Threshold voltage decrease in a thermotropic nematic liquid crystal doped with graphene oxide flakes.

Mateusz Mrukiewicz,Rafał Mazur,Krystian Kowiorski,Paweł Perkowski,Małgorzata Djas

doi:10.3762/bjnano.10.7

Abstract

We report a threshold voltage decrease in a nematic liquid crystal compound, 4-cyano-4′-pentylbiphenyl (5CB), doped with graphene oxide (GO) flakes at a concentration of 0.05–0.3 wt %. The threshold voltage decrease was observed at the same concentration in electro-optic and dielectric spectroscopy measurements. The effect is related to the disrupted planar alignment due to the strong π–π stacking between the 5CB’s benzene rings and the graphene oxide’s structure. Additionally, we present the GO concentration dependence on the isotropic–nematic phase transition temperature, electric anisotropy, splay elastic constant, switch-on time, and switch-off time. The shape and dimensions of the GO flakes were studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The influence of the GO concentration on the physical properties and switching process in the presence of the electric field was discussed.

Highlights

Liquid crystals (LCs) are classified as a type of soft matter which are characterized by anisotropic molecules and a liquidlike fluidity behavior
The influence of the graphene oxide (GO) flakes on the quality of alignment in the planar oriented liquid crystal cells was studied by observation of liquid crystal textures using the polarizing optical microscope (POM) technique
According to the classical Michel–Levy interference color chart [38], we observe a slight decrease in birefringence of GO composites compared with the pure 5CB nematic liquid crystal (Figure 3a)

Summary

Introduction

Liquid crystals (LCs) are classified as a type of soft matter which are characterized by anisotropic molecules and a liquidlike fluidity behavior. Of all LC phases, special attention is paid to the nematic liquid crystal (NLC) phase because is widely used in many electro-optical applications [1,2]. An applied electric field can change the director orientation thereby causing a change in the optical properties. The field-induced reorientation of the LC director is known as the Frédericksz effect [3]. In the Frédericksz effect, the deformation of a homogeneous layer of a NLC is caused by the electric field E, which is initially perpendicular to the director. Such structural transition appears at a certain magnitude called the threshold voltage, Uth. When the Beilstein J.

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Conclusion