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Dielectric relaxation behaviour of liquid crystals with opposite orientation of -COO ester group in molecular core

100%

Rutkowska J. , Perkowski P. , Piecek W. , Raszewski Z. , Kędzierski J.

tom Vol. 16, No. 3

262-266

Dielectric measurements were performed for two smectogens, being structurally analogous with the opposite space orientation of the -COO ester group in the molecular core, using a HP4192A impedance analyser. Gold coated electrode cells of different thicknesses were used. Temperature dependences of the relaxation frequency fR and the inverse of the dielectric strength Δ ε '⊥⁻¹ obtained by fitting experimental values of perpendicular components, i.e., the real ε '⊥ and the imaginary ε "⊥ parts of the complex dielectric permittivity to the Cole-Cole equation as well as the investigation of modification of relaxation processes under bias were determined for the SmC*, SmA*, and N* phases of studied compounds. One can conclude, on the basis of the above results, that dielectric relaxation processes observed by us in the studied compounds are similar to those of the soft and Goldstone mode typically observed by others in the SmC*, SmA*, and N* phases. It is concluded from a comparison of their properties with other related compounds that the link between the biphenyl moiety and –COO ester group is closely related to the stability of smectic phases.

Dielectric properties of ferroelectric liquid crystalline material with chiral nematic phase

75%

Wojciechowski M. , Bąk G. W. , Tykarska M.

tom Vol. 36

77--86

The ferroelectric liquid crystal with nematic N* phase has been investigated using broadband low frequency dielectric spectroscopy. The dielectric relaxation modes related to a ferroelectric Goldstone mode were detected only in a narrow temperature range. Well defined relaxation process was detected in the SmB* phase at about 90 Hz.

Dielektryczne badania ferroelektycznego związku ciekłokrystalicznego 1H3R z nematyczną fazą chiralną przeprowadzono w obszarze niskich częstości. Procesy relaksacyjne zarejestrowano jedynie w fazie ferroelektrycznej (mode Goldstona) oraz w fazie SmB* w obszarze częstości 60÷90 Hz. Przedstawiono charakterystyki zarejestrowanych procesów relaksacyjnych.