Nanotechnology for purifying nematic liquid crystals based on magnetic separation accompanied by phase transition.

Free ions are generally unfavorable in liquid crystal (LC) displays, and LC purification technologies are critically important. The colloidal γ-FeO magnetic nanoparticles coated with oleic acid (γ-FeO@OA MNPs) have a high ratio of surface to volume, which may adsorb more free ions and are uniform in the LC at room temperature. In this work, the precipitation and separation of the doped colloidal γ-FeO@OA MNPs resulting from the magnetic field accompanied by an isotropic-nematic phase transition are more efficient than in the single case of the phase transition or the magnetic field. The residual ion concentrations have decreased distinctly using the low gradient magnetic field (∇ B ∼ 2 T/m) with the phase transition. In addition, when the doped colloidal γ-FeO@OA MNPs are 0.4 % and 0.2 % by weight, the former concentrations of the residual ions and γ-FeO@OA MNPs are lower than the latter. As a result, the commercial nematic LC can be purified by this approach based on nanotechnology in our study.