Characterisation of the magnetic response of nanoscale magnetic filaments in applied fields

Incorporating magnetic nanoparticles (MNPs) within permanently crosslinked polymer-like structures opens up the possibility for synthesis of complex, highly magneto-responsive systems. Among such structures are chains of prealigned magnetic (ferro- or super-paramagnetic) monomers, permanently crosslinked by means of macromolecules, which we refer to as magnetic filaments (MFs). In this paper, using molecular dynamics simulations, we encompass filament synthesis scenarios, with a compact set of easily tuneable computational models, where we consider two distinct crosslinking approaches, for both ferromagnetic and super-paramagnetic monomers. We characterise the equilibrium structure, correlations and magnetic properties of MFs in static magnetic fields. Calculations show that MFs with ferromagnetic MNPs in crosslinking scenarios where the dipole moment orientations are decoupled from the filament backbone, have similar properties to MFs with super-paramagnetic monomers. At the same time, magnetic properties of MFs with ferromagnetic MNPs are more dependent on the crosslinking approach than they are for ones with super-paramagnetic monomers. Our results show that, in a strong applied field, MFs with super-paramagnetic MNPs have similar magnetic properties to ferromagnetic ones, while exhibiting higher susceptibility in low fields. We find that MFs with super-paramagnetic MNPs have a tendency to bend the backbone locally rather than to fully stretch along the field. We explain this behaviour by supplementing Flory theory with an explicit dipole-dipole interaction potential, with which we can take in to account folded filament configurations. It turns out that the entropy gain obtained through bending compensates an insignificant loss in dipolar energy for the filament lengths considered in the manuscript. © 2020 The Royal Society of Chemistry.Austrian Science Fund, FWF: START-Projekt Y 627-N27Russian Science Foundation, RSF: 19-12-00209This 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)

The influence of crosslinkers and magnetic particle distribution along the filament backbone on the magnetic properties of supracolloidal linear polymer-like chains

Diverse polymer crosslinking techniques allow the synthesis of linear polymer-like structures whose monomers are colloidal particles. In the case where all or part of these colloidal particles are magnetic, one can control the behaviour of these supracolloidal polymers, known as magnetic filaments (MFs), by applied magnetic fields. However, the response of MFs strongly depends on the crosslinking procedure. In the present study, we employ Langevin dynamics simulations to investigate the influence of the type of crosslinking and the distribution of magnetic particles within MFs on their response to an external magnetic field. We found that if the rotation of the dipole moment of particles is not coupled to the backbone of the filament, the impact of the magnetic content is strongly decreased. © 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

The Impact of Magnetic Field on the Conformations of Supracolloidal Polymer-like Structures with Super-paramagnetic Monomers

We investigate the properties of magnetic supracolliodal polymers – magnetic filaments (MFs) – with super-paramagnetic monomers, with and without Van der Waals (VdW) attraction between them. We employ molecular dynamics (MD) simulations to elucidate the impact of crosslinking mechanism on the structural and magnetic response of MFs to an applied external homogeneous magnetic field. We consider two models: plain crosslinking, which results in a flexible backbone; and constrained crosslinking, which provides significant stiffens against bending. We find that for plain crosslinking, even a slight increase of the central attraction leads to collapsed MF conformations. Structures that initially exhibit spherical symmetry evolve into cylindrically symmetric ones, with growing magnetic field strength. Plain crosslinking also allows for conformational bistability. MFs with constrained crosslinking tend to, instead, unravel in field. In both crosslinking scenarios, central attraction is able to hinder low-field magnetic response of MFs, albeit the bistability of plainly crosslinked MFs manifests itself also in the high-field region. © 2020 Elsevier B.V.This research has been supported by the Russian Science Foundation Grant No. 19-72-10033 . S.S.K acknowledges support from the Austrian Science Fund (FWF), START-Projekt Y 627-N27

Divalent Multilinking Bonds Control Growth and Morphology of Nanopolymers

Assembly of nanoscale objects into linear architectures resembling molecular polymers is a basic organization resulting from divalent interactions. Such linear architectures occur for particles with two binding patches on opposite sides, known as Janus particles. However, unlike molecular systems where valence bonds can be envisioned as pointlike interactions nanoscale patches are often realized through multiple molecular linkages. The relationship between the characteristics of these linkages, the resulting interpatch connectivity, and assembly morphology is not well-explored. Here, we investigate assembly behavior of model divalent nanomonomers, DNA nanocuboid with tailorable multilinking bonds. Our study reveals that the characteristics of individual molecular linkages and their collective properties have a profound effect on nanomonomer reactivity and resulting morphologies. Beyond linear nanopolymers, a common signature of divalent nanomonomers, we observe an effective valence increase as linkages lengthened, leading to the nanopolymer bundling. The experimental findings are rationalized by molecular dynamics simulations. © 2021 The Authors. Published by American Chemical Society.This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, grant DE-SC0008772. This research used resources of the Center for Functional Nanomaterials and National Synchrotron Light Source II, supported by U.S. DOE Office of Science Facilities at Brookhaven National Laboratory under Contract No. DE-SC0012704. This research used imaging facilities of Advanced Science Research Center at City University of New York. D.M., P.A.S., and S.K. acknowledge support from the Austrian Research Fund (FWF), Project P33748. S.K. was also supported by the Russian Science Foundation Grant 19-12-00209 for computational work. Computer simulations were performed at the Vienna Scientific Cluster (VSC4)

Erratum: Characterisation of the magnetic response of nanoscale magnetic filaments in applied fields (Nanoscale (2020) (DOI: 10.1039/d0nr01646b)

The authors regret that the affiliations were incorrectly shown in the original manuscript. Affiliations a and c have been amended, and affiliation d has been added. The correct list of affiliations is as shown above. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers. © 2020 The Royal Society of Chemistry