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.

The present study is based on effect of dispersing Cd₁−_xZn_xS/ZnS core/shell quantum dots (QDs) on the memory behaviour of nematic liquid crystal 2020 with the variation of dopant concentration and applied voltage. Around 26% and 45% memory storage in QDs dispersed nematic matrix (MIX 1 and MIX 2) has been the core finding. The presence of ionic charges at low-frequency regime along with their reduction in QDs dispersed nematic matrix has been confirmed from tan δ curve. Pure nematic LC as well as nematic/QD mixtures depict volatile memory effect that depends upon concentration of QDs. The existence of memory due to storage of charge on QDs has been further confirmed from the dielectric, polarising optical micrographs and electro optical study under the influence of bias voltage. The observation of memory effect is attributed to the ion capturing and ion releasing phenomenon. The dispersion of QDs in nematic material plays an important role to enhance memory parameter by capturing and releasing the ionic charges under the application of bias voltage which has been confirmed from capacitance-voltage curve. Graphical Abstract

In the present investigation, TiO₂-doped weakly polar nematic liquid crystal (NLC) has been studied. This study mainly focuses on dielectric, electro-optical and optical properties of pure NLC and doped systems. Variation in different parameters like dielectric permittivity, dielectric loss, dielectric anisotropy and conductivity has been noticed. Permittivity of the doped system is almost the same as undoped system. With doping concentration, the ionic contribution to the dielectric loss as observed in low-frequency region has been suppressed and the shift in relaxation frequency toward higher frequency side has also been observed. The electrical conductivity and threshold voltage have been decreased with increasing concentration of nanoparticles (NPs). The continuous increase in dielectric anisotropy with increasing the concentration of NPs has also been observed. These results have been attributed to the trapping capability of free ions by TiO₂ NPs. Further, we focused on the study of photoluminescence (PL), UV absorbance and Fourier transformed infrared spectroscopy (FTIR) of pure and doped systems. The continuous increase in PL intensity without any shift in emission peak has been observed for doped systems. Enhancement in UV absorbance with increasing concentration of NPs has also been observed. The effect of NPs doping on molecular dynamics of NLC can be clearly seen by FTIR study. The results suggest that the TiO₂ NP-doped weakly polar NLC can have significant improved dielectric, electro-optical and optical properties. This makes the weakly polar NLC to be a potential candidate for many applications.

In order to fabricate efficient and superior performance liquid crystal (LC) devices, the physical parameters of the LC mesogens can be duly altered by incorporating non-mesogenic materials like quantum dots (QDs), graphene and polymers. In the present work, the effect of adding core/shell QDs in two ferroelectric liquid crystals (FLCs), along with the change in their physical properties, has been investigated. A small concentration of QDs is dispersed into the two FLCs and temperature variations of vital parameters like spontaneous polarisation (P_s), rotational viscosity, response time, relative permittivity and relaxation strength have been measured for both the FLC materials. The contrast ratio, UV–near visible absorbance as well as photoluminescence (PL) of both the mesogens have also been determined and compared. A faster electro-optical response and the induced phenomenon of PL with a temperature-dependent low-frequency relaxation mode have been observed in Felix 17/100 after the addition of QDs. The present study also provides valuable information about the interaction between QDs and the two FLC systems depending upon polarisation–field (P–E) coupling. The same dopant can interact with FLCs in dissimilar fashion if the intrinsic properties of both the FLCs are different thereby producing different modifications in their respective physical parameters. GRAPHICAL ABSTRACT

Multilayer graphene was deposited on indium tin oxide (ITO) -coated glass plates and characterized by suitable techniques. A liquid crystal sample cell was designed using graphene deposited ITO glass plates without any additional treatment for alignment. Ferroelectric liquid crystal (FLC) material was filled in the sample cell. The effect of multilayer graphene on the characteristics of FLC material was investigated. The extremely high relative permittivity of pristine graphene and charge transfer between graphene and FLC material were consequences of the enormous increase in relative permittivity for the graphene-FLC (GFLC) system as compared to pure FLC. The presence of multilayer graphene suppresses the ionic impurities, comprised in the FLC material at lower frequencies. The ionic charge annihilation mechanism might be responsible for the reduction of ionic impurities. The presence of graphene reduces the net ferroelectricity and results in a change in the spontaneous polarization of pure FLC. Rotational viscosity of the GFLC system also decreases due to the strong π-π interaction between the FLC molecule and multilayer graphene. The photoluminescence of the GFLC system is blueshifted as compared to pure FLC, which is due to the coupling of energy released in the process of charge annihilation and photon emission.