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Download fileField-Driven Reversible Alignment and Gelation of Magneto-Responsive Soft Anisotropic Microbeads
journal contribution
posted on 2021-07-13, 06:29 authored by Natasha
I. Castellanos, Bhuvnesh Bharti, Orlin D. VelevMagnetic
fields offer untethered control over the assembly, dynamics,
and reconfiguration of colloidal particles. However, synthesizing
“soft” colloidal particles with switchable magnetic
dipole moment remains a challenge, primarily due to strong coupling
of the dipoles of the adjacent nanoparticles. In this article, we
present a way to overcome this fundamental challenge based on a strategy
to synthesize soft microbeads with tunable residual dipole moment.
The microbeads are composed of a polydimethylsiloxane (PDMS) matrix
with internally embedded magnetic nanoparticles (MNPs). The distribution
and orientation of the MNPs within the PDMS bead matrix is controlled
by an external magnetic field during the synthesis process, thus allowing
for the preparation of anisotropic PDMS microbeads with internal magnetically
aligned nanoparticle chains. We study and present the differences
in magnetic interactions between microbeads containing magnetically
aligned MNPs and microbeads with randomly distributed MNPs. The interparticle
interactions in a suspension of microbeads with embedded aligned MNP
chains result in the spontaneous formation of percolated networks
due to residual magnetization. We proved the tunability of the structure
by applying magnetization, demagnetization, and remagnetization cycles
that evoke formation, breakup, and reformation of 2D percolated networks.
The mechanical response of the microbead suspension was quantified
by oscillatory rheology and correlated to the propensity for network
formation by the magnetic microbeads. We also experimentally correlated
the 2D alignment of the microbeads to the direction of earth’s
magnetic field. Overall, the results prove that the soft magnetic
microbeads enable a rich variety of structures and can serve as an
experimental toolbox for modeling interactions in dipolar systems
leading to various percolated networks, novel magneto-rheological
materials, and smart gels.