Small-angle scattering from spindle-shaped colloidal hematite particles in external magnetic fields

In the presence of phosphate anions, spindle-shaped mesoscale hematite particles can be prepared via controlled precipitation of iron(III) chloride. The aspect ratio of the particles is determined by the concentration of phosphate anions selectively covering specific crystal surfaces and thus enabling anisotropic growth of the particles. The scattering function for suspensions of polydisperse spindles is derived and used to analyse the small-angle scattering resulting from these particles. In the presence of an external magnetic field, the particles align perpendicular to the field direction as a result of the negative anisotropy of their magnetic susceptibility Delta(chi). Hereby, an isotropic-nematic phase transition can be induced in external magnetic fields.