The influence of an applied magnetic field on the self-assembly of magnetic nanogels

Using Langevin dynamics simulations, we investigate the self-assembly of magnetic nanogels in the presence of applied magnetic fields of moderate strength. We find that even weak fields lead to drastic changes in the structure factors of both, the embedded magnetic nanoparticles and of whole nanogel particles. Nanogels assemble by uniting magnetic particle clusters forming inter-gel bridges. At zero field the average amount of such bridges for a pair of nanogels is close to one, whereas even for weak fields it fastly doubles. Rapid growth of cluster size at low values of the applied field is followed by a broad region of slow increase, caused by the mechanical constraints imposed the polymer matrix. The influence of the latter manifests itself in both, the slow growth of the magnetisation curve at intermediate fields and the slow decay of the total Zeeman energy. © 2020This research has been supported by the Russian Science Foundation Grant 19-72-00209 . Authors are grateful to A. O. Ivanov for valuable discussions concerning structure factors and to E. S. Pyanzina for providing the code for calculation of chain partition functions in an applied magnetic field. The work was also supported by the FWF START-Projekt Y 627-N27 . Simulations were performed in the Vienna Scientific Cluster (VSC3)

Suspensions of magnetic nanogels at zero field: Equilibrium structural properties

Magnetic nanogels represent a cutting edge of magnetic soft matter research due to their numerous potential applications. Here, using Langevin dynamics simulations, we analyse the influence of magnetic nanogel concentration and embedded magnetic particle interactions on the self-assembly of magnetic nanogels at zero field. For this, we calculated radial distribution functions and structure factors for nanogels and magnetic particles within them. We found that, in comparison to suspensions of free magnetic nanoparticles, where the self-assembly is already observed if the interparticle interaction strength exceeds the thermal fluctuations by approximately a factor of three, self-assembly of magnetic nanogels only takes place by increasing such ratio above six. This magnetic nanogel self-assembly is realised by means of favourable close contacts between magnetic nanoparticles from different nanogels. It turns out that for high values of interparticle interactions, corresponding to the formation of internal rings in isolated nanogels, in their suspensions larger magnetic particle clusters with lower elastic penalty can be formed by involving different nanogels. Finally, we show that when the self-assembly of these nanogels takes place, it has a drastic effect on the structural properties even if the volume fraction of magnetic nanoparticles is low. © 2019 Elsevier B.V.This research has been supported by the Russian Science Foundation Grant No. 19-12-00209 . Authors acknowledge support from the Austrian Research Fund (FWF), START-Projekt Y 627-N27. Computer simulations were performed at the Vienna Scientific Cluster (VSC-3)

Stockmayer supracolloidal magnetic polymers under the influence of an applied magnetic field and a shear flow

The idea of creating magnetically controllable colloids whose rheological properties can be finely tuned on the nano- or micro-scale has caused a lot of experimental and theoretical effort. The latter resulted in systems whose building blocks are ranging between single magnetic nanoparticles to complexes of such nanoparticles bound together by various mechanisms. The binding can be either chemical or physical, reversible or not. One way to create a system that is physically bound is to let the precrosslinked supracolloidal magnetic polymers (SMPs) to cluster due to both magnetic and Van-der-Waals-type forces. The topology of the SMPs in this case can be used to tune both magnetic and rheological properties of the resulting clusters as we show in this work. We employ Molecular Dynamics computer simulations coupled with explicit solvent modelled by Lattice-Boltzmann method in order to model the behaviour of the clusters formed by chains, rings, X- and Y-shaped SMPs in a shear flow with externally applied magnetic field. We find that the shear stabilises the shape of the clusters not letting them extend in the direction of the field and disintegrate. The clusters that show the highest response to an applied field and higher shape stability are those made of Y- and X-like SMPs. © 2023 Elsevier B.V.Russian Science Foundation, RSF: 19-72-10033, SAM P 33748The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Ekaterina Novak reports financial support was provided by Russian Science Foundation. Sofia Kantorovich reports financial support was provided by Austrian Science Fund.This research has been supported by the RSF Grant No.19-72-10033. S.S.K. was partially supported by Project SAM P 33748. Computer simulations were performed at the Vienna Scientific Cluster (VSC) and at the Ural Federal University Cluster.This research has been supported by the RSF Grant No. 19-72-10033 . S.S.K. was partially supported by Project SAM P 33748 . Computer simulations were performed at the Vienna Scientific Cluster (VSC) and at the Ural Federal University Cluster

