Blue Phase Range Research Articles

Thermal and Electro-Optical Properties of Size Dependent Nickel Nanoparticle Doped Blue Phase Liquid Crystals

In present work, effect of nickel nanoparticles size on blue phase stabilization and its electric-optical properties has been demonstrated in In plane switching (IPS) configuration of liquid crystal cells. Variation in phase transitions and their textural behavior after doping of nickel nanoparticles of sizes 20nm and 40nm in pure blue phase liquid crystal was observed under polarizing optical microscope in IPS cells and compared the results with already reported data in indium tin oxide coated glass plate cells. Blue phase range has been widened after doping of both size of nickel nanoparticles and maximum BP range found is 6.5oC and 6.3oC in 20nm and 40nm-BPLC composites respectively in IPS cells. Voltage-transmission data has been taken for pure blue phase liquid crystal and nickel nanoparticles doped blue phase liquid crystal systems at a particular frequency and further various electro-optical parameters have been measured.

Effect of size and concentration of magnetic nanoparticles on blue phase stabilization and electro-optical properties in blue phase liquid crystalline nanocomposites

Blue phase liquid crystal material having a wide blue phase range of 7 °C was prepared in a binary mixture of nematic and chiral nematic liquid crystals with optimization of chiral dopant concentration. Magnetic nanoparticles of size 20 nm, 40 nm in varying concentrations (<0.5 wt %) could successfully stabilize the blue phase temperature range. Interestingly, the BP stability increases approximately 7.8 °C with an increase in nanoparticles concentration up to a critical concentration (0.1 wt %) and then gradually decreases at higher concentrations of nickel nanoparticles. A detailed comparative electro-optical study of pure blue phase liquid crystal and size dependent nickel nanoparticles doped blue phase liquid crystals is accomplished. The transmission of light increases up to 42–45% for nickel nanoparticles doped blue phase liquid crystal samples than pure blue phase liquid crystal with negligible residual birefringence. An increase in isotropic temperature was noticed in 40 nm nickel nanoparticles doped sample. Also an improvement in threshold voltage, induced birefringence, contrast ratio and Kerr constant with doping of nickel nanoparticles was observed. The present study is a synergistic correlation of size and concentration of nickel nanoparticles with blue phase liquid crystals and sufficiently productive for developing nanoparticles doped blue phase liquid crystal optical devices in future. • Size and concentration dependent magnetic nanoparticles stabilised blue phase liquid crystals are prepared and studied. • 7.8 °C wide BP range was observed using Ni NPs in BPLCs. • Variation in phase transition temperatures and BP range was noticed with variation in concentration and size of NPs. • An improvement in switching voltage, contrast ratio, birefringence and Kerr constant was observed by stabilization of BPLCs through Ni NPs.

Selective stabilization of blue phase liquid crystals using spherical and rod-shaped colloidal nanocrystals

Optimizing strategies used for improving the stability and properties of blue phase (BP) liquid crystals directly impact device performance. Various factors ranging from molecular structure to sample size and substrate conditions can influence selective reflection and electro-optics of BPs. More recently, the technique of incorporating colloidal nanoparticle (NP) assemblies has been used to enhance BP ranges. In cubic BPs, disclination networks can act as trapping centers for NPs, reducing the high elastic energy cost of these regions, favoring BP stability. Organization of NPs in the defect regions can sustain stable 3D colloidal structures, widening the scope and applicability of BPs as photonic materials. Physical and chemical properties, size, and shape of the NPs can also determine the utilization of BPs for advanced applications like lasers and high quality displays. In view of this, a mixture of two calamitic chiral compounds in which all three BPs, viz., BPI, BPII, and BPIII, were induced was combined with rod-shaped CdSe/CdS quantum rods (QRs) and spherical CdSe quantum dots (QDs), which were specifically chosen due to their exceptional optical properties. This also provided an opportunity to investigate the effect of the shape of the NPs on the preferential stabilization of the BPs and on the electro-optic Kerr effect. QRs were found to be more efficient in enhancing the overall BP range, with an almost twofold increase of ∼27 °C with ∼0.5 wt. %. On the other hand, with QDs, the BP range showed an initial increase of 20 °C for ∼0.3 wt. %, which, however, decreased with a further increase in QDs. Another major difference is that the Kerr effect was active only in the BPIII in the case of QDs but is measurable in both cubic BPI and BPII in the case of QRs. The results have been described in terms of the organization of the nanocrystals within the defect lines and the lattice orientations imposed by the substrates.

Blue phase stabilization by CoPt-decorated reduced-graphene oxide nanosheets dispersed in a chiral liquid crystal

We report on the effect of reduced-graphene oxide nanosheets decorated by CoPt nanoparticles on the blue phase range of a chiral liquid crystal. By means of high-resolution ac calorimetry and polarizing optical microscopy, it is demonstrated that a small concentration of these nanosheets induces the stabilization of a single blue phase structure in comparison to three blue phases existing in the pure compound. The results are compared with other liquid crystal-dispersed graphene studies, and, moreