To be able to work with these incredibly small nano-particles demands ingenious methods to manage and organise them. One method is to employ so-called self-assembly – to design the particles in such a way that they can be governed to organise themselves into predetermined structures.
Certain material phenomena change at the nano-level, such as conductivity and magnetic properties. The challenge lies in being able to control this in detail, both in the generation of different nano-particles and when they are assembled into new material, explains Lennart Bergström, professor of material chemistry.

 
Lennart Bergström
 

His research group at the Department of Material and Environmental Chemistry has, among other things, created iron-oxide particles in the form of identical small nano-cubes. As these are also magnetic, how they organise themselves into larger structures can be governed with the help of relatively weak electromagnetic fields, for example those generated by simple toy magnets. Using a unique model system they have developed it is now possible to test different ways of assembling iron-oxide particles and studying how this affects their properties.
"We are attempting, exactly as mathematicians did 2000 years ago, to discover the best different ways to pack three-dimensional geometric bodies. Possible applications for this type of material include data storage and medical devices," says Lennart Bergström.

In many cases inspiration comes from nature, which is skilled at building complex structures using simple methods. Different ways of arranging nano-particles into thin layers has found inspiration, for example, in the wings of butterflies, where different wing structures reflect light of different colours.
"Another organism we are inspired by is the snail, the shell of which is very hard but nonetheless does not crack easily. This is because it is built up of layers of hard calcium crystals and softer proteins," Lennart Bergström explains.

Lennart Bergström employs the method of utilising the best characteristics of different components to create new material, based on common raw materials found in forests. Using enzymes and acids it is possible to break down wood fibres into their minutest constituent parts, which are cylindrical nano-cellulose crystals. These can then be reassembled with substances to form different composite materials.
"Researchers at KTH have shown how it is possible to make transparent paper, for example, where the small cellulose fibres are too small to reflect light. Our interest is to go further and generate new nano-paper based on composites that have different magnetic and optical properties, for example. My colleague German Salazar-Alvarez has already generated magnetic nano-paper using iron-oxide particles," Lennart Bergström informs.

Research on nano-materials is relatively new at the department. Lennart Bergström's research group comprises around 15 people and many have come from around the world.
"Chemistry research at Stockholm University ranks in the top 50 in the world and we see that many people want to come here. It is a privilege to work with ambitious young people who are driven by a thirst for new knowledge, regardless of where they come from, and this is one of the most fun aspects of my job," Lennart Bergström concludes.

The research forms part of the Material Chemistry area, one of 30 pre-eminent areas at Stockholm University. The detailed study of different substances is combined with the development of new nano-materials, ceramics and porous material that can be used in areas such as healthcare, energy and environmental technology. One of our strengths is world-leading research where material is investigated down to the single atom level using electron microscopy.
 

Text: Andreas Nilsson

Translation: AAR Translator