Electrically controlled topological micro cargo transportation

Abstract

We demonstrate electrically controlled linear translation and precision positioning of a colloidal particle in a soft matter device.

Hydrodynamics of fringing-field induced defects in nematic liquid crystals

“…Interdigitated electrodes are widely employed in In-Plane Switching (IPS) displays, with a typical electrode pitch of ∼ 12 µm, in excess of the cell gap 10 . Disclinations induced by fringing-fields due to interdigitated electrodes have been observed experimentally with homeotropic 11,12 , in-plane 13 and hybrid 14 alignments as well as predicted theoretically 15,16 . Lindquist 11 demonstrated a phase grating formed by interdigitated electrodes with an electrode-pitch of 8 µm and reported the successful fabrication of a 0.8 µm device.…”

“…Proposed applications include reconfigurable diffraction gratings 11,17,18 and fast switching displays 13,19 with typical 13 electrode-pitches of 8 µm or less. Additionally, such disclinations can be used to reconfigure liquid crystal colloids 14,20 .…”

“…Defect networks induced by topologically patterned substrates have been shown to trap particles and are reconfigurable by external fields, affording control over particle position 23 . Recently, this trapping and positional control has been demonstrated by electrically induced defects due to crossed electrodes 24 and interdigitated electrodes (with hybrid alignment) 14 . Bacteria immersed in lyotropic liquid crystals can similarly be trapped and transported by defects 25 .…”

Oblique light incidence method to study topological defects in nematic layers with conical boundary conditions

“…However, an electric field or a combination of the electric and magnetic fields applied to the LC causes a formation of point defects 26 , 27 , two-dimensional defects 28 – 30 , or soliton-like structures in the chiral nematic 31 . At homeo-planar boundary conditions, the point or linear defects can form at the substrate with planar anchoring 32 – 35 . The conical boundary conditions (the tilt angle different from 0° and 90° and the azimuthal orientation of the director is degenerate) are the most favourable concerning the diversity of forming defects.…”

Light-Induced Structures and Microparticle Transportation in a Free-Surface Frustrated Chiral Nematic Film

“…In the field of microscopic object manipulation, a lot of attention has been paid to the electrically induced transport phenomena in nematic liquid crystals, based on electrophoresis and electro-osmosis, electrohydrodynamic convection or backflow powered by director reorientations [4][5][6][7]. The presence of either artificially placed or self-generated wall defects allows the microparticles to exhibit a rich set of motions and provide control of their velocity [8,9]. A biotechnological approach involves the use of living liquid crystals, namely swimming bacteria placed in a passive lyotropic chromonic LC and pushing cargo along the trajectory defined by the nematic LC director field [10,11].…”