67th Annual Meeting of the APS Division of Fluid Dynamics (November 23, 2014 — November 25, 2014)

V0043: Ferromagnetic disc in a nematic liquid crystal under the action of a magnetic field

Authors

• Alena Antipova, University of Western Ontario
• Colin Denniston, University of Western Ontario

DOI: https://doi.org/10.1103/APS.DFD.2014.GFM.V0043

Unique long-range interactions between colloidal particles in liquid crystals, that are not presented in isotropic fluids, provide opportunities for organization and manipulation of colloids and leads to strategies for formation of self-assembled structures.  We simulate (ferromagnetic) micro discs in a nematic liquid crystal. Without any external forces, a disc with perpendicular anchoring on the surface (i.e. in the real experiment the disc would be treated chemically to require liquid crystal particles to be perpendicular to the surface of the disc) aligns itself so that the surface normal is parallel to the average orientation of liquid crystal particles (frames where \(\mathbf{B}\)=0). If the magnetic field \(\mathbf{B}\) switches on (\(\mathbf{B}\) is parallel to the magnetic moment of the disc initially; magnetic field is represented by the green arrow) and then starts turning, the ferromagnetic disc reacts to it and rotates, following the field and causing a distortion in the orientation of liquid crystal particles (shown as light grey and light blue colors around the disc; the darker the color the more distorted the liquid crystal is at that point). But when the angle of rotation becomes greater than \(\pi/2\), the energy cost of the distortion in the liquid crystal becomes too high and the disc flips to end up in a position with much smaller distortion around it (the final frames of the movie). In our research we have shown that the motion of the disc and its position before and after the flip can be controlled by tuning the magnetic field and its rate of rotation. This helps explain a potential new approach for controlling the colloidal dynamics in liquid crystals and, thus, new methods for self-organization of colloidal particles, with applications to photonics, optoelectronics, chemical/biochemical sensing, and manufacturing of membranes.