Controlling supraparticle shape and structure by tuning colloidal interactions.

Hypothesis: Assembly of colloids in drying colloidal suspensions on superhydrophobic surface is influenced by the colloidal interactions, which determine the shape and interior structure of the assembled supraparticle. The introduction of salt (electrolyte) into the assembly system is expected to influence the colloid interactions and packing during the evaporation process. Hence, both the outer shape and internal structure of supraparticles should be controlled by varying salt concentrations.

Experiments: Suspensions of electrostatically stabilized polystyrene particles with specified salt concentrations were chosen as model systems to conduct the evaporation on a superhydrophobic surface. A systematic study was performed by regulating the concentration and valency of salt. The morphology and interior of supraparticles were carefully characterized with electron scanning microscopy, while the colloidal interaction was established using colloidal probe atomic force microscopy.

Findings: Supraparticles displayed a spherical-to-nonspherical shape change due to the addition of salts. The extent of crystallization depended on salt concentration. These changes in shape and structure were correlated with salt-dependent single colloid interaction forces, which were not previously investigated in detail in radially symmetric evaporation geometry. Our findings are crucial for understanding assembly behavior during the drying process and offer guidance for preparing complex supraparticles to meet specific applications requirement.