title: Magnetite nanorod thermotropic liquid crystal colloids: synthesis, optics and theory.
abstract: We have developed a facile method for preparing magnetic nanoparticles which couple strongly with a liquid crystal (LC) matrix, with the aim of preparing ferronematic liquid crystal colloids for use in magneto-optical devices. Magnetite nanoparticles were prepared by oxidising colloidal Fe(OH)(2) with air in aqueous media, and were then subject to alkaline hydrothermal treatment with 10 mol dm(-3) NaOH at 100°C, transforming them into a polydisperse set of domain magnetite nanorods with maximal length ~500 nm and typical diameter ~20 nm. The nanorods were coated with 4-n-octyloxybiphenyl-4-carboxylic acid (OBPh) and suspended in nematic liquid crystal E7. As compared to the conventional oleic acid coating, this coating stabilizes LC-magnetic nanorod suspensions. The suspension acts as a ferronematic system, using the colloidal particles as intermediaries to amplify magnetic field-LC director interactions. The effective Frederiks magnetic threshold field of the magnetite nanorod-liquid crystal composite is reduced by 20% as compared to the undoped liquid crystal. In contrast with some previous work in this field, the magneto-optical effects are reproducible on time scales of months. Prospects for magnetically switched liquid crystal devices using these materials are good, but a method is required to synthesize single magnetic domain nanorods.
authors.affiliation: Physics and Astronomy, University of Southampton, Southampton, United Kingdom.
authors.forename: Nina
authors.initials: N
authors.lastname: Podoliak
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Buchnev
authors.forename: Dmitry V
authors.initials: DV
authors.lastname: Bavykin
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Kulak
authors.forename: Malgosia
authors.initials: M
authors.lastname: Kaczmarek
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Sluckin