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.

由胶体二氧化硅颗粒组成的单层组装体，被捕获在空气/水界面上，旨在增强其毛细相互作用。通过同向或异向的胶体表面化学改性，或通过调节亚相表面张力，实现对相互作用强度及其取向特异性的微调。胶体间的毛细吸引力强大且特异性足以驱使颗粒组织偏离平衡，趋向于动态停滞的组装体。对于同向颗粒，在低面积密度下，正方形排列与六边形排列相互竞争，导致其在高密度下的相互挫败，从而形成多晶固体。异向的Janus颗粒因其强烈的吸引力和特定的取向而能够形成最为动态停滞的组装体，尽管在短长度尺度上晶体晶粒高度有序。本研究表明，颗粒的异向表面改性并不总是导致界面处良好的长程有序，尽管它为结构控制开辟了新的可能性。