Liquid Crystalline Tactoidal Microphases in Ferrofluids: Spatial Positioning and Orientation by Magnetic Field Gradients

Macroscopic manipulation of self-assembly in lyotropic systems, such as chiral nematic liquid crystals formed by cellulose nanocrystals, is kinetically hindered by the similarity between isotropic and anisotropic phases in composition and physical properties. By creating a significant difference in volumetric magnetic susceptibility between discrete liquid crystalline tactoids and continuous isotropic phases (based on the exclusion effects of tactoids on superparamagnetic doping nanoparticles), we achieved position and orientation control of liquid crystalline tactoids by magnetic field gradients as weak as several hundred gauss per centimeter, where the movement of tactoids is determined by competition between magnetic and gravitational acceleration fields. We also undertook a preliminary examination of the trapping of a liquid crystalline phase in the potential well of a quadrupole magnetic field. This method enabled us to control the phase separation rate and configuration, as well as the orientation of director fields in both tactoids and macroscopic ordered phases.