction of particles in solution will control the specific location along the varying meniscus thickness at which assembly occurs.

[28] Recent advances have increased the application of coffee-ring assembly from colloidal particles to organized patterns of inorganic crystals.