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Self-organizing, Self-healing Material of Magnetic Spinners

Jülich, 23 March 2020 – Smart and active materials can adapt their properties spontaneously in response to changing environmental conditions; these dynamically controllable properties have already led to a wide range of applications. Chromogenic materials, for example, enable window panes to darken automatically depending on the amount of light present, shock absorbers are able to adapt their dampening properties to prevailing road conditions with the help of magnetorheological fluids, and piezoelectric materials can be deformed by electric voltage, allowing robots to perform mechanical movements. An international team of scientists from Forschungszentrum Jülich and the US research institute Argonne National Laboratory has now developed a new, active system of magnetic microparticles. The material self-organizes in a non-equilibrium steady state in the presence of a rotating magnetic field, and possesses potentially useful properties such as self-healing and controllable transport capabilities.

The researchers studied magnetic nickel microparticles moving at an air-water interface. They set the particles, which are less than a tenth of a millimetre in size, into circular motion using a magnetic field rotating in the plane of the water’s surface. They investigated their reaction as a function of various parameters, such as rotational frequency and particle concentration.

“The system exhibits properties which – unlike systems studied to date – are based solely on the rotation of the particles and can be controlled externally with the help of the magnetic field. This makes it interesting for both basic research and applications”, reports Prof. Gerhard Gompper, Director at the Institute for Biological Information Processes and the Institute for Advanced Simulation, who, together with colleagues in Jülich, complemented the experimental studies in the USA with theoretical simulations. This enabled the researchers to explain various observations and to gain insight into microscopic mechanisms.

Depending on the frequency of the magnetic field, the nickel particles cluster together to form shorter or longer rotating chains. Furthermore, the chains arrange themselves spontaneously and dynamically at the interface of water and air in a crystal-like structure and restore this order even after a disturbance has occurred. The researchers tested this by dropping a larger particle into their arrangement. The self-healing process takes only a few seconds.

In contrast to previous experimental designs in which the magnetic field oscillates, the experimental setup used by the researchers allowed the particles to rotate synchronously, leading to a repulsion effect between the chains caused by the rotation of the liquid, thereby making the crystal-like arrangement possible in the first place.

In further tests, gold particles, which are not magnetic and not influenced by the magnetic field, were added to the experiments and simulation. The researchers were in this way able to observe that such particles can be actively transported through the system and that this transport can be controlled externally. Discrepancies between the experimental and theoretical transport properties indicate a complex interplay between the rotating aggregates and the liquid, which needs to be studied further.

Image and video material:

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In the video of the experiment, the rotating chains are displayed as dark rods. The different views show how the chains set the surrounding water in motion (left), the resulting water vortices (middle) and the associated flow lines (right).

Source: Argonne National Laboratory. Video published in Han et al., Sci. Adv. 2020; 6 : eaaz8535 under Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC)

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The simulation shows how the rotating chains (red) actively transport a non-magnetic particle (blue).

Source: Forschungszentrum Jülich. Video published in Han et al., Sci. Adv. 2020; 6 : eaaz8535 under Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC)

Original publication::

Reconfigurable structure and tunable transport in synchronized active spinner materials;
K. Han, G. Kokot, S. Das, R. G. Winkler, G. Gompper, A. Snezhko;
Science Advances 20 Mar 2020: Vol. 6, no. 12, eaaz8535, DOI: 10.1126/sciadv.aaz8535

Further information:

Website of the Institute for Biological Information Processes – Theoretical Physics of Living Matter /Institute for Advanced Simulation –Theory of Soft Matter and Biophysics (IBI-5/IAS-2)

Website of the Materials Science Division of the Argonne National Laboratory

Contact:

Prof. Dr. Gerhard Gompper
Forschungszentrum Jülich
Theoretical Physics of Living Matter /Theoretical Soft Matter and Biophysics (IBI-5/IAS-2)
Tel: +49 2461 61-4012
Email: g.gompper@fz-juelich.de

Press contact:

Angela Wenzik, Science Journalist
Forschungszentrum Jülich
Tel: +49 2461 61-6048
Email: a.wenzik@fz-juelich.de


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