Mesomorphic, optical, dielectric, elastic and viscous properties of multi-component isothiocyanato mixtures

Abstract

Four nematic mixtures A, B, C and D, comprising alkylphenylethylphenyl isothiocyanates, alkylcyclohexylphenylisothiocyanates, biphenyl and terphenyl derivatives, respectively, were prepared and their physical properties investigated, including birefringence, static permittivity, dielectric anisotropy, splay elastic constant and rotational and bulk viscosity. All the mixtures exhibited a broad nematic range (∼100°C), moderate birefringence (Δn ∼0.23–0.26), positive dielectric anisotropy (Δε ∼ 8–10) and low rotational viscosity. The mixtures showed improved performance in birefringence and viscosity properties in comparison with the widely used commercial mixture E7. As far as display performance is concerned, mixture D was found to be the most valuable. A comprehensive study of the usefulness of the biphenyl and terphenyl derivatives as dopants in mixtures has also been conducted with a view to improving their physical parameters to give faster electro-optical response times in liquid crystal display devices. Application of these mixtures is envisaged in high-speed photonics and liquid crystal display devices.

Keywords:

• fluorinated isothiocyanated bi- and terphenyls
• multi-component mixtures
• birefringence
• static permittivity
• splay elastic constant
• rotational viscosity