Abstract
Colloidal self-assembly is a promising bottom-up route to a wide variety of three-dimensional structures, from clusters to crystals. Programming hierarchical self-assembly of colloidal building blocks, which can give rise to structures ordered at multiple levels to rival biological complexity, poses a multiscale design problem. Here we explore a generic design principle that exploits a hierarchy of interaction strengths and employ this design principle in computer simulations to demonstrate the hierarchical self-assembly of triblock patchy colloidal particles into two distinct colloidal crystals. We obtain cubic diamond and body-centered cubic crystals via distinct clusters of uniform size and shape, namely, tetrahedra and octahedra, respectively. Such a conceptual design framework has the potential to reliably encode hierarchical self-assembly of colloidal particles into a high level of sophistication. Moreover, the design framework underpins a bottom-up route to cubic diamond colloidal crystals, which have remained elusive despite being much sought after for their attractive photonic applications.
Highlights
Colloidal self-assembly is a promising bottom-up route to a wide variety of three-dimensional structures, from clusters to crystals
While hierarchical self-assembly of colloidal particles via small colloidal clusters mimicking the symmetry of molecular structures, i.e., the so-called “colloidal molecules”,11−14 could be a plausible route to structural hierarchy, hierarchical schemes for programmed colloidal self-assembly have been elusive.[4,5]
While the key to the observed structural hierarchy is the hierarchy of patch−patch interaction strengths, the morphology of the colloidal molecules, which essentially serve as the secondary building blocks, is governed by the width of the stronger patch and the range of the patch−patch interactions
Summary
Colloidal self-assembly is a promising bottom-up route to a wide variety of three-dimensional structures, from clusters to crystals. A number of strategies have been explored so far.[21−27] One strategy exploited an interplay between a long-range repulsion and a short-range attraction, both isotropic in nature, at the nanoscale to stabilize a diamond-like open lattice for two oppositely charged nanoparticles.[22] An alternative strategy prescribes the use of anisotropic interactions realized through patchy colloidal particles decorated with four patches in tetrahedral symmetry.[21,24,25] This route faces the challenge of resolving the competition from thermodynamically preferred tetrahedral liquid or gel.[24,25,28] In a related strategy, tetrahedral DNA origami constructs were employed with two types of gold nanoparticles coated with designer single-stranded DNA to form a cubic diamond lattice.[26] in this case the spacing between the nanoparticles in the lattice was considerably larger than the core diameter of the nanoparticles, which could restrict its appeal as a photonic crystal.[27] Another distinct route to open structures, such as the cubic diamond lattice, is to first form a denser lattice with two compositionally distinct species each forming a sublattice, one of which is the cubic diamond lattice as in the case for the MgCu2 Laves phase.[23] The removal of the second sublattice selectively produces the cubic diamond lattice as an open structure This route was followed in a recent work, which employed DNAmediated interactions to guide preassembled tetrahedral colloidal clusters and spheres to form the MgCu2 Laves phase.[27]
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