Large-Scale Self-Assembly in Weakly-Flocculated Suspensions

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 suspension. Conclusion: The developed method for the self-assembly of the weakly flocculated systems can be applied very generally 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.