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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 (TNI) 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 π-π 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.

Doping of ferric oxide (Fe2O3) nanoparticles in 4-octyloxy-4ʹ cyanobiphenyl (8OCB) liquid crystal compound embedded in sample cells formed by photolithographic technique. The dielectric spectroscop...

In this study, we have investigated the electrical and anchoring energy of ferroelectric liquid crystal (FLC) with the dispersion of SiO2 nanoparticles (NPs). Due to their higher average spontaneou...

Herein, we have discussed change in dielectric and optical properties due to dispersion of Strontium hardystonite (Sr-HT) in the pure nematic liquid crystal (LC). The two different (0.5% wt./wt. and 1.0% wt./wt.) concentration of Sr-HT are dispersed in the pure nematic LC. After the dispersion of Sr-HT we have observed faster response and lower threshold voltage in comparison to pure nematic LC. The higher value of dielectric anisotropy calculated from the dielectric measurement and it has been suggested that lower voltage is required for switching of nematic molecules. The faster response and low threshold voltage will be very beneficial for application point of view used in making flat panel displays and lower power consumption devices. The UV absorbance and optical transmittance is reduced for Sr-HT dispersed nematogen. Photoluminescence (PL) spectra suggested the shifting in emission peak for Sr-HT dispersed nematogen due to different molecular interaction taking place between nematic LC and Sr-HT molecules. In addition to this Fourier Transform Infrared Spectroscopy (FTIR) for pure and Sr-HT dispersed nematogen has also been done.

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 in...

In this work, we investigate the effect of UV light irradiation on the dielectric parameters of nematic liquid crystal (5CB) and ZnO nanoparticles dispersed liquid crystal. With addition of nanoparticles in nematic LC are promising new materials for a variety of application in energy harvesting, displays and photonics including the liquid crystal laser. To realize many applications, however we optimize the properties of liquid crystal and understand how the UV light irradiation interact the nanoparticles and LC molecules in dispersed/doped LC. The dielectric permittivity and loss factor have discussed the pure nematic LC and dispersed/doped system after, during and before UV light exposure. The dielectric relaxation spectroscopy was carried out in the frequency range 100 Hz–10 MHz in the nematic mesophase range. Keywords: Dielectric permittivity, Relaxation frequency, Nematic liquid crystal, UV light irradiation

In the present work, multiwall carbon nanotube dispersed/doped nematic liquid crystal mixture have been synthesized by ultrasonication technique and studied using dielectric spectroscopy tools in the frequency range of 10 kHz-40 MHz. We have observed that the dielectric permittivity, loss and relaxation frequency of a nematic liquid crystal (MBBA) are influenced by the presence of multiwall carbon nanotube as a function of frequency and temperature. The value of dielectric permittivity increases with the dispersion of multiwall carbon nanotube due to π-π interaction of MWCNT and LC molecules. However, an increase in relaxation frequency is also found in dispersed samples. The MWCNT with almost identical size within themselves are dispersed at 0.5% concentration into nematic LC. The MWCNT-nematic LC composites are not only of fundamental importance, but also useful materials for device applications such as liquid crystal displays.

In this work, we investigate the effect of UV light irradiation on the dielectric parameters of the nematic liquid crystal (5CB) containing dispersed ZnO nanoparticles. With addition of nanoparticl...

The present investigation on the dielectric and electro-optical properties of nematic liquid crystal (NLC) E204 and TiO2 nanocomposites has been carried out with a wide range of frequencies. The low-frequency spectra of these composites with a concentration of 0.1 wt/wt%, 0.5 wt/wt%, and 1.0 wt/wt% are recorded in the frequency range of 50–1000 Hz, and the content of impurity ions in these samples has been analyzed. The ion trapping by adsorbing sites of TiO2 and that effect on DC conductivity and diffusion constant have also been investigated. TiO2-doped LC cell results in a two-fold faster response time of the pure LC cell, as a consequence of a remarkable reduction in the rotational viscosity of the LCs. The change in the intensity of the photoluminescence (PL) spectra of NLC composites as a function of the concentration of TiO2 nanoparticles (NPs) has also been investigated. PL spectra reveal that the PL-quenching increases in nano-nematic composites with increasing the concentration of TiO2 NPs following to the Stern-Volmer quenching equation. The pure NLC exhibits a strong absorption band nearly at 314 nm, attributing to π-π* transitions in the phenyl rings which has been slightly blue-shifted after the addition of TiO2 NPs. This blue shift was to be attributed to the n → π⁎ electronic transitions in the systems. The doping of TiO2 NPs has a promising application to the field of LC devices and displays.

