Optimizing parameters in co-assembly of magnetic and semiconducting nanoparticles templated by liquid crystal phase transition

A much sought-after goal in nanofabrication via self-assembled nano-components is creating artificial materials that exhibits multifunctionality and in situ responsiveness to external stimuli. We explore the ensemble behavior of iron oxide magnetic nanoparticles (MNPs) and CdSe/ZnS quantum dots (QDs) when dispersed in electro-optically active liquid crystalline matrix. Prior research has demonstrated an enhancement in the QD emission with a small applied magnetic field, a result of synergistic interactions between nanoparticles. In this work, the phase space is expanded by varying the sizes and relative proportions of QDs and MNPs in the assemblies. The aim is to determine the limits of sensitivity as a function of MNP size while keeping the relative concentration within a narrow range. We use 20 nm, 10 nm and 5 nm MNPs with 6 nm QDs and find that while the emission enhancement is observed for all, the reversibility is absent in the 20 nm MNP co-assembly. Transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal that the co-assemblies have QDs at the center with MNPs dispersed more uniformly, and the rotation of MNPs in an applied field may be the driving mechanism behind the observed effect.