Capillarity-driven assembly of colloidal microbullets at an air/water interface

The shape anisotropy of colloids controls interparticle interactions at fluid interfaces, hence governing colloidal assembly. The preferred orientation of rod-like particles at flat interfaces is dependent on the specific particle shape, aspect ratio, and contact angles.

Anisotropic bullet-shaped colloids are studied at an air/water interface with optical microscopy. The fractal dimension, as well as positional and orientational orders, are characterized. The deformation of the interface around a microbullet is evaluated.

The pronounced asymmetric interface distortion around microbullets leads to a strong capillary attraction. This attraction is dependent on orientation and results in preferred lateral particle interactions. A series of laterally aligned microbullets form smectic-like domains that subsequently attract each other, resulting in the development of a rigid gel-like monolayer. The arrangement of this monolayer strongly resembles a smectic-like order at short distances, while exhibiting disorder attributed to different domain orientations at larger distances.