Dielectric and electro-optic properties of a weakly polar nematic liquid crystals (NLCs) based on polyvinyl pyrrolidone capped gold nanoparticles doping has been reported. The dielectric spectra of these composites with a concentration of 0.25 wt%, 0.5 wt%, and 1.0 wt% are recorded in the frequency range of 42 Hz to 5.5 MHz. Dielectric permittivity and dielectric loss in these samples have been analyzed for both homogeneously-aligned and vertically-aligned liquid crystal (LC) cells. It has been observed that GNPs doping significantly reduce the threshold voltage (~27%) for LC reorientation which is explained by increased dielectric anisotropy and decreased splay elastic constant of doping LC cells. Nearly 57% faster fall time is also observed as a consequence of a remarkable reduction in the relaxation time (about short molecular axis) thus rotational viscosity of the doping LC cells. GNPs doping has an auspicious application to the fields of LC devices and displays. The present work shows that the composite under investigation performs far better than the pure LC cell in the display as well as photonic applications.

Organic–inorganic composite based on liquid crystalline and TiO2 nanoparticles were obtained and investigated taking into account the crystallographic form of TiO2 i.e., anatase/rutile mixed phase. TiO2 is an important class of material having various dielectric and electro-optical properties. The existent research presents the electro-optical properties of nematic liquid crystal (NLC) E204 and TiO2 nanocomposites over an extensive range of frequencies. Various important display parameters such as response time, threshold voltage, pretilt angle and activation energy of pristine as well as TiO2 doped composites systems were measured and analyzed. In comparison with the pure, TiO2-doped composite systems has approximately 50% faster response time, owing to its remarkable decline in the relaxation time and activation energy of the LCs. The alteration in the optical intensity of the NLC composites as a function of the concentration of TiO2 nanoparticles (NPs) was also examined. It was established that the optical intensity in nano-nematic composites was decreasing with the concentration of TiO2 NPs. Also, it was observed that an escalation in the TiO2 NPs concentration in NLC composites indicates to an escalation in the birefringence. Probable mechanisms of the interactivity between NLC molecules and TiO2 NPs have been discussed. The current work shows that the TiO2 NPs doping has an encouraging application in the display devices, including other electro-optical as well as photonic applications.

In this study, UV absorption, fluorescence and electro-optical study have been performed for pure ferroelectric liquid crystal (FLC) and its three different concentrations, i.e. 1%, 3% and 5% of fl...

Herein, we investigate a hydrogen-bonded liquid crystal compound, namely 4-(Heptyloxy) benzoic acid (7OBA), and its composites by dispersing Graphene and reduced graphene oxide (rGO) flakes into an optimized concentration. The pristine 7OBA and its composites are characterized by different instrumental techniques like polarized optical microscopy, differential scanning calorimetry (DSC), dielectric, UV-visible, and Fourier-transform infrared (FTIR) spectroscopy. DSC thermograms of the 7OBA composites evince the down-shift in the smectic C−nematic and nematic−isotropic phase transition temperatures. The polarized optical micrographs (POMs) of composites reveal the homogeneous distribution of graphene and rGO flakes in the 7OBA compound without any aggregation. The π-π* transitions in phenyl ring of 7OBA compound and π-π* transitions in C C bonds of graphitic materials are superimposed to each other providing an enhanced UV absorbance nearly at 255 nm for the composites. The presence of graphene and rGO enhances the tan δ and electrical conductivity of the composites, whereas dielectric anisotropy, Δϵ, reduces as a function of temperature in comparison to the pristine 7OBA compound. The sign inversion of Δϵ has been observed for the 7OBA/rGO composite which has been explained via dipole−dipole interactions. The I−V behavior of the pristine 7OBA compound yields the ohmic I−V curve with a non-zero current at 0 V attributing to the pseudocapacitance effect, whereas, after the dispersion of graphene and rGO flakes, nonlinear diode like I−V curves having a hundred times larger conduction current were obtained. Furthermore, the molecular interactions have been analyzed by the FTIR which confirms the formation of hydrogen bonding in the 7OBA/rGO composite. At last, these experimental findings are compared with the simulated results by DFT. The experimental and theoretical simulations are commensurable to each other. The studied composites have shown their vital applications in nonlinear electronics.

