Effect of the surfactant Span80 on the electro-optical properties of polymer-dispersed liquid crystal gratings

Polymer/liquid crystal (LC) composites represent a class of advanced materials for optical modulation, leveraging externally controlled refractive index changes. Among these, polymer-dispersed liquid crystal (PDLC) gratings have emerged as a promising device, where the alignment of LC molecules can be electrically controlled to modulate the grating’s diffractive efficiency. However, conventional PDLC gratings face critical limitations, including low diffractive efficiency and high driving voltages. In this study, the surfactant, sorbitan monooleate (Span80)), was doped into PDLC gratings to investigate its concentration-dependent effects on electro-optical properties. Experimental results demonstrate that doping with 1.4 wt% Span80 significantly enhances the diffractive efficiency from 18.8% to 84.7%, while reducing the driving voltage required for maximum efficiency from 1.7 V to 1 V. Contact angle measurements of polymer composites doped with Span80 (0–2 wt%) using a surface tension analyser showed that the addition of surfactant altered the polymer interfacial anchoring properties. Polarising optical microscopy (POM) and scanning electron microscopy (SEM) observations reveal that the improved performance originates from enlarged LC droplets and reduced anchoring energy at the polymer–LC interface. These modifications resulted in smoother interfacial morphology and more complete phase separation. This work provides a practical strategy for optimising PDLC-based tunable photonic devices.