Uniform nanomembrane achieves 55 nm pore diameter

A nanomembrane made from block copolymer with pores about 55 nm in diameter has been developed by a research team from the University at Buffalo (UB), USA.

Javid Rzayev (pictured) and Justin Bolton led a team that synthesized a block copolymer nanomembrane, which contains pores >50 nm dia -- a record size for membranes of this kind.

Javid Rzayev (pictured) and Justin Bolton led a team that synthesized a block copolymer nanomembrane, which contains pores >50 nm dia -- a record size for membranes of this kind.

The pore size is the largest anyone has achieved to date using block copolymers, which possess special properties that ensure pores will be evenly spaced, said Javid Rzayev, the UB chemist who led the study. The findings were published online on 31 January 2011 in Nano Letters and will appear in the journal's print edition later this year, with UB chemistry graduate student Justin Bolton as lead author.

"These materials present new opportunities for use as filtration membranes," said Rzayev, assistant professor of chemistry. "Commercial membranes have limitations as far as pore density or uniformity of the pore size. The membranes prepared from block copolymers have a very dense distribution of pores, and the pores are uniform."

"There's a lot of research in this area, but what our research team was able to accomplish is to expand the range of available pores to 50 nanometers in diameter, which was previously unattainable by block-copolymer-based methods," Rzayev continued. "Making pores bigger increases the flow of water, which will translate into cost and time savings. At the same time, 50-100 nm diameter pores are small enough not to allow any bacteria through. So, that is a sweet spot for this kind of application."

The new nanomembrane owes its special qualities to the polymers that scientists used to create it. Block copolymers are made up of two polymers that repel one another but are "stitched" together at one end to form the single copolymer.

When many block copolymers are mixed together, their mutual repulsion leads them to assemble in a regular, alternating pattern. The result of that process, called self-assembly, is a solid nanomembrane comprising two different kinds of polymers.

To create evenly spaced pores in the material, Rzayev and colleagues simply removed one of the polymers. The pores' relatively large size was due to the unique architecture of the original block copolymers, which were made from bottle-brush molecules that resemble round hair brushes, with molecular "bristles" protruding all the way around a molecular backbone.

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