Capillarity-induced directed self-assembly of patchy hexagram particles at the air–water interface

Abstract

Directed self-assembly can produce ordered or organized superstructures from pre-existing building blocks through pre-programmed interactions. Encoding desired information into building blocks with specific directionality and strength, however, poses a significant challenge for the development of self-assembled superstructures. Here, we demonstrate that controlling the shape and patchiness of particles trapped at the air-water interface can represent a powerful approach for forming ordered macroscopic complex structures through capillary interactions. We designed hexagram particles using a micromolding method that allowed for precise control over the shape and, more importantly, the chemical patchiness of the particles. The assembly behaviors of these hexagram particles at the air-water interface were strongly affected by chemical patchiness. In particular, two-dimensional millimeter-scale ordered structures could be formed by varying the patchiness of the hexagram particles, and we attribute this effect to the delicate balance between the attractive and repulsive interactions among the patchy hexagram particles. Our results provide important clues for encoding information into patchy particles to achieve macroscopic assemblies via a simple molding technique and potentially pave a new pathway for the programmable assembly of particles at the air-water interface.

Self‐assembled Micro‐nanorobots: From Assembly Mechanisms to Applications

“…In the past two decades, researchers used flotation capillary force to assembly not only spherical particles, but also particles with particular shapes, such as ellipsoidal, [57] cubic, [58] hexagram, [59] into MNRs structures. For example, Gary B. Davies and Lorenzo Botto used flotation capillary force to assemble ellipsoidal particles into cluster at the fluid‐fluid interface.…”

“…Kang et al . proposed a strategy to assemble patchy hexagram particles containing hydrophobic vertices and hydrophilic main hexagram bodies into two‐dimensional hexagonal lattice [59] . Although it is not enough for light particles to deform the surface of the water by its own gravity, self‐assembly can also be realized by fabricating surface deformation and producing flotation capillary force under external conditions.…”

A Matter of Size and Placement: Varying the Patch Size of Anisotropic Patchy Colloids

“…The same approach—non-spherical building units provided with a discrete number of bonding sites—can be also applied at the nanometer scale: DNA origami of different shapes have been programmed to assemble into prescribed two-dimensional tilings by taking advantage of blunt end stacking and hybridization sites, thus providing versatile platforms to engineer optical metamaterials and biomimetic tissues [ 18 , 19 , 20 , 21 , 22 ]. At even larger length scales, micrometer non-spherical colloids decorated with attractive spots along their perimeter also form two-dimensional aggregates whose complex geometries can be related to the properties of the constituent units [ 23 , 24 , 25 ]: close-packed versus porous, surface structures, as well as finite clusters with specific architectures can be designed by tailoring the single particle features [ 26 , 27 , 28 , 29 , 30 ]. Colloidal platelets with non-spherical shapes and directional bonding sites—often referred to as patches—constitute an ideal playground for testing and understanding the driving mechanisms of two-dimensional tilings.…”

“…Colloidal platelets with non-spherical shapes and directional bonding sites—often referred to as patches—constitute an ideal playground for testing and understanding the driving mechanisms of two-dimensional tilings. The self-assembly of patchy colloidal platelets is governed by a competition between shape and bonding anisotropy: on the one hand, non-spherical hard shapes tend to maximize edge-to-edge contacts [ 23 , 31 , 32 ]; on the other hand, the presence of attractive patches imposes additional constraints on the assembly process, thus leading to a rich aggregation scenario [ 24 , 25 , 26 ].…”

Ordering Polymer‐Grafted Nanoparticles at Oil–Air Interfaces under Magnetic Fields

“…Such nonequilibrium structures of polymer‐grafted nanoparticles lead to polydispersity in the structures formed . The free energy of polymer‐grafted particles can be easily minimized at interfaces, hence they exhibit a lower surface and interfacial energy relative to linear polymers . The stability of monolayers and increased toughness are attributed to the dense packing of functional groups and chain entanglements between particle arrays …”