Interactions of micro-rods in a thin layer of a nematic liquid crystal |
Topological properties of a nematic liquid crystal in the vicinity of small cylindrical objects (micro-rods), dispersed in the nematic liquid crystal are interesting for possible applications in assembling 3D log-pile photonic crystals. Depending on the type of liquid crystal anchoring on the surfaces of glass micro-rods, we have observed two types of the symmetry in the surrounding ordering of liquid crystal molecules: dipolar and quadrupolar. Using the manipulation of micro-rods with laser tweezers, the strength and separation dependencies of various pair interaction potentials have been determined. Our results are in qualitative agreement with previous theoretical predictions for 2D interactions of micro-rods in the nematic liquid crystals. |
  SEM image of 1.5 ?m thick glass micro-rods. |
 (a–c) Micro-rods of dipolar symmetry. (a) A dipolar micro-rod with homeotropic surface anchoring in a 3 ?m thick planar cell of 5CB, as observed under a non-polarizing optical microscope. (b) When a red-plate is inserted, the differently colored regions of the birefringent nematic indicate different orientations of the liquid crystal molecules. (c) The director pattern, as reconstructed from the color image (b). (d–f) Quadrupolar micro-rods in a planar cell. (d) Unpolarized micrograph of a micro-rod, which was spontaneously oriented perpendicularly to the rubbing direction. (e) The same micro-rod, as observed using the red-plate. (f) Schematic drawing of the director ?eld, as deduced from (d) and (e). |  Micro-rods in the homeotropic cell of nematic liquid crystal. (a) Non-polarized image and (b) polarized image with inserted red-plate. The location of the point defect is clearly visible on top of the micro-rod in (b). (c) Schematic drawing of the orientation of nematic molecules, the dark spot indicates the point defect. (d–f) The quadrupolar type of micro-rods are characterized by a loop defect encircling micro-rod in the plane of the screen. |
 MOVIE: Collinear attraction of two dipolar micro-rods with parallel topological dipoles. |  MOVIE: Side-by-side attraction of a pair of micro-rods with opposite direction of their topological dipoles. Interaction potential is of the order of several 1000 kT. |
| TKALEC, Uroš, ŠKARABOT, Miha, MUŠEVIČ, Igor. Interactions of micro-rods in a thin layer of a nematic liquid crystal. Soft matter, 2008, vol. 4, no. 12, 2402-2409. |
