Effect of gelation on the Frank elastic constants in a liquid crystalline mixture exhibiting a twist bend nematic phase

The random gel network fibers formed in the nematic phase develop into directional microstructures in the twist bend nematic.

INFLUENCE OF 4- (N-ALKYL)- AND 4-(N-ALCOXY)-3′,4′-DICYANODIPHENYLOXIDES ON DIELECTRIC PROPERTIES OF LIQUID CRYSTALLINE MIXTURE OF CYANOBIPHENYLES

The mesomorphic and dielectric properties of 4- (n)-alkyl-, 4- (n)-alkoxy-3′,4'-dicyanodiphenyloxides (n = 4.5.8) solutions in the liquid crystalline mixture on the base of nematic 4- (n) -alkoxy-4'-cyano-biphenyls (n = 3,4,5,6,7,8) (CB-6) were studied. The enlightenment temperatures of the mixtures were measured by the polarization microcoscopy. The introduction of the nonmesogens was shown to result in a decrease in the enlightenment temperatures of mesomorphic compositions. The slopes of the boundary lines of coexisting nematic and isotropic liquid phases were calculated which characterized the effect of the additive on the stability of the mesophase. It is shown that the destabilizing effect of substituted diphenyloxides with respect to the thermal stability of the mesophase is affected by the feature of the substituted dicyanodiphenyloxides non-linear structure. The geometry of the investigated dopants molecules was optimized using quantum chemical calculations by the DFT method. Calculations have shown a non-linear form of diphenyloxide molecules, in contrast to the rod-like shapes of alkyloxycyanobiphenyls molecules. The components of the static dielectric permeability (ε) in nematic and isotropic phases of the compositions were measured at a parallel (ε||) and perpendicular (ε^) orientation of the sample in the magnetic field as a function of the temperature and concentration of the additives , and the dielectric anisotropy Δε = ε||- ε^ was calculated. The addition of polar dicyanodiphenyldioxides into the mesomorphic composition results in an increase in the dielectric constants. An increase in the dielectric anisotropy of liquid crystalline mixtures with an increase in the additive concentration is the most effective for homologues with short alkyl fragments. It is shown that the growth of permeability anisotropy can be associated both with the rise in the effective dipole moment of the mesophase at high polar dopants introduction and the change in the degree of the dipole-dipole antiparallel association of cyanosubstituted compounds. To estimate the correlation degree of polar molecules, the Kirkwood parameter values were calculated. The doping of the mixture CB-6 with 4-(n)-alkyl-, 4-(n)-alkoxy-3', 4'-dicyanodiphenyloxides is accompanied by a decrease in the Kirkwood factor due to the possible formation of liquid crystal-dopant associates in the compositions.Forcitation:Novikov I.V., Aleksandriiskii V.V., Maizlish V.E., Abramov I.G., Burmistrov V.A. Influence of 4- (n-alkyl)- and 4-(n-alcoxy)-3′,4′-dicyanodiphenyloxides on dielectric properties of liquid crystalline mixture of cyanobiphenyles. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 10. P. 42-46