Multi-functional materials

Foto: Sam Rentmeester

Photo: Sam Rentmeester

Constructions need to be increasingly light and strong. That can be done, according to
Prof. Theo Dingemans (AE), almost exclusively using multi-functional materials.

 

A piece of carbon composite is lying on Dingemans’s desk, in the department of novel aerospace materials. ‘It is a wonderful material’, observes the professor. ‘As with so many materials in the aviation and aerospace industries, however, its density is somewhere between 1 and 1.5 grams.’

What Dingemans is trying to say is that the limits appear to have been reached. ‘We are now trying to push the boundaries by building additional functions into materials.’

According to Dingemans, one particularly promising area is the work that is being done on plastics that can act as both solar cells and coatings. Dr Johan Bijleveld is one of the researchers in Dingemans’s group who are working in this area. ‘We need a semi-conductive polymer, a polymer with many double bonds. One example would be polyazomethines.’ Bijleveld’s computer screen displays a graphic representation of a piece of polyazomethine. It is a concatenation of several rings of benzene and thiophene.

One unusual thing is the X that is built in somewhere in the middle of the molecule fragment. Bijleveld explains: ‘X is a side group that can do all sorts of things. Examples would be a nitrogen atom or an entire nitro or methoxy group. Some of these groups attract electrons, while others do not. By manipulating X, we can vary the electron density in the chain. This changes the efficiency with which the molecule transforms sunlight into electricity.’

‘The silicon solar panels that people currently have on their roofs achieve an efficiency level of 15%. We have not yet been able to surpass 2%.’

Numerous groups all around the world are working with this technology. ‘Some researchers are achieving yields in excess of 10%,’ notes Bijleveld, ‘but their polymers are expensive and very difficult to make. Our polymer, and thus our solar cell, can be ready within a week. It requires only three chemical steps at most.’

Thermo-electrical properties
Another promising material is the composite of plastic and carbon nano-tubes on which Bijleveld’s colleague, Dr Maruti Hegde, is working. The addition of carbon nano-tubes to the plastic makes the plastic behave in a semi-crystalline manner. It is extremely stiff, resistant to high temperatures and it has interesting thermo-electrical properties.

‘If you were coat an exhaust pipe with this material, you could use the temperature difference of several hundred degrees Celsius between one side of the exhaust pipe and the other to generate electricity’, Hegde explains.
‘Another feature that makes the material interesting is that it can be used to separate gasses. It could be used to filter carbon dioxide out of natural gas, for example. Believe me, you will be hearing a lot more about this
material.’

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