The phenomenon of self-regulating polymer heaters has been unveiled.

Researchers at MIREA - Russian Technological University have unveiled the mechanisms behind self-regulating electroconductive polymer heaters made from specialized polymer composites containing carbon nanoparticles. They discovered that the ability of these heaters to significantly reduce their power output autonomously (without external control) is not solely attributed, as commonly believed, to the thermal expansion of the polymer when heated, but also to the onset of reversible degradation of the polymer's crystalline structure.

2024-12-19 10:00:12https://naked-science.ru/article/column/samoreguliruyushhihsya-po

A group of researchers from RTU MIREA has made a significant advancement in understanding the mechanisms behind self-regulating heaters made from crystallizing polyolefin compositions combined with electrically conductive carbon black containing nano-sized particles. It has been established that the self-regulating capability of these materials, manifested through an anomalously high positive thermal coefficient of electrical resistance, cannot be solely explained by the conventional thermal expansion of the material. The results are published in the journal "Thin Chemical Technologies".

Electrically conductive polymer composite materials with conductive carbon black are utilized in various fields. For instance, they are employed in coatings that conduct electricity, in screens that protect against static electricity, in devices that prevent electrical network overload, in sensors for measuring temperature and pressure, as well as in heaters that automatically regulate the temperature of pipelines during cold weather.

The scientists have demonstrated that in crystallizing polyolefin compositions, changes in the thermal coefficients of electrical resistance (transition from positive to negative coefficients) are linked to the onset of changes in the material's aggregate state. They proposed and justified a mechanism for the sharp increase in the electrical resistance of these compositions, which takes into account additional deformations of the material's crystalline phase caused by numerous expanding microvolumes of the melt that arise at the initial stages of melting with slight changes in the degree of crystallinity.

To conduct a comprehensive study of the structure and properties of crystallizing polyolefin compositions with conductive carbon black, various research methods were employed. Samples mimicking polymer heaters were created by pressing plates with embedded contact electrodes made from degreased brass mesh. The electrical characteristics of these samples were investigated in a specialized thermal chamber, while changes in the degree of crystallinity were assessed using differential scanning calorimetry. The dilatometric and rheological properties of the samples were studied using specialized equipment.

Anatoly Markov, a professor at the Department of Chemistry and Technology of Plastic and Polymer Composite Processing at RTU MIREA, emphasized that the research findings enhance the understanding of the processes occurring within materials during heating and open new possibilities for creating more efficient and reliable self-regulating heating devices that mimic natural processes.

The work was carried out in accordance with the initiative research program 195-ITXHT.