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Moscow scientists propose measuring nanoobjects using ultrasound

April 20, 18:10 UTC+3 MOSCOW

During the research, the scientists passed an ultrasonic wave through a solution of nanotubes which served to define their length and thickness

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© MIPT press service

MOSCOW, April 20. /TASS/ A research team from the Moscow Institute of Physics and Technology (MIPT) has developed a technique for measuring the length and diameter of nanotubes and nanofibres suspended in water, MIPT’s press office said.

During the research, the scientists passed an ultrasonic wave through a solution of nanotubes which served to define their length and thickness. This method could be potentially applied to measuring any nanoobjects, as noted in the announcement.

"The established technique can be used to define diameter and length of lengthy nanoobjects of an arbitrary composition. In this work, we have chosen carbon nanomaterials as objects because of their high applicability," Viktor Ivanov, chief of the research, corresponding member of RAS and head of Department of Electronics, Photonics, and Molecular Physics at MIPT commented.

Carbon nanotubes and nanofibres represent an especially stable and flexible nanomaterial with high electric and thermal conductivity. The application range of nanotubes is constantly expanded. For instance, they are used for creating new materials in form of colloid solutions. Among other numerous cases, the nanotubes can be added to the anode of a lithium-ion battery to increase its power capacity, whereas by adding a few nanotubes to a polymer, one can turn the polymer to a conductive material.

In order to prepare a colloid solution with equally distributed particles which do not coagulate, it is crucial to know their precise size. This information will allow for controlling the composition of the solution. The researchers decided to use ultrasound to measure the diameter of nanotubes. While the ultrasound was passing through the solution, the size of suspended particles could be defined by tracking the attenuation of the sound, as the size of particles directly influences the wave attenuation coefficient. In the recent studies, the ultrasound has been already applied to measure the diameter of spherical nanoparticles but this method has not been used so far for defining the length of nanotubes.

Measurement technique

The researchers decided to conduct its measurement using the customary method, the diameter of nanotubes in the model solution where all the tubes are oriented parallel to each other, and then to study the attenuation in the solution of equal concentration but with tubes oriented chaotically. By comparing the results of measurements for chaotic and assembled solutions, one can calculate the length of nanotubes if the diameter and the diameter/length ratio are known.

In the laboratory of MIPT, an experiment was conducted where the colloid solution was moving through a tight rubber tube with an acceleration in such a way that the nanotubes in the solution were oriented in one direction. The researchers carried out measurements in the rubber tube, compared the results to those of a randomized solution, and deduced the length of nanotubes followed by the successful validation of a computed parameter with a microscope. The scientists presume this method is applicable to size measurements of any other nanoobjects.

"We developed a method of measuring sizes of cylindrical nanoobjects, in which the length is greater than the diameter. However, we believe, that a similar technique might be applied to the opposite case to study nanoobjects having a diameter greater than the length, i.e. for nanodiscs including for instance graphene," Ivanov said.

The results of the research presented in the article have been published recently in the journal Colloids and Surfaces A: Physicochemical and Engineering Aspects.

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