MY LIQUID CRYSTAL'S LABORATORY
MY LIQUID CRYSTAL'S LABORATORY


  1. Effect of rotation of single crystal at the top of a nematic droplet (Lehmann-type effect)


    2. Recently, for the first time the dynamics of a cholesteric phase induction was investigated on dissolution of the single crystals (various chiral compounds) at the nematic droplet ("Life" of the nematic droplet [download movie 1]);and the new effect of the crystal rotation has been discovered.

    Scheme of observation of the effect of rotation of small single crystal:




    During dissolution of a single crystal of chiral compounds at the top a nematic droplet the correlation between the rotation direction and screw sense of the cholesteric helix was found:


    1. for right-handed chiral compounds the clockwise rotation of a single crystal at the top a nematic droplet is observed in polarizing microscope[download movie 2];



  2. for left-handed chiral compounds the counterclockwise rotation of a single crystal of chiral compounds at the top a nematic droplet is observed in polarizing microscope [download movie 3].

It was experimentally shown, that the angular velocity of the rotation of crystal of the chiral dopant dependent on:

  1. the crystal dimensions;
  2. helical-twisting power (HTP) of the dopant;
  3. viscosity of the nematic solvent.

For non-chiral dopants or dissolution in isotropic solvents (or isotropic phase of nematic) no rotation was observed under the same conditions. Dissolution of a single crystal of non-chiral compounds at the nematic droplet [download movie 4];


In addition, it was found, that dissolution of a single crystal of racemic mixture of enantiomers at the top a nematic droplet occurs without rotation. [download movie 5];



For systematic series of dopants (e.g., cholesterol esters), the angular velocity was:

  • proportional to the helical-twisting power;



    with different nematic matrices, the observed angular velocity was:


  • proportional to the rotational-viscosity coefficient γ1.



    It can be argued that the obtained results:

  • suggest a novel method for the evaluation of the helical-twisting power, especially useful for dopants of weak chirality,

    and

  • there are a direct evidence of transformation of the energy of chiral interactions into the energy of the molecular movement

    • 5.Cano-Grandjean texture in crossed polarisers [download movie 6].

    6.Schlieren texture of nematic with two point defects in crossed polarisers [download movie 7].



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