Polymer nanocarpets to electrify smart fabrics

Researchers from Tomsk Polytechnic University together with their international colleagues have discovered a method to modify the ultra-thin conductor of current and heat graphene without destroying it. Thanks to the novel method the researchers were able to synthesize on graphene samples of a well-structured polymer with a strong covalent bond, which they called ‘polymer carpets’. The entire structure is highly stable; it is less prone to degradation over the time that makes the study promising for the development of organic flexible electronics. In addition, if a layer of molybdenum disulphide is added over the ‘nanocarpet’, the resulting structure generates current under exposure to light. The study results were published in Journal of Materials Chemistry C (IF: 5.256; Q1).

Photo: The scheme for obtaining a hybrid structure of "graphene-polymer".

Graphene is simultaneously the most durable, light and an electrically conductive carbon compound. It can be used for manufacturing solar batteries, smartphone screens, thin and flexible electronics, and even in water filters since graphene films pass water molecules and stop all other compounds. Graphene should be integrated into complex structures to be used successfully. However, it is a challenge. According to scientists, graphene itself is stable enough and reacts poorly with other compounds. In order to react it with other elements, i.e. to modify it, graphene is destroyed. This affects the properties of the materials obtained.

Professor Raul Rodrigez from the Research School for Chemistry & Applied Biomedical Sciences says: ‘When destroying graphene, you should be very careful. If you overdo, the unique properties of graphene are lost. Therefore, we decided to follow a different path.

In graphene, there are inevitable nanodefects, for example, at the junction of faces. Hydrogen atoms are often attached to such defects. It is this hydrogen that can interact with other elements.’

To modify graphene, the authors use a thin metal substrate on which a graphene layer is placed. Then graphene is covered with the solution of bromine-polystyrene molecules. The molecules interact with hydrogen and are attached to the existing defects, resulting in polyhexylthiophene (P3HT). Further exposed to light during the photocatalysis, a polymer begins to ‘grow’.

‘In the output we obtained the samples which structure resembles ‘polymer carpets’ as we name then in the paper. Above such a ‘polymer carpet’ we place molybdenum disulphide.

Due to a unique combination of materials, we obtain ‘sandwich’ structure’ that functions like a solar battery. That is, it generates current exposed to light.

In our experiments a strong covalent bond is established between the molecules of the polymer and graphene, that is critical for the stability of the material obtained,’ notes Rodrigez.

According to the researcher, the method for graphene modification, on the one hand, enables to obtain a very strong compound, on the other hand, it is rather simple and cheap as affordable compounds are used. The method is versatile because it makes it possible to react graphene with very different polymers.

‘The strength of the obtained compound is achieved additionally because of that we do not destroy graphene itself and use existing defects, and a strong covalent bond between polymer molecules. This allows us to consider the study as promising for the development of thin and flexible electronics, when solar batteries can be attached to clothes, and when deformed they will not break down,’ the professor explains.