Tying knots and linking microscopic loops of polymers, macromolecules, or defect lines in complex materials, is a challenging task for material scientists. We demonstrate the knotting of microscopic topological defect lines in chiral nematic liquid-crystal colloids into knots and links of arbitrary complexity using laser tweezers as a micromanipulation tool. All knots and links with up to six crossings and the Borromean rings are demonstrated, stabilizing colloidal particles into an unusual soft matter. The knots in chiral nematic colloids are classified by the quantized self-linking number, a direct measure of the geometric, i.e., Berry's, phase. These results could be applied to the knotting of macromolecules, skyrmion defects in chiral magnets and confined blue phases, and entangled vortices in superconductors.
COBISS.SI-ID: 2336868
Lasing of whispering-gallery modes in nematic liquid-crystal microdroplets, floating in water, is demonstrated. It is shown that millimolar concentrations of sodium dodecyl sulfate in water effect the orientation of liquid-crystal molecules in the microdroplet, which changes the lasing spectrum. The presence of targeted molecules in water can be monitored by simply measuring and recognizing the spectrum of light, lasing from a small liquid-crystal droplet in water.
COBISS.SI-ID: 25161255
The topology and geometry of closed defect loops is studied in chiral nematic colloids with variable chirality. The colloidal particles with perpendicular surface anchoring of liquid crystalline molecules are inserted in a twisted nematic cell with the variable ratio of thickness and the helical period. For a single colloidal particle, we observe that a single defect loop is winding around the particle, the winding pattern being more complex in cells with higher total twist. We observe that colloidal dimers and colloidal clusters are always entangled by one or several -1/2 defect loops. For colloidal pairs in pi-twisted cells, we identify at least 17 different entangled structures, some of them exhibiting linked defect loops-Hopf link. Colloidal entanglement is even richer with a higher number of colloidal particles, where we observe not only linked, but also colloidal clusters knotted into the trefoil knot. Colloidal entanglement might be important for binding of microphotonic networks based on liquid crystals.
COBISS.SI-ID: 25081127