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Abstract
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Self-assembly of colloidal particles into 3D lattices,
with potential applications as single crystals with promising optical
properties, has received considerable attention. The superior
bandgap properties of open colloidal lattices over their more
easily self-assembling close-packed counterparts make them more
demanding for this purpose. However, due to the mechanical
instability of low-coordination open lattices, their self-assembly has
proven to be challenging. Here, we employ a model of triblock
Janus nanoparticles, which includes their surface chemistry
(hydrophobic patches at the poles and surface charges in the
equator) to simulate their self-assembly to three-dimensional
nanocrystals. The solvent is explicitly included in the simulation,
and hydrodynamic interactions are taken into account by dissipative particle dynamics. Biased sampling simulations are conducted to
drive the simulations between different phases. The phase diagrams represent a competition between the liquid phase, open
(pyrochlore, perovskite, and diamond), and close-packed [body-centered cubic (bcc) and face-centered cubic (fcc)] nanocrystals,
whose stabilities depend on the patch width, temperature, and density. Patch widths allowing for three contacts per patch stabilize
the pyrochlore nanocrystal at low densities and the fcc phase at high densities, and those allowing four contacts per patch stabilize
the perovskite nanocrystal at low densities, the bcc lattice at higher densities, and upon further compression, the fcc lattice. The
diamond nanocrystal is stabilized by wide enough patches that provide strong enough bonding between nanoparticles. Increasing the
density converts the diamond nanocrystal to bcc and, subsequently, to a higher-density fcc lattice. The calculated free energies for
conversion of liquid to crystalline phases reveal that the barrier height for nucleation of open lattices (within their stability domains)
is lower than that for denser lattices.
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