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.