Enhanced nanosecond electro-optic effect in isotropic and nematic phases of dielectrically negative nematics doped by strongly polar additive

TL;DR

This study demonstrates that doping nematic liquid crystals with a highly polar additive significantly enhances their nanosecond electro-optic birefringence effects, improving their potential for practical applications.

Contribution

The paper introduces a novel doping strategy using a strongly polar additive to substantially increase electro-optic birefringence in liquid crystals.

Findings

DPP doping increases birefringence up to 0.02 in NEMOP and Kerr effects.

Doping slows switching processes, but temperature adjustments can mitigate this.

Enhanced birefringence improves the practicality of nanosecond electro-optic applications.

Abstract

An electric field can induce or modify optical birefringence in both the isotropic and nematic phases of liquid crystals (LCs). In the isotropic phase, the electric field induces birefringence with an optical axis along the field. The phenomenon is known as the Kerr effect. In the nematic, the analog of the Kerr effect is the change of existing birefringence through nanosecond electric modification of order parameters (NEMOP) that does not require realignment of the optic axis. The utility of both effects for practical applications is challenged by a relatively weak birefringence induced by the field. We address the issue by adding a non-mesogenic additive 2, 3-dicyano-4-pentyloxyphenyl 4'-pentyloxybenzoate (DPP) with a large transverse dipole moment to mesogenic materials in order to enhance their negative dielectric anisotropy. The DPP doping substantially increases the field-induced birefringence in both NEMOP and Kerr effects, up to 0.02. The doping also slows down the switching processes, but this effect can be compensated by rising working temperatures, if necessary. The enhancement of field induced birefringence by the non-mesogenic dopant paves the way for practical applications of nanosecond electro-optic effects.