СОПОСТАВЛЕНИЕ КОСМИЧЕСКИХ ИЗОБРАЖЕНИЙ ПОВЕРХНОСТИ ЗЕМЛИ С ЭТАЛОНОМ ЦИФРОВОЙ КАРТЫ МЕСТНОСТИ

In article problems of comparison of space pictures with a standard of a digital district map for tasks of updating of cartographical information and monitoring of the territories are considered. The purpose is development of a technique of automated detection of cumulative changes in space pictures concerning a standard of a digital district map in optionally the set analysis window. Researches and development of a technique were made by mathematical simulation of the task in the environment of MATLAB. The last results of researches in the form of the developed technique of detection of cumulative changes of object composition in the orthotransformed and geobound space pictures of the Earth’s surface concerning a standard of a vectorial digital district map are given in article. The main results of comparison of space pictures to a digital district map received in case of tests of the developed technique are shown. Application of this technique allows to automate process already now and to reduce time of the subject analysis of the space information obtained by Earth remote-sensing instruments for topographical mapping.В статье рассматриваются проблемы сопоставления космических снимков с эталоном цифровой карты местности для задач актуализации картографической информации и мониторинга территорий. Целью является разработка методики автоматизированного выявления совокупных изменений на космических снимках относительно эталона цифровой карты местности в опционально задаваемом окне анализа. Исследования и разработка методики производились путём математического моделирования задачи в среде MATLAB. В статье приводятся последние результаты исследований в виде разработанной методики выявления совокупных изменений объектного состава на ортотрансформированных и геопривязанных космических снимках поверхности Земли относительно эталона векторной цифровой карты местности. Показаны основные результаты сопоставления космических снимков с цифровой картой местности, полученные при испытаниях разрабатываемой методики. Применение данной методики уже сейчас позволяет автоматизировать процесс и сократить время тематического анализа космической информации, получаемой средствами дистанционного зондирования Земли для топографического картографирования

Behaviour of a Magnetic Nanogel in a Shear Flow

Magnetic nanogels (MNG) – soft colloids made of polymer matrix with embedded in it magnetic nanoparticles (MNPs) – are promising magneto-controllable drug carriers. In order to develop this potential, one needs to clearly understand the relationship between nanogel magnetic properties and its behaviour in a hydrodynamic flow. Considering the size of the MNG and typical time and velocity scales involved in their nanofluidics, experimental characterisation of the system is challenging. In this work, we perform molecular dynamics (MD) simulations combined with the Lattice-Boltzmann (LB) scheme aiming at describing the impact of the shear rate (γ̇) on the shape, magnetic structure and motion of an MNG. We find that in a shear flow the centre of mass of an MNG tends to be in the centre of a channel and to move preserving the distance to both walls. The MNG monomers along with translation are involved in two more types of motion, they rotate around the centre of mass and oscillate with respect to the latter. It results in synchronised tumbling and wobbling of the whole MNG accompanied by its volume oscillates. The fact the an MNG is a highly compressible and permeable for the carrier liquid object makes its behaviour different from that predicted by classical Taylor-type models. We show that the frequency of volume oscillations and rotations are identical and are growing function of the shear rate. We find that the stronger magnetic interactions in the MNG are, the higher is the frequency of this complex oscillatory motion, and the lower is its amplitude. Finally, we show that the oscillations of the volume lead to the periodic changes in MNG magnetic energy. © 2021 Elsevier B.V.This research has been supported by the Russian Science Foundation Grant No.19-12-00209. Computer simulations were performed at the Vienna Scientific Cluster (VSC). I.S.N. and S.S.K. are grateful to Vienna Doctoral School Physics, Doctoral College DCAMF and were partially supported by FWF Project SAM P 33748. The authors thank Pedro S. Sánchez and Dr. Rudolf Weeber for fruitful discussions and useful recommendations

ORB5: a global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry

This paper presents the current state of the global gyrokinetic code ORB5 as an update of the previous reference [Jolliet et al., Comp. Phys. Commun. 177 409 (2007)]. The ORB5 code solves the electromagnetic Vlasov-Maxwell system of equations using a PIC scheme and also includes collisions and strong flows. The code assumes multiple gyrokinetic ion species at all wavelengths for the polarization density and drift-kinetic electrons. Variants of the physical model can be selected for electrons such as assuming an adiabatic response or a ``hybrid'' model in which passing electrons are assumed adiabatic and trapped electrons are drift-kinetic. A Fourier filter as well as various control variates and noise reduction techniques enable simulations with good signal-to-noise ratios at a limited numerical cost. They are completed with different momentum and zonal flow-conserving heat sources allowing for temperature-gradient and flux-driven simulations. The code, which runs on both CPUs and GPUs, is well benchmarked against other similar codes and analytical predictions, and shows good scalability up to thousands of nodes