Nematic liquid crystals (NLCs) are soft-materials that combine the fluidity of liquids with the long-range orientational order of crystals. Their optical, dielectric, and elastic anisotropies make them highly responsive to external fields, which has led to their widespread use in display technologies. In the uniaxial nematic phase (N_u), molecules are oriented along a common direction, known as the nematic director. The twist-bend nematic (N_tb) phase is formed by achiral molecules, and exhibits a spontaneously chiral, self-assembled heliconical structure with a nanometer-scale pitch length. As a result of its unique properties, the N_tb phase has attracted significant attention from the research community. Nanoparticles (NPs) exhibits unique properties and behaviors, strongly influencing the properties of NLCs. The impact of NPs on an NLC system is primarily determined by their geometry, size, and chemical composition.

We conducted a comparative study of the effects of spherical, rod-like, and disk-like NPs on the electrooptical properties of a liquid crystal exhibiting both the N_u and N_tb phases. The mesogenic dimer 1'',9''-bis(4-cyanobiphenyl-4’-yl)nonane (CB9CB) was enriched with CdSe/ZnS quantum dots, hydroxyapatite nanorods, and CuFeS₂ nanoplatelets, yielding three corresponding series of LC-NP nanocomposites. The thermodynamic stability, and the ordering of the nematic phases were investigated by means of polarized optical microscopy. The phase diagrams of the nanocomposites as a function of temperature (T) and the NP mass fraction (χ) were constructed. The birefringence of the nematic phases and the conical tilt angle of the heliconical structure were determined and analyzed. The voltage threshold for the reorientation transition of both nematic phases, as well as the switching times of the N_u​ phase, were measured as functions of T and χ.