Tuning the birefringence of the nematic phase in suspensions of colloidal gibbsite platelets

We consider the birefringence patterns of nematic liquid crystals of gibbsite platelets at interfaces and in an aligning magnetic field. In solvents with a refractive index close to the particle refractive index, the intrinsic birefringence of the platelets dominates, resulting in positive birefringence, while if the solvent has a considerably different refractive index, birefringence due to the anisometric particle shape wins over the intrinsic birefringence, resulting in negative birefringence. The inversion of the birefringence leads to fascinating birefringent patterns.