Out-of-Equilibrium Assembly of Colloidal Particles at Air/Water Interface Tuned by Their Chemical Modification

Assemblies of monolayers made of colloidal silica particles trapped at the air/water interface are prepared to have an increasing capillary interaction. Fine-tuning of the strength of interaction and its orientational specificity is achieved through isotropic or anisotropic colloid surface chemical modification or by adjusting the subphase surface tension. The capillary attraction between colloids is strong and specific enough to drive the particle organization out of equilibrium toward kinetically arrested assemblies. For isotropic particles, the square order competes with the hexagonal one at low area densities, which leads to their mutual frustration resulting in a polycrystalline solid at high densities. Anisotropic Janus particles attract so strongly and with such an orientational specificity that the resulting assemblies are the most dynamically arrested, although the crystal grains are highly ordered on the short length scale. We show that the particle anisotropic surface modification does not always result in a good long-range ordering at interfaces, although it opens up new possibilities of structure control.