Materials

New polymer may find use in electronically-switchable filters

New polymer may find use in el...
Johannes Gladisch works with a conductive carbon fiber that's been coated with the polymer
Johannes Gladisch works with a conductive carbon fiber that's been coated with the polymer
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A carbon fiber coated with the polymer, the latter seen here as a solid (top) and a gel (bottom)
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A carbon fiber coated with the polymer, the latter seen here as a solid (top) and a gel (bottom)
Johannes Gladisch works with a conductive carbon fiber that's been coated with the polymer
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Johannes Gladisch works with a conductive carbon fiber that's been coated with the polymer

It certainly would be handy if there was a filtration medium that could be electronically "switched" to capture particles of different sizes. It turns out that there soon may be, thanks to a newly-developed conductive polymer that changes state, on demand.

Created by scientists at Sweden's Linkoping University – working with colleagues at Imperial College London – the material ordinarily takes the form of a solid.

When a positive electrical pulse of just 0.8 volts is applied, it increases in volume by a factor of 120, absorbing surrounding water to become a gel – repeated pulses cause it expand further. Once a negative pulse of -0.8 volts is subsequently applied, however, it returns to being a solid. In this manner, it can be repeatedly switched back and forth between states.

A carbon fiber coated with the polymer, the latter seen here as a solid (top) and a gel (bottom)
A carbon fiber coated with the polymer, the latter seen here as a solid (top) and a gel (bottom)

In lab tests, it was found that the pores in a "smart sponge" filter made of the polymer changed in size by 85 percent as the material changed states, allowing for a number of possible applications.

"The properties of this smart filter can be dynamically changed to allow different types or different sizes of particle to pass through," says Linkoping's Prof. Magnus Berggren. "This function can be used for sieving, filtration, purification, and in process chemistry. It may also have applications in medicine and biochemistry."

And although other teams have previously developed materials that change state in response to an electrical signal, the best that could be managed was a doubling in volume.

A paper on the study, which was co-led by scientists Johannes Gladisch and Eleni Stavrinidou, recently appeared in the journal Advanced Science. The material can be seen in action, in the following video.

Reversible Electronic Solid Gel Switching of a Conjugated Polymer

Source: Linkoping University

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