Effect of graphene oxide dispersion in nematic mesogen and their characterization results

Abstract

Graphene oxide is dispersed in negative dielectric anisotropy nematic liquid crystal p-methoxybenzylidene p-decylaniline (MBDA) in 0.2 wt/wt%, 0.4 wt/wt%, 0.6 wt/wt%, and 0.8 wt/wt% concentrations (abbreviated as MIX 1, MIX 2, MIX 3 and MIX 4). The paper proposes techniques to characterize and fill in the sample holder nematic–graphene oxide composites. The textures, electro-optical, dielectric as well as optical properties at 54 °C in nematic phase are investigated. X-ray diffraction result shows the particle size of graphene oxide to be 10–60 nm. The zeta potential of graphene oxide is around − 35 mV and its absolute value decreases from 31.5 mV in pure MBDA to 0.56 mV in MIX 4. Polarizing microscopy results display that MBDA and its composites in unaligned cell exhibit poor contrast with non-uniformity in bright state whereas aligned ones exhibit good contrast with uniformity. The observation reveals that switch-on time practically remains constant, while switch-off time and overall response time reduces from 25.8% (MIX 1) to 83.67% (MIX 4) and 25.69–83.074%, compared to pure MBDA. Rotational viscosity increases from 2.59 to 18.18%. The threshold voltage and splay elastic constant in pure MBDA and its composites increase from 2 to 3 V and 7.25 to 8.12 pN. Reduction in dielectric parameters has been observed. The magnitude of $$~\varepsilon {'_\parallel }$$ and $$\varepsilon {'_ \bot }$$ reduces from 44.2 to 76.1% and 24.6 to 72.8%, which shows $$\varepsilon {'_ \bot }$$ is always greater than $$\varepsilon {'_\parallel }$$. Therefore, absolute dielectric anisotropy reduces from 1.49 to 79.10%. The dielectric relaxation frequency reduces from 4.3 × 105 Hz to 2.81 × 105 Hz without bias voltage and 6.13 × 105 Hz to 2.2 × 105 Hz with bias voltage. UV–Vis absorbance study discloses π–π* transition with absorbance increase from 4.44 to 57.18% and corresponding blue shift in wavelength (249–194 nm). 7.23–65.90% quenching in photoluminescence study has been revealed. FTIR spectra are recorded on wavenumber range from 655 to 3500 cm−1. This work has application in sensors, imaging functions, improved electro-optic display devices and colorful displays devoid of color filters.