Joined: 16 Mar 2004
|Posted: Wed Dec 13, 2006 11:22 am Post subject: Bubbling gas produces nanocapsules
|Bubbling gas produces nanocapsules
by Liz Kalaugher
Researchers at the National Institute of Advanced Industrial Science and Technology in Japan have come up with a new way of creating nanocapsules. The team incorporated bubbles of gas in a block copolymer, which they then treated to leave hollow nanocapsules with silica walls.
The nanocapsules could have applications in drug delivery and for holding perfume, printer ink or adhesives. A key advantage of the technique is that it produces nanocapsules in an ordered 2D arrangement that’s easy to embed in another material. What’s more, the use of a block copolymer means it may be possible to tailor nanocapsule structure by altering the make-up of the copolymer.
To make the nanocapsules the team forced supercritical carbon dioxide under high pressure (20 MPa) at 60°C into a 43 nm thick film of poly(styrene-b-dimethylsiloxane) (PS-PDMS) block copolymer. The copolymer consisted of droplets of PDMS in a polystyrene matrix and was supported on a silicon substrate.
The carbon dioxide entered the CO2-philic PDMS droplets and formed bubbles. The process gave the film a porosity of around 9%. When the scientists cooled the film to 0 °C and reduced the pressure to atmospheric levels, the carbon dioxide returned to the gas phase and escaped from inside the droplets, leaving small voids.
Finally, treatment of the film with ozone and ultraviolet light removed the polystyrene matrix and oxidized the PDMS droplets. This created a thin film of hollow nanocapsules with a silica shell. The nanocapsules were around 30 nm in diameter and had walls roughly 2 nm wide. The capsules were ordered on the substrate with a number density of 7.0 x 1010.
Now the team is investigating the fabrication of more complex structures by using a copolymer with different block fractions.
The researchers reported their work in Angewandte Chemie.
This story was first posted on 20th September 2006.