Advanced Functional Materials

Cover image for Vol. 25 Issue 17

18_03/2008Cover Picture: Tuning the Rate-Dependent Stiffness of Materials by Exploiting Néel Relaxation of Magnetic Nanoparticles (Adv. Funct. Mater. 3/2008)

The effective stiffness of materials impregnated with magnetic nanoparticles can be modulated by magnetic fields if the nanoparticle Néel relaxation rates are slower than the characteristic deformation rates, report T. Alan Hatton and co-workers on p 462. Analysis indicates that the deflection of magnetic dipoles against the applied magnetic field on deformation of the material provides the energy absorption necessary for the enhanced stiffness observed in drop ball impact tests. The penetration depth, fraction of the impact energy that is absorbed by the rotating dipoles, and the effective increase in stiffness depend on the ratio of the characteristic magnetic energy density relative to the elastic energy density, and on the shape of the impacting object.

Magnetic Nanoparticles

Hybrid nanostructures with two or more nanoscale components have attracted much attention recently owing to the synergistic properties induced by interactions between the different components. Hao Zeng and Shouheng Sun give an overview on p. 391 of efforts to synthesize multicomponent nanoparticles with at least one magnetic component, and focus on our recent developments. Such nanoparticles show interesting magnetic, magneto-optical, plasmonic, and semiconducting properties, which can be modulated by interfacial interactions between different components, opening a new avenue to advanced multifunctional nanomaterials for device concepts and applications.

Sensors

Imprinted polymer films for the selective analysis of D-glucose and D-mannose can be prepared by co-electropolymerization of phenol with a 3-hydroxyphenyl boronic acid-monosaccharide complex containing D-glucose or D-mannose on a gold support. Itamar Willner and co-workers report on p. 478 that the analysis of the monosaccharides is based on a competitive electrochemical assay that employs the ferrocene-modified-monosaccharides as the redox label. Similarly, enantioselectivity is demonstrated by the imprint of D-glucose recognition sites on the polymer and the application of the redox-active indicator.

Light-Emitting Diodes

Color tuning of cyclometalated iridium phosphors can be achieved by simple tailoring of the phenyl ring of ppy (Hppy = 2-phenylpyridine) with various main-group moieties in [Ir(ppy-X)2(acac)]. This can be achieved by shifting the charge-transfer character from the pyridyl groups in traditional iridium ppy-type complexes to the electron-withdrawing main-group moieties, as shown by Wai-Yeung Wong, Dongge Ma, Todd Marder, and co-workers on p. 499. This new color tuning strategy provides access to IrIII phosphors with improved electron injection/electron transporting features essential for highly efficient, color-switchable organic light-emitting diodes (OLEDs).

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