UDC: 681.325.2

Liquid crystals can exhibit structural orientational order. The creation of a mixture with the addition of chiral
molecules to the nematic liquid crystal induces helical twisting, the axis of which is directed perpendicular to the
cell surfaces. When some cholesteric mixtures with a sufficiently short spiral pitch (up to 400-500 nm) are heated
to a temperature close to, but still lower than, the temperature of the main transition to the isotropic state, in some
cases the so-called blue phases can be formed.
We carried out a study on the detection of structural manifestations of the blue phase under the action of vapors
of chemical substances, in particular acetone. The main dependences of effect of acetone on the liquid crystal
mixture depending on the concentration were also revealed. The two-stage phase transformation from cholesteric
liquid crystal to the isotropic liquid via the intermediary blue phase could be clearly recorded by changes in optical
transmission. Possible applications are discussed.
Keywords: liquid crystal; E7; gas sensor; blue phase; optical sensor