Dielectric Properties of Compounds Creating Dual-Frequency Nematic Liquid Crystals

Abstract

In this paper we report how dielectric spectroscopy can help in creating of dual-frequency nematic liquid crystals. Dual-frequency nematic liquid crystals is new class of liquid crystal materials. Such mixture is usually formed by a combination of many components (even more than 10), which can be split into two groups: molecules having large transverse dipole moment and molecules with a large longitudinal dipole moment. The behavior of a base (parent) mixture, functional admixtures and nal dual-frequency nematic liquid crystals mixture is investigated by dielectric spectroscopy in wide frequency (100 Hz10 MHz) and temperature ranges. This allows us to nd out why the dual-frequency liquid crystal has an important feature: positive and negative dielectric anisotropy at dierent frequencies. We present parameters of molecular motions around short (S-mode) and long (L-mode) molecular axes observed in investigated materials and discuss how the creation of nal dual-frequency nematic liquid crystals mixture can modify molecular relaxations.

Dielectric behaviour of binary dual-frequency nematics with low crossover frequencies

“…They are composed of two or more similar types of molecules with parallel dipole moments (μ || ). [13][14][15][16][17] Therefore, dielectric results for AM and SCD can be similar. [13,14] Figure 2b depicts the dielectric properties of SCD.…”

“…In multi-component BM, it is definitely lower (below -60°C) than in SCB, [13][14][15][16][17] due to the fact that in multi-component BM usually special dopants are added to enhance mesophase. [16] In SCB, crystallisation temperature slightly depends on the alignment.…”

“…These molecules are components of dual-frequency mixtures previously investigated. [13][14][15][16][17] Weight percentages of individual molecules in BDFNLCs are presented in Table 1.…”

“…• a wide temperature range (crystallisation temperature below -70°C), [13][14][15][16][17] • visible molecular rotations around long (L-mode) and short (S-mode) molecular axes, [13][14][15][16][17] • a quite broad phase transition from the isotropic phase to the nematic phase (it takes ca. 10°C), [13][14][15][16][17] • a positive dielectric anisotropy above 0°C at low frequency, but below 0°C Δε is positive at high frequency, [13][14][15][16][17] • too high crossover frequency at room temperature (ca.…”

“…10°C), [13][14][15][16][17] • a positive dielectric anisotropy above 0°C at low frequency, but below 0°C Δε is positive at high frequency, [13][14][15][16][17] • too high crossover frequency at room temperature (ca. 5-10 kHz), [13][14][15][16][17] To reduce the crossover frequency and make phase transition (Izo-N) sharp, binary dual-frequency nematic liquid crystals (BDFNLCs) were created. BDFNLCs are composed of two types of molecules with μ ⊥ and μ || , respectively.…”