Assembly of the anisotropic microcapsules in aqueous dispersions

Abstract

The assembly of cubic hollow microcapsules in an aqueous buffer solution had been studied in comparison with the traditional spherical microcapsules with both microcapsules assembled from identical components and having identical surface charges. We observed that the cubic microcapsules mainly form the highly compacted “boxed” clusters with a number of microcubes controlled by ionic strengths in a sharp contrast to the spherical microcapsules for which the random branched chain structures are generally favored. The assembled spherical microcapsules create a large number of openings with extensive internal surface areas while the cubic microcapsules build close, compacted aggregates with densely packed units. The dimensions of the “boxed” clusters from similarly charged cubic microcapsules are greatly stabilized by strong facet-to-facet interactions and can be tuned in a wide range by changing ionic strength. The chain spherical microcapsules are mobile and capable of reconfiguration due to the lower hydrophobic energy of attraction in contrast to compact, stable aggregates of cubic microcapsules. The dramatic differences in assembly of microcapsules with similar nature but different shapes point that the aggregation behavior in such dispersions might be dominated by shape geometry and alternation of facet-to-facet interactions.