Electric and magnetic field-induced birefringence of 2D nanocolloidal liquid crystals with a large magneto-optical Kerr effect

In recent years, the field-induced alignment of 2D lyotropic liquid crystals (2D LCs) has attracted increasing attention due to its promising applications in mechanical sensing, biomedicine, and optical devices. However, the mechanisms governing external field-driven assembly of 2D nanoparticles and the associated birefringence effect remain unclear. Identifying optimal material systems and field-control strategies for practical implementation remains a critical challenge. We present a systematic comparative study of electric- and magnetic-field-induced reorientation behaviors of 2D nanoparticles. We demonstrate that electric-field-induced reorientation predominantly occurs in the isotropic or biphasic states, where individual nanoparticles reorient independently. In contrast, magnetic-field-induced reorientation is most pronounced in the nematic phase, where tactoid domains exhibit a collective response to the applied magnetic field, achieving approximately four times higher birefringence than that induced by electric fields. We critically analyze the advantages and limitations of both methods and delineated their ideal application scenarios. This analysis may contribute to the design and manufacture of optical devices capable of exploiting a wide range of birefringence.