Nanoparticles doped liquid crystal show changed dielectric properties in comparison to pure liquid crystals. These changes are strongly dependent on the inherent properties of guest and host particles. In the present work we have done comparative dielectric study of highly polar nematic liquid crystals 5CB and weakly polar liquid crystal D6AOB and its 1 % wt/wt concentration with zinc oxide nanoparticles (1 % Cu) doped. The relaxation modes in pure and nano doped samples are explained properly. We have also analyzed the dielectric anisotropy and relaxation frequency for all the samples.

Nanoparticles doped liquid crystal show changed dielectric properties in comparison to pure liquid crystals. These changes are strongly dependent on the inherent properties of guest and host particles. In the present work we have done comparative dielectric study of highly polar nematic liquid crystals 5CB and weakly polar liquid crystal D6AOB and its 1 % wt/wt concentration with zinc oxide nanoparticles (1 % Cu) doped. The relaxation modes in pure and nano doped samples are explained properly. We have also analyzed the dielectric anisotropy and relaxation frequency for all the samples.

The present study is dedicated to the use of tin oxide (SnO2) nanoparticles dispersed in a multicomponent ferroelectric liquid crystal (FLC) mixture with the aim of showing their effects on the textural, dielectric, thermal and optical properties. The influence of the dopant concentration on the various physical parameters of the FLC has been discussed. Formation of self assembled two dimensional arrays of nanoparticles has been observed in the planar aligned textures of composites which is oriented perpendicular to the rubbing direction. The Differential Scanning Calorimetry study confirms the change in phase transition temperature of all the composites. The relative permittivity, absorption strength and ac conductivity have been reduced in presence of the nanoparticles. The optical extinction of neat ferroelectric liquid crystal has been decreased after the addition of tin oxide nanoparticles. The quenching phenomenon was observed for nanoparticles dispersed ferroelectric liquid crystal.

10% Cu doped ZnO nanoparticles (NPs) prepared by hydrothermal and solvothermal method have been dispersed to the pure FLC 17/100 in 1% concentration of guest entity. Electro-optical, elastic and dielectric analysis has been made for the FLC-NPs composite system with the variation of temperature. The nature of the composite system clearly shows the alteration in FLC parameters with the dispersion of NPs. The interaction between crystalline NPs and non-crystalline ferroelectric liquid crystal matrix modifies the properties of the pure FLC system. The synthesis method of NPs is also responsible for the changes taking place in physical properties of the pure FLC. The size and surface defects of the NPs amend the FLC parameters like dielectric permittivity, relaxation frequency, relaxation strength, tilt angle, spontaneous polarization and rotational viscosity etc. The coupling of spontaneous polarization and tilting of the FLC molecules are factors responsible for the resultant electro-optical (E-O) parameters of the composite system.

Our intention in the present work is to find out the role of dye in the molecular orientation of the weakly polar nematic liquid crystal D6AOB. The doping of a dye introduces a disturbance in the molecular arrangement of the nematic liquid crystal molecules. However, this disturbance is found to be sensitive to the concentration of the dye dispersed in the nematic liquid crystal. It is found that orientation in the dyed nematic liquid crystal is less ordered than the orientation in the pure nematic liquid crystals. This behavior has been explained on the basis of intermolecular interaction, i.e., dipole–dipole interaction.

The dielectric measurements of a weakly polarized nematic liquid crystal (D6AOB) were carried out in the frequency range 100 Hz to 40 MHz and in the voltage range from 0 to 40 V at 100 Hz. The dielectric data were measured for two principal alignments, homeotropic and planar. The angle β between the long molecular axis and dipole moment of the molecules is calculated from Cole-Cole plots using Onsager theory, both for pure and doped liquid crystal. Here is an attempt to discuss the Δϵ v/s voltage on the basis of piezoelectric strain, which is in good agreement with experimental results.

The effect is reported of surface anchoring on various electro-optical parameters of a pure ferroelectric liquid crystal (FLC) and five mixtures with different concentrations of dye. The Anthraquinone D5 dye was used as guest entity, whereas Felix 17-000 was used as host in this investigation. The presence of dye molecules in the FLC dramatically affects the electro-optical properties compared with those of the pure system. Electro-optical parameters such as spontaneous polarization and rotational viscosity not only change with the addition of dye but they are also strongly dependent on the concentration of dye in pure FLC. The effect of dye molecules on the anchoring energy of the pure FLC system was also investigated. Due to strong anchoring energy on FLC substrate, its effect on response time was also studied. An improvement in the contrast ratio after dye doping was observed. The value of spontaneous polarization increases due to addition of dye, suggesting that molecular alignment improves, which is ...

The present paper reports sign inversion in dielectric anisotropy of a nematic liquid crystal, i.e. 5CB, as an effect of doping dye (solvent green 3) in small amount. It is the result of strong variation of the parallel component of dielectric permittivity with temperature for a dye doped sample. This behavior is attributed to the interaction taking place between the nematic liquid crystal molecule and the dye molecule. This behavior of dielectric anisotropy has been explained on the basis of interaction between the dye (guest) and the liquid crystal molecules (host).

The ferroelectric liquid crystals (FLCs) displays normally suffer from less contrast ratio and vision angle. To produce high optical contrast and colors in FLC displays, Guest-host mode is widely used. Addition of a small amount of polymer in the pure FLC results in considerable change in its dielectric and electro-optical properties. In the present paper we have investigated the effect of adding polymer (PMMA) on the FLC material (Felix 17/100). Polymer doped FLC composites (FLCPC) has been prepared by the dispersion of 1% wt/wt concentration of polymer in pure FLC. Planar aligned cells have been used to study dielectric and electro-optical properties in SmC* phase of both the samples i.e. pure FLC and FLCPC. Considerable change in various properties like spontaneous polarization, anchoring parameters, Goldstone mode relaxation time and relaxation strength have been noticed for both the samples. These changes have been explained by considering polymer network formed in the FLC matrix.

CuInS2/ZnS core/shell quantum dots (CIS/ZnS QDs) dispersed ferroelectric liquid crystal (FLC) mixtures have been characterized for their application in electro-optical devices, energy storage, and solar cells. Physical properties of the CIS/ZnS QD-FLC (ferroelectric liquid crystal) mixtures have also been investigated with varying QD concentrations in order to optimize the critical concentration of QDs in mixtures. The presence of QDs breaks the geometrical symmetry in the FLC matrix, which results in a change in the physical properties of the mixtures. We observed the reduced values of primary and secondary order parameters (tilt angle and spontaneous polarization, respectively) for mixtures, which also depend on the concentration of QDs. The reduction of spontaneous polarization in QDs-FLC mixtures is attributed to the adverse role of flexoelectric contribution in the mixtures. The 92% faster electro-optic response and enhanced capacitance indicate the possible application of these mixtures in electro-o...

The experimental results of this work point out the role of the guest dye molecules in the molecular ordering of nematic liquid crystals. We have discussed the changes in the energies of interactions between rod-like nematic molecules and anthraquinone dye by considering the presence of steric and dipole–dipole interactions in the dye-doped system. The concentration of the dye plays an important role in the determination of molecular ordering in such dye-doped systems. Below a certain concentration of dye (known as the critical concentration), where the interaction between the dye molecules can be neglected, the addition of dye molecules introduces some disorder into the system in the form of domain formation. Above this critical concentration, this disorder is small.

The present study reports the dielectric and electro-optical study of inorganic ZnO (Cu 1%) nanoparticles doped nematic liquid crystal (5CB). The dielectric permittivity is found to decrease in the nano doped sample. Nanoparticle doped liquid crystal has good response under various conditions to evaluate their potential as electro-optical materials for various purposes. From electro-optical study we have found Freedricksz transition voltage Vth and response time τ0 and hence K11 and rotational viscosity γ are also calculated. It is found that K11 and Vth increases for nano-doped sample. Rotational viscosity γ also increases for the nanoparticle doped sample. These changes have been explained in this article according to Osipov and Ternentjev theory of rotational viscosity of nematic liquid crystal.