Hybrid Nanocomposites with Tunable Alignment of the Magnetic Nanorod Filler

TL;DR

This study demonstrates how magnetic fields can precisely control the orientation of goethite nanorods within polymer nanocomposites, enhancing material properties for various applications by tuning nanoparticle alignment during fabrication.

Contribution

The paper introduces a method to tune nanoparticle alignment in polymer nanocomposites using magnetic fields in the isotropic phase, avoiding nematic control and enabling adjustable orientation levels.

Findings

Achieved near-perfect antinematic alignment at 1.5 T magnetic field.

Validated birefringence as a reliable measure of orientational order.

Demonstrated preservation of nanoparticle alignment after field removal.

Abstract

For many important applications, the performance of polymer-anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite ({\alpha}-FeOOH) nanorods, we produced goethite-poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1-5.5 vol \%), we used the orientational order induced by the field in the isotropic phase rather than the spontaneous orientational order of the nematic phase. At the strongest field values (up to 1.5 T), the particles exhibit almost perfect antinematic alignment, as measured by optical birefringence and small-angle X-ray scattering. The results of these two techniques are in remarkably good agreement, validating the use of birefringence measurements for quantifying the degree of orientational order. We also demonstrate that the ordering induced by the field in the isotropic suspension is preserved in the final material after field removal. This work illustrates the interest, for such problems, of considering the field-induced alignment of anisotropic nanoparticles in the isotropic phase, an approach that is effective at low filler content, that avoids the need of controlling the nematic texture, and that allows tuning of the orientation level of the particles at will simply by adjusting the field intensity.