Role of Graphene Quantum Dots in Tuning the Electro-optical and Dielectric Properties of Polymer-Dispersed Liquid Crystal Films

Abstract

The role of graphene quantum dots (GQDs) in the performance of polymer-dispersed liquid crystal (PDLC) films was systematically investigated. The PDLC films were fabricated using the polymerization-induced phase separation (PIPS) technique, and the effects of GQD incorporation on the morphological, electro-optical (E-O), and dielectric properties were analyzed using polarizing optical microscopy (POM), scanning electron microscopy (SEM), an E-O setup, and a precision impedance analyzer (PIA). The incorporation of GQDs in liquid crystal (LC-HPC) from 0.1 wt % to 0.8 wt % was found to affect the LC droplet morphology and the overall performance of the PDLC films. Among all compositions, the film doped with 0.2 wt % GQDs exhibited the optimized E-O performance, where the saturation voltage (Vsat) decreased from 35 to 29.4 V and the response time (RT) improved from 4.44 to 3.04 ms compared to the undoped film. The contact angle value increased from 24.6° for the undoped film to 27.4° for the film with 0.2% GQD loading. Simultaneously, a comparatively high contrast ratio (CR) of 258 was maintained. The stability test performed for the undoped and optimized PDLC films showed that the optimized film still gives lower values of Vsat (34.6 V) and RT (3.58 ms) than the undoped film at 20,000 switching cycles. Dielectric studies revealed that the dielectric constant (ε′) increased from 4.52 to 5.97 (at 1 kHz), while the relaxation time (τ) decreased from 6.17 to 1.88 ms with the incorporation of 0.2 wt % GQDs. In addition, the dc conductivity (σdc) increased from 7.83 × 10–9 to 3.70 × 10–8 S/m. These results demonstrate the potential of GQD-incorporated PDLC films for advanced smart window and E-O device applications.