Determination of optical and dielectric parameters of cholesteric liquid crystals: the study on chiral dopant concentration effect

In this study, optical and dielectric parameters of cholesteric liquid crystals were investigated. 4-pentyl-4′-cyanobiphenyl nematic liquid crystal and 4′-[(S)-2-methylbutyl]biphenyl-4-carbonitrile right-handed chiral dopant materials were used in the preparation of cholesteric liquid crystals. Furthermore, so as to determine the influence of chiral dopant, three samples were formed by combining 4-pentyl-4′-cyanobiphenyl and 4wt.%, 8wt.%, and 16wt.% 4′-[(S)-2-methylbutyl]biphenyl-4-carbonitrile. Optical parameters, such as wavelength-dependent transmittance and absorbance, were obtained with Ultraviolet/Visible spectroscopy. Dielectric parameters were also determined with dielectric spectroscopy. An increase in the value of dielectric constant for 1 kHz from 4.486 to 5.774 was observed with the increasing 4′-[(S)-2-methylbutyl]biphenyl-4-carbonitrile concentration. Moreover, an increase in optical band gap value from 3.791 to 3.801 eV was seen with increasing 4′-[(S)-2-methylbutyl]biphenyl-4-carbonitrile concentration. Results indicated substantial changes in optical and dielectric parameters depending on chiral dopant concentration. In this regard, it is considered that current study will contribute insight to scientists who continue their research on optical and dielectric characterizations of cholesteric liquid crystal-based composites and its technological applications.