Synthesis of spheres with complex structures using hollow latex cages as templates

Hollow latex cages (HLCs) are used as templates to fabricate composite hollow spheres with complex structures. The template HLCs have a polystyrene shell with transverse hydrophilic channels connecting to an interior hydrophilic surface. They are stable and permeable, and a reagent can be preloaded into the cavity reservoir. The interior hydrophilic surface is conducive to a favorable inward synthesis. By simply altering the loading sequence of reagents and their concentration, the morphology of the composite spheres can be tuned. For example, during the formation of titania composite spheres by a sol-gel process using tetrabutyl titanate (TBT), composite hollow spheres with titania pillars protruding from the surface are predominantly created, owing to the formation of titania within the hydrophilic channels when the HLCs, preloaded with water, are immersed into TBT at an appropriate concentration. When the TBT concentration is decreased, the size of the pillars decreases accordingly until they disappear, leading to a smooth outer surface. Conversely, when HLCs loaded with TBT are immersed into water, titania forms only on the interior hydrophilic surface and not within the channels, resulting in composite hollow spheres with smooth outer surfaces. The composite spheres can be further used as templates to grow material on the outer surface, and double-shelled hollow spheres of various compositions are achieved. Macroporous materials with unique morphologies-for example, hollow spheres embedded within the pores-have been derived by using an array template of the composite spheres. The method can be applied to a diversity of inorganic materials, metals, oxides, semiconductors, and functional polymers.