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Hollow Silica Capsules with Well-Defined Asymmetric Windows in the Shell

2012; American Chemical Society; Volume: 28; Issue: 19 Linguagem: Inglês

10.1021/la301560r

1520-5827

Bo Zhao, Maryanne M. Collinson,

Catalytic Processes in Materials Science

A straightforward and effective approach to fabricate porous silica capsules with well-defined asymmetric windows in the shell using raspberry-like templates has been developed. This process begins with the formation of a hierarchical template by chemically coupling a large polystyrene sphere to an ensemble of small, polystyrene latex spheres. The hierarchical template in conjunction with a hard templating method and spin-coating leads to silica capsules with well-defined, asymmetric pores (windows) in the outer shell. Proof-of-principle of this approach has been demonstrated using a 1500/110 nm hierarchical template. The silica capsules thus produced were characterized with scanning electron microscopy and STEM. The diameter of the capsules was ∼1400 nm, and the outer opening of the windows was ∼100 nm in size, consistent with the diameters of the core and satellite spheres considering the shrinkage due to the calcination. The inner opening was ∼30 nm, which gives rise to an asymmetry factor, defined as the diameter of the outer window to the diameter of the inner window, of ∼3. In another example, surface-bound capsules with an asymmetry factor of ∼1 were made. Collectively, these windows can provide efficient pathways to connect the inside of the capsule to the outside and have potential for asymmetric diffusion and rectification.