Hybrid
Nanocomposites with Tunable Alignment of the Magnetic Nanorod Filler
- Publication date
- Publisher
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 (α-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