Fabrication of Hollow Silica Microspheres with Orderly Hemispherical Protrusions and Capability for Heat-Induced Controlled Cracking

Abstract

Hollow silica microspheres with orderly protrusions on their outer and inner surfaces were fabricated in three simple steps: (1) suspension polymerization of a polymerizable monomer containing silica nanoparticles to obtain polymeric microspheres with a layered shell of silica particles; (2) sol-gel reaction of tetraethoxysilane (TEOS) on the surface of the microspheres to connect the silica nanoparticles; (3) removal of polymer core by calcination. The shell composed of silica-connected silica nanoparticles remained spherical even after calcination, and the characteristic surface morphology with protrusions were obtained on both inner and outer surfaces. Measurements of the mechanical strength revealed that the compression modulus of the hollow microspheres increased with increasing thickness of the silica layer, which could be controlled by changing the concentration of TEOS in the sol-gel reaction. Rapid heating of the hollow silica microspheres with the thin silica-connected layer led to silica shell cracking, and the cracks were mostly observed in the connecting layer between the silica nanoparticles. The stress was probably concentrated in the connecting layer because of its lower thickness than the nanoparticles. Such characteristic of the hollow microspheres is useful for a capsule with capability for heat-induced controlled cracking caused by internal pressure changes.

Hollow Silica Nano and Micro Spheres with Polystyrene Templating: A Mini-Review

“…It is also possible to introduce silica particles on PS during the synthesis of the PS sphere. M. Takafuji et al [ 107 ] synthesised hollow silica microspheres using a template made from PS and silica nanoparticles modified with 3-methacryloxypropyl trimethoxisilane (M). M molecules were grafted to silica nanoparticles (MSiN) and mixed in an emulsion of styrene, EGDMA (ethylene glycol dimethylacrylate), AIBN, PVA, and water.…”

“… SEM images of the coated MSiNPS at different TEOS volume. ( a ) No TEOS, only MSiNPS, ( b ) 0.04 mol/L, ( c ) 0.08 mol/L, ( d ) 0.16 mol/L, ( e ) 0.32 mol/L, ( f ) 0.48 mol/L [ 107 ]. …”

Architectural Design of Self‐Assembled Hollow Superstructures

“…A carbon coating layer was derived from the carbonification of ligands composed of OA molecules belonging to either the template channel surface or the building block surface . Additionally, an SiO 2 shell can easily and conveniently employed be used as an additional interfacial component, as demonstrated by Ihara et al, to fabricate hollow SiO 2 microspheres coated by SiO 2 nanoparticles and a SiO 2 ‐connected layer ( Figure ) . The resultant self‐assembled SiO 2 superstructures were stabilized by a chemical cross‐linking SiO 2 layer that was generated via a sol–gel reaction in the silanol groups on the layered SiO 2 nanoparticle shell.…”

“…Strategy for the fabrication of hollow microspheres with orderly protrusions on the outer and inner surfaces. Reproduced with permission . Copyright 2017, American Chemical Society.…”