Polymer-dispersed liquid crystals (PDLCs) stand at the intersection of polymer science and liquid crystal technology, offering a unique blend of optical versatility and mechanical durability. These composite materials are composed of droplets of liquid crystals interspersed in a matrix of polymeric materials, harnessing the optical properties of liquid crystals while benefiting from the structural integrity of polymers. The responsiveness of LCs combined with the mechanical rigidity of polymers make polymer/LC composites-where the polymer network or matrix is used to stabilize and modify the LC phase-extremely important for scientists developing novel adaptive optical devices. PDLCs have garnered significant attention due to their ability to modulate light transmission properties, making them ideal candidates for applications ranging from smart windows and displays to light shutters and privacy filters. The incorporation of different ferroelectric, thermoelectric, magnetic, and ferromagnetic nanoparticles, quantum dots, nanorods, and a variety of dyes in the PDLC matrix has gained momentum over a span of few decades, as it lowers the otherwise-required high operating voltage and reduces the electro-optical response time of these devices. Due to better contrast in the transmittance of these materials in the field-off and on states, they find extensively wide application in a variety of photonic applications, viz., optical shutters and smart windows, photorefractives, modern displays, microlens arrays encompassing polymer-gravel lenses, and many other. Since the functional parameters of these devices embrace the thermophysical attributes of PDLC networks, it therefore becomes necessary to perform a detailed analysis of the properties of PDLCs and their ameliorations upon the addition of different dopants. This Review aims to review the recent advances in PDLCs and their enrichment in terms of their performance parameters upon the addition of a variety of dopants, as well as the improvement of different photonic applications owing to superior parametric implementation of these networks.

In this paper, we investigate a commercial nematic liquid crystal (LC) mixture namely E7 dispersed with small concentrations of multi-walled carbon nanotubes (MWCNTs). The dielectric and electro-optical characterizations have been carried out in the homogeneously and vertically aligned LC cells. The electro-optical response of LC molecules has been enhanced by 60% after the addition of MWCNTs, which is attributed to the reduced rotational viscosity in the composites. MWCNTs act like barricades for ionic impurities by reducing them up to ∼34.3% within the dispersion limit of 0.05 wt%. The nematic–isotropic phase transition temperature (T${}_{NI}$) of the E7 LC has also been shifted towards the higher temperature, resulting in a more ordered nematic phase. The enhanced birefringence and orientational order parameter in the LC-MWCNTs are attributed to $\pi$-$\pi$ electron stacking between the LC molecules and the MWCNTs. The outlined merits of the LC-MWCNTs composites evince their suitability for ultrafast nematic-based electro-optical devices.

In present work, Cu:ZnO nanoparticles (NPs) used to disperse in pure nematic liquid crystal N-(4-methoxybenzylidene)-4-butylaniline (MBBA). Due to their larger dipole moment of NPs have stronger interactions with the liquid crystal molecules which lead to enhance the ordering of the nematic molecules as demonstrated by the increase in the value of mean dielectric permittivity. The dispersion of Cu:ZnO NPs on the dielectric behavior and activation energies as a function of temperature and frequency has studied for various concentrations of Cu:ZnO NPs. The complex dielectric permittivity and the relaxation frequency are dependent on the concentration of Cu:ZnO NPs. Theoretically obtained activation energy and relaxation times (Slater’s perturbation equations) have been found in good agreement with experimental results. An effort has been made to explain these results on the basis of interaction between nematic molecules and NPs.

The effect of biowaste porous carbon nanoparticles (PCNPs) on the dielectric and electro-optical properties of nematic liquid crystal (LC) mixture (1823A) of 4-(4-alkyl-cyclohexyl) benzene isothiocyanates and 4-(4-alkyl-cyclohexyl) biphenyl isothiocyanates has been studied. The dielectric permittivity of nematic LC has been increased with the dispersion of carbon NPs. The dielectric anisotropy has been calculated and found to be decreased with the dispersion of PCNPs into the pure nematic LC. The response time and birefringence have been also observed with the variation of temperature, frequency as well as the concentrations of carbon NPs. After the dispersion of PCNPs achieved better birefringence and faster response in the dispersed system, which is the significant application in display devices. Threshold voltage splay elastic coefficient and rotational viscosity have been calculated for both pure and NPs dispersed nematic system. Its value is increased with the dispersion of NPs. Additionally, photoluminescence and figure of merit have investigated as a comparative study of nematic matrix as well the dispersed system. The experimental results have been found to have good agreement with the theoretical data of nematic LC. An effort has been made to explain these experimental results on the basis of interaction between nematic molecules and carbon NPs.