Nickel nanoparticles have been intensively studied over the years proving their worth in biomedical, electronic, physical, and chemical applications. One of the exclusive features of the ferromagnetic nanoparticles is a field-directed assembly. Specifically, magnetic fields can be utilized to generate strong dipole-dipole interactions causing the particles to assemble in quite rigid chains. The rigidity is a direct consequence of strong magnetic interaction between the particles.  In this communication, we describe fabrication of flexible chains of ferromagnetic Ni nanoparticles that possess ability to adapt other than the rigid (nearly) straight configurations in the absence of external magnetic field.  The chains obtained orient in a magnetic field forming magnetic rods. However, they collapse into globule upon removal of the magnetic field. The re-application of the magnetic field causes the collapsed chain to unfold restoring rod orientation along the field.  The flexibility of the ferromagnetic particle chains in the system originates from layer of the grafted polyethylene glycol (PEG) macromolecules enveloping the each nanoparticle in the chain.  The densely grafted macromolecules form a polymer brush on the Ni particles, where the constrained geometrical environment limits the available space the polymers can occupy forcing the chains to stretch our normal to the surface.  The polymer brush provides steric repulsive barrier around the nanoparticles preventing their aggregation, regulates distance between nanoparticles in the ferromagnetic chains, and allows for the rotation of particles in the chains.

Flexible ferromagnetic chains from polymer grafted nickel nanoparticles

248th National Meeting (2014)

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