Modern capacitors – devices that accumulate charge and electric field energy – require the development of flexible dielectrics, i.e., materials with poor conductivity. These include polypropylene, a flexible and durable polymer. However, polymers cannot accumulate external field energy very well, which hinders their use as transistors and electric drives. This problem could be solved with the help of two-dimensional particles, MXenes, the addition of which leads to the formation of microcapacitors inside the polymer: nanoparticles act as electrodes (elements that conduct current), with the polymer itself as a dielectric. As a result of exposure to an external electric field, polarisation centres (charge displacement zones) arise at the boundaries of contact between MXenes and the polymer, causing the composite to accumulate charge more effectively.
MXenes typically consist of a transition metal, such as titanium, vanadium or chromium, and a carbon or nitrogen atom. The scientists from the Yuri Gagarin State Technical University of Saratov and Southern Federal University conducted a study on how the nanoparticles of vanadium carbide, a MXene compound of vanadium and carbon, can affect the charge-accumulating ability of polyvinylidene fluoride (PVDF). PVDF is a fluorinated polymer that combines rigidity and low flammability.
The synthesis of vanadium nanoparticles took place in two stages. First, the scientists carried out high-temperature synthesis of vanadium, aluminum powder and graphite, which produced a precursor material. The material was placed in a hot solution of hydrochloric and hydrofluoric acids, which ultimately made it possible to obtain MXenes from vanadium and carbon without aluminum impurities.
The authors of the study ground the resulting powder and mixed it with an organic solvent. The scientists dissolved PVDF granules in the mixture, pressing 1-millimeter-thick polymer discs at a temperature of 180 degrees Celsius. In order to determine the molecular structure of the resulting polymer, the scientists used the X-ray crystallography method, which makes it possible to evaluate the structure of a substance based on the scattering of X-rays. As for the substance’s charge-accumulating ability, the scientists used an impedance meter, a device that tracks the movement of charges.
Calculations showed that the ability of the polymer to accumulate external field energy had increased by 41.7 times. This sharp increase was made possible by the fact that, thanks to two-dimensional vanadium carbide, the polymer adopted a new crystalline structure. This discovery could facilitate the use of polymers in various branches of electronics.
“The polymer composites we have obtained could become part of various electronic circuits. For instance, capacitors based on these composites might find their application in automaking and aircraft engineering. In the future, we plan to focus on materials for high-voltage cable joints, since such compounds effectively equalise high-tension fields,” Nikolai Gorshkov, one of the authors of the study and candidate of technical sciences, is quoted as saying by the Russian Science Foundation.
