Hollow Silica Shells

Hollow silica shells are prepared by over-coating µ-Sq beads with a liquid silicon precursor. The beads then act as a sacrificial template being removed by thermal degradation to leave hollow silica particles.

They appear white in colour, although the shell walls are both colourless and transparent; consist of amorphous silica, and have perforations in the shell walls that allow the shells to ‘contain’ molecules within the shell void.

Hollow silica shells have been developed as carriers for chemical additives in industrial, pharmaceutical and cosmetic applications.

Physical properties:

Physical State: Solid
Colour:White
Odour:None reported
Solubility in Water:Insoluble
Specific Gravity/Density:1.3 - 1.6 g.cm^-3
Decomposition Temperature:>1400°C

Particle size (diameter) range:0.65 – 2.0 µm
Average particle size:0.94 ± 0.01 µm

Shell wall thickness:≥10% shell diameter

Mean nominal rupture stress:438 ± 47 MPa
Mean deformation at rupture:+ 53% initial diameter

Surface area (using BET):>370 m²/g

Chemical Formula:

Contains Si, O (>99.8% SiO₂)

Additional information:

Hollow silica shells are prepared and supplied as aggregated clusters in a dry powder. Aggregate size distribution is shown below.

The silica in the Hollow silica shells is completely amorphous, as indicated by the following x-ray powder diffraction pattern.

The silica in the walls of the Hollow silica shells is transparent so any coloured material contained inside the shells will be seen through the shell walls, as demonstrated here with shells filled with a range of organic dyes.

Proof that the inner void space of the shells can be accessed is demonstrated in the following image, which is the cross-section of a shell that had been filled with 16 nm diameter gold nanoparticles.

Picture courtesy of Prof. Jon Preece, Birmingham University

Publications:

Shakiela Begum, Ian P. Jones, Chengge Jiao, Daniel E. Lynch and Jon A. Preece, “Characterisation of hollow Russian doll microspheres”, J. Mater. Sci., 2010, 45, 3697-3706.

Daniel E. Lynch, Yasser Nawaz and Thor Bostrom, “The Preparation of Sub-Micrometer Silica Shells using Poly(1-methylpyrrol-2-ylsquaraine)”, Langmuir, 2005, 21, 6572-6575.

Eskender Mume, Daniel E. Lynch, Akira Uedono and Suzanne V. Smith, “Investigating the binding properties of porous drug delivery systems using nuclear sensors (radiotracers) and positron annihilation lifetime spectroscopy — Predicting conditions for optimum performance”, Dalton Trans., 2011, 40, 6278-6288.

Shakiela Begum, Ian P. Jones, Daniel E. Lynch and Jon A. Preece, “One-step deposition of Au nanoparticles onto chemically modified ceramic hollow spheres via self-assembly”, J. Exper. Nanoscience , 2011. DOI: 10.1080/17458081003752962