Directed self-assembly of a colloidal kagome lattice

Abstract

A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering and the design of porous materials, this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties, but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal-in this case a colloidal kagome lattice-through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres. This open network is of interest for several theoretical reasons. With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks.

Colloids with valence and specific directional bonding

“…Their diversity in particle number and symmetry is translated directly to the number and symmetry of the particle patches. In contrast to the planar symmetry of Janus particles 23,33 , the symmetries of these patchy particles are fully 3-dimensional. Supplementary Fig.…”

“…For example, so-called Janus particles with asymmetrically functionalized surfaces can be made, but normally have only a single patch [20][21][22] . Triblock Janus particles have also been fabricated by glancing-angle deposition and assembled into a kagome lattice, the 2-dimensional analogue of a diamond crystal 23 . However, only two patches are made using this method, and low quantities of particles are obtained.…”

A colloidoscope of colloid-based porous materials and their uses

“…32,33 The composition can later be tailored as desired, as discussed below and described in Figure 2. With the focus on the assembly of simple, spherical particles, this review does not cover the synthesis and self-assembly of more complex colloidal building blocks, such as Janus particles, 34,35 patchy particles, [36][37][38][39] core-shell particles, [40][41][42] particles with more complex internal structures, [43][44][45] anisotropic particles, 46 or non-spherical nanocrystals. [47][48][49][50] Complex properties and highly functional materials can emerge solely by controlling the structure of the material or by providing a template to generate patterns in another material.…”

Porous polymer particles—A comprehensive guide to synthesis, characterization, functionalization and applications

“…pH of the medium is also important: a carboxylic acid particle will not be charged at low pH. Adding a salt to the medium also suppresses particle charge [289]. Finally, surface charge can be induced by adding anionic surfactants to the medium, forming a charged polymer layer around the particles.…”

“…In this range, a high surface charge will help the formation of more stable dispersions of particles in a liquid medium. Oppositely, surface charge is not desired for self-assembly purposes [289]. Charged particles are generally obtained by using acid [50] or base [191] monomers, yielding negative or positive charge, respectively.…”