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Mechanical properties of superparamagentic nanorods

MSC : Loudjy Chevry, Minhao Yan, Jean-François Berret, Fabien Gerbal

The dialysis of dispersions containing oppositely charged iron oxide particles and polymers under a constant magnetic field induces the growth of anisotropic aggregates. This experimental protocol allows the fabrication of superparamagnetic nanorods of lengths 1 - 100 μm and of diameter of 200 nm. The mechanical behavior of the magnetic rods is Hookean : under small deformations, their bending response is elastic. Using optical microscopy, we design an experiment to measure the bending modulus of a single rod using two approaches. The first experiment consists in evaluating the thermal fluctuations of the rods at room temperature as a function of the length. The second experiment consists in the determination of the bending laws under the application of a constant magnetic field. From these two experiments, the persistence length of the rod as well as the Young modulus of the nanostructured material are obtained. Preliminary experiments agree with persistence length values of the order of 1 meter and Young modulus around 100 MPa. On the theoretical side, the measurements represent a direct evaluation of the stiffness of semiflexible polymers based on the fluctuations of their eigenmodes. Also investigated in this study is the dependence of the rod elasticity with respect to the nanostructure and composition of the magnetic materials.

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BERRET Jean-François, CHEVRY Loudjy, GERBAL Fabien, YAN Minhao

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