Background: Studies on the formation of colloidal crystals in concentrated suspensions
have mainly been based on dispersed suspensions with a repulsive inter-particle potential of hard or
nearly hard spheres The self-assembly in weakly-flocculated suspensions has still been unrealized.
Here we report on the formation of ordered structures in concentrated suspensions of nearly-hard
spherical particles with weakly-attractive inter-particle interactions that are an order of magnitude
higher than the particles’ thermal energy.
Methods: In our case, the self-assembly in such suspensions is not thermodynamically driven, but an
external shear force must be applied. The driving force for the particles’ ordering is an increase in the
inter-particle interactions. This manifests itself in a decrease in the average angle between the interparticle
interaction direction and the applied shear stress direction.
Results: For a successful ordering into a large-scale closed packed assembly, the external shear force
must not exceed the inter-particle attractive interaction for the minimum possible average angle (as in
the closed packed structures) but be high enough to enable the particles to move in the highly loaded
Conclusions: The developed method for the self-assembly of the weakly flocculated systems can be
applied very generally for e.g. a control over a composition of heterogeneous colloidal crystals, manufacturing
of the large-scale photonic crystals or preparation of very densely packed compacts of particles
needed for the production of sintered ceramics.