23.09.2016 change 23.09.2016

Invisible tanks and magnetic drugs, or nanotubes in action

They can make a tank invisible to radar; they can carry a drug and poison cancer cells; they can also extend the life of automobile engines. Carbon nanotubes are gaining more and more applications. Some of them are being tested by a team from Silesian University of Technology.

Chemists from the Silesian University of Technology team led by Dr. Sławomir Boncel have been searching for several years for new applications for carbon nanotubes already produced on a mass scale, and studying their properties. The latest idea of Silesian scientists are "invisible nanotubes", which can be used in military camouflage. The project is carried out together with the Institute of Security Technology "Moratex" in Łódź, Military Institute of Armament Technology in Zielonka near Warszawy and Miranda Sp. z o.o.

How does a naturally black material, which is carbon, become invisible? It\'s not about invisibility to the human eye, but to the "eye" of a radar. According to the laws of physics, radar signal falling on the object should be reflected, passed, dispersed or absorbed and then converted into heat. Covering an object with a structure of nanotube, however, means that the signal sent in its direction does not come back - it is absorbed or dispersed. Produced heat - thanks to the high thermal conductivity of nanotubes - is also dissipated. As a result, the object becomes "invisible" to radars, night vision and thermal imaging cameras.

"Properties of materials change drastically when you reduce their size, going to the nanoscale" - said Dr. Sławomir Boncel. "Sometimes such tests lead to a change of some well-known truths about the materials. Steel that we have used for a long time has certain properties, such as a specific melting point. But it becomes a completely different steel if we move its structure the nano-scale. Then, its melting point is radically different, as are other properties, magnetic for example" - explained the researcher.

Dr. Boncel\'s team does not focus on one application of carbon nanotubes. In another project, scientists want to use the nanomaterial as a drug carrier.

"We are introducing a magnetic particle into the nanotube core, apply the drug on the surface, and introduce the entire +hybrid+ into the bloodstream" - explained the researcher. "By applying a local magnetic field near the tumour, we bring the nanotube carrying the drug to the right place, in which it should act. In addition, we protect the surrounding healthy tissue, because such treatment targets only the affected place. Interestingly, the nanotubes do not exhibit toxicity for the cells of our immune system, so-called macrophages, which are the +first line of defence+, but are toxic for tumour cells. Thus, we have a highly selective, limited to cancer only, double therapeutic effect - of the drug and the nanotube itself. Such studies are, however, very complex, because each cell type is different and our nanostructures can have different effects" - emphasised the researcher.

On the other hand, together with the company Winiplast from Orzesze, with the funding from the Foundation for Polish Science, the Silesian scientists have developed liquids containing carbon nanotubes with increased thermal conductivity.

"The nanotubes have excellent thermal conductivity" - said Dr. Boncel. Members of his team decided to find out how the thermal conductivity of liquids such as water and commonly used glycols would increase if they were enriched with carbon nanotubes. It turned out that in combination with carbon nanotubes, the thermal conductivity of such liquid increases by 30 percent, and a heat transfer coefficient of the turbulent flow of such "nanoliquid" - by 100 percent.

What could liquids enriched with carbon nanotubes be used for? "If we have a Ferrari engine that has a certain life and we can cool down it with properly +spiced+ liquids by, say, about 2 degrees Celsius, we will extend its life by a few dozen months. This means huge savings" - explained the researcher.

Although scientists from his team spend most of their time on application research, they conduct basic research on the functionalisation of nanotubes, i.e. chemical modifications that alter their basic properties. For example, carbon nanotubes (originally insoluble) may be modified to dissolve in water, oil or another type of solvent. Thanks to these modifications, in the future it could be possible to adapt nanotubes for the needs of other industries, for example for textiles - so that they can be integrated into fabrics.

And what about the emission of nanotubes into the environment? After all, anything that gets there - does not disappear, nor is it neutral. Dr. Boncel noted that environmental hazard from carbon nanomaterials is a relatively new subject. The potential threat from nanomaterials has been discussed only for a few-dozen years. At the same time, the number of studies in this field is growing.

According to the researcher, comparing nanotubes to asbestos is not justified. "Nanotubes - unlike with asbestos, repeatedly compared to them - are +digestible+ by enzymes called peroxidases. Of course there is a risk of dangerous cellular response after nanotubes enter the respiratory system, but it is associated also with a number of finely divided solids such as sand or flour. An important factor is, therefore, the type, time and degree of exposure "- he explained.

Dr. Boncel noted that we also need to distinguish between the toxicity of nanomaterials in relation to human cells and in relation to other groups of organisms, or their ecotoxicology. "People may be exposed to nanomaterials mainly by inhalation, and that can be dangerous. Skin contact or ingestion is very limited. In contrast, other organisms, plants, animals or micro-organisms may have much more contact. This means that nanostructures may affect them more strongly" - he explains.

Generally speaking, the toxicity of carbon nanotubes depends on the geometry - structure, the degree of agglomeration (compaction), and functionalisation (chemical modification). "However, the presence and effects of these structures in the environment are fairly complex problem, and studies in this field are only in the initial phase" - added Dr. Boncel.

PAP - Science and Scholarship in Poland, Aleksandra Ziembińska-Buczyńska

The text is one of the results of the program Proponents of Science, organized by the Copernicus Science Centre and the British Council Foundation. The program facilitates establishing cooperation between scientists who popularise knowledge and science journalists.

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