title: Physical properties of aqueous suspensions of goethite (alpha-FeOOH) nanorods. Part I: In the isotropic phase.
abstract: Depending on volume fraction, aqueous suspensions of goethite (alpha-FeOOH) nanorods form a liquid-crystalline nematic phase (above 8.5%) or an isotropic liquid phase (below 5.5%). In this article, we investigate by small-angle X-ray scattering, magneto-optics, and magnetometry the influence of a magnetic field on the isotropic phase. After a brief description of the synthesis and characterisation of the goethite nanorod suspensions, we show that the disordered phase becomes very anisotropic under a magnetic field that aligns the particles. Moreover, we observe that the nanorods align parallel to a small field (< 350 mT), but realign perpendicular to a large enough field (> 350 mT). This phenomenon is interpreted as due to the competition between the influence of the nanorod permanent magnetic moment and a negative anisotropy of magnetic susceptibility. Our interpretation is supported by the behaviour of the suspensions in an alternating magnetic field. Finally, we propose a model that explains all experimental observations in a consistent way.
authors.affiliation: Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris-Sud, 91405, Orsay, France.
authors.forename: B J
authors.initials: BJ
authors.lastname: Lemaire
authors.forename: P
authors.initials: P
authors.lastname: Davidson
authors.forename: J
authors.initials: J
authors.lastname: Ferré
authors.forename: J P
authors.initials: JP
authors.lastname: Jamet
authors.forename: D
authors.initials: D
authors.lastname: Petermann
authors.forename: P
authors.initials: P
authors.lastname: Panine
authors.forename: I
authors.initials: I
authors.lastname: Dozov
authors.forename: J P
authors.initials: JP
authors.lastname: Jolivet