2D interactions and binary crystals of dipolar and quadrupolar nematic colloids |
  Microscopic image of mixed dipolar-quadrupolar 2D lattice of 4 micron particles in a nematic liquid crystal cell (a), together with schematic presentation (b). | Janus colloidal microspheres have two hemispheres, which align the nematic liquid crystal in two different ways. We study the behavior of Janus colloidal particles in the nematic liquid crystal 5CB. Using polarizing optical microscopy, we report on different equilibrium orientations of Janus particles and different director field configurations around them depending on the preparation technique of homeotropic (DMOAP) and planar (Au) hemispheres. Using laser tweezers we measure the strength of interaction between different orientations of Janus nematic colloids, showing a boojum type of interaction in the case of DMOAP/Au capped colloids and dipolar like attraction for Au/DMOAP capped colloids, however with much lower binding energies. Of particular interest is the existence of a novel cofiguration, called a boojum-ring, characteristic of Au/DMOAP Janus nematic colloids that is also predicted within the Landau-de Gennes theory for patterned colloidal particles with competing homeotropic and planar anchoring strengths.The symmetry of the elastic interaction between the dipolar and quadrupolar colloidal particles in the nematic liquid crystal leads to a novel variety of two-dimensional nematic "binary" colloidal crystals, which have not been observed in any colloidal system. The dipolar-quadrupolar interaction is highly anisotropic and shows a power-law dependence when the particles approach each other along the director field with a pair-binding energy of the order of several thousands of kBT for 4 µm diameter colloidal particles. |
| OGNYSTA, U., NYCH, Andriy, NAZARENKO, Vassili, MUŠEVIČ, Igor, ŠKARABOT, Miha, RAVNIK, Miha, ŽUMER, Slobodan, POBERAJ, Igor, BABIČ, Dušan. 2D interactions and binary crystals of dipolar and quadrupolar nematic colloids. Phys. rev. lett., 2008, vol. 100, no. 21, 217803. |
