Colloidal Superparticles From Artificial Atoms - Molecular Self-Assembly: Advances and Applications - page 415

binding geometry by designing nanocrystal surface functionality,
and thus allows the construction of superparticles with intricate
structures such as binary and ternary superlattices. On the other
hand, the multivalent property makes the interparticle binding
events not exclusive from each other, and allows the co-existence of
multiple binding interactions and geometries inside a superparticle.
Therefore, it is difficult to produce superparticles with long-range
ordered structures.
Fourth, colloidal nanocrystals—the precursor and building blocks
of superparticles—normally exhibit similar surface properties to
those of superparticles.

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It is difficult to design effective ligands to
prevent the fusion and aggregation of colloidal superparticles during
and after synthesis. Indeed, many colloidal superparticle dispersions
are much less stable than colloidal nanocrystal dispersions. In
short, these differences make the synthesis of superparticles more
challenging than the nanocrystal synthesis. A deep understanding
of interparticle interactions is a prerequisite for the successful
synthesis of superparticles, whose size, shape, composition, and
structure must be controlled.

13.1.1 Interactions Between Nanocrystals in Colloidal

Solutions

Superparticle formation is a controlled nanocrystal aggregation. In
this process, colloidal nanocrystals (i.e., the precursor) aggregate
and form superparticles, while the resulting superparticles (i.e., the
product) remain as a stable colloidal dispersion or can form a stable
colloidal dispersion in a chosen solvent. The stability of colloidal
particles is primarily determined by interparticle interactions such
as van der Waals forces between the core parts of two neighboring
nanocrystals, and interactions induced by the surface functionalities
of nanocrystals. These surface interactions include electrostatic

double-charged layer interactions, steric interactions, and
solvophobic interactions. Here, we discuss the nature of these forces
and their potential roles in the formation of superparticles.

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Van der Waals forces include dipole dipole interactions,

induction forces, and London dispersion forces. London dispersion

forces are a major attractive interaction between nanocrystals,
while dipole

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dipole interactions and induction forces appear only
when nanocrystals possess electric dipole moments owing to their