From bubbles to capsules

September 07, 2006

Nanocapsules are vessels with diameters in the nanometer range and very thin shells. They can store a tiny volume of liquid and can protect their cargo while transporting it through a foreign medium -- such as a human blood vessel -- without any loss. Further applications for nanocapsules include the encapsulation of scents, printer ink, and adhesives. Once at their destinations, the payloads are released by pressure or friction. Japanese researchers have now developed a clever new technique for the production of silicon dioxide nanocapsules: they start with tiny bubbles of carbon dioxide in a silicon copolymer.

Lei Li and Hideaki Yokoyama coated silicon wafers, which act as a support, with thin films of a special plastic that consists of molecules with segments of different types of polymers, so-called block copolymers, in this case made of polystyrene and silicone. The researchers made their copolymer films such that nanoscopic "droplets" of silicone "float" in a matrix of polystyrene. Supercritical carbon dioxide (CO2) is then forced into this film under high pressure at 60 °C. (In a supercritical fluid, it is impossible to distinguish between the liquid and gas phases.) The CO2 lodges within the droplets of silicone in the block copolymer and forms bubbles. It cannot force its way into the polystyrene matrix, however. In the next step, the scientists cool the film down to 0 °C in order to freeze the polystyrene matrix and then slowly reduce the pressure back to atmospheric levels. The CO2 returns to the gas phase, expands, and escapes from the bubbles without collapsing them. Finally, the researchers expose the polymer film to ozone and UV light. Under these conditions, the polystyrene matrix is completely destroyed; the silicone surrounding the bubbles is oxidized to silicon dioxide (SiO2). This results in a thin film of tightly packed, tiny cavities with a thin shell of silicon dioxide. These nanocapsules have diameters of less than 40 nanometers and walls that are about 2 nanometers wide.

The particular advantage of this method is that the resulting nanocapsules are organized into a two-dimensional structure that can be controlled by varying the segments of the block copolymer.
-end-
Author: Hideaki Yokoyama, National Institute of Advanced Industrial Science and Technology, Tsukuba (Japan)

Title: Nanoscale Silica Capsules Ordered on a Substrate: Oxidation of Nanocellular Thin Films of Poly(styrene-b-dimethylsiloxane)

Angewandte Chemie International Edition 2006, 45, No. 38, doi: 10.1002/anie.200602274

Wiley

Related Polystyrene Articles from Brightsurf:

Scientists develop detector for investigating the sun
Researchers from MIPT have developed a prototype detector of solar particles.

Dynamic membranes set to solve problems of liquid waste treatment
The co-authors, Associate Professor Dinar Fazullin and Associate Professor Gennady Mavrin, have been engaged in the topic of membrane elements for water purification for ten years.

A new species of darkling beetle larvae that degrade plastic
POSTECH Professor Hyung Joon Cha's research team confirms biodegradation of polystyrene using darkling beetle larvae found in Korea.

New platform gauges effects of plastic nanoparticles on human development and health
A study released today in STEM CELLS outlines a new platform researchers designed that allowed them to investigate the potentially harmful effects of microplastics and nanoplastics.

Ion conducting polymer crucial to improving neuromorphic devices
''Neuromorphic'' refers to mimicking the behavior of brain neural cells.

Research in land plants shows nanoplastics accumulating in tissues
As concern grows among environmentalists and consumers about micro- and nanoplastics in the oceans and in seafood, they are increasingly studied in marine environments, say Baoshan Xing at UMass Amherst and colleagues in China.

Polymers can fine-tune attractions between suspended nanocubes
In new research published in EPJ E, researchers demonstrate a high level of control over a type of colloid in which the suspended particles take the form of hollow, nanoscale cubes.

Superworms digest plastic, with help from their bacterial sidekicks
Resembling giant mealworms, superworms (Zophobas atratus) are beetle larvae that are often sold in pet stores as feed for reptiles, fish and birds.

Expandable foam for 3D printing large objects (video)
It's a frustrating limitation of 3D printing: Printed objects must be smaller than the machine making them.

Marine litter in the Bay of Biscay
The scientific journal 'Marine Pollution Bulletin' has just published 'Microplastics in the Bay of Biscay: an overview', a piece of work by the 'Materials+Technologies' research group (GMT) of the Faculty of Engineering - Gipuzkoa.

Read More: Polystyrene News and Polystyrene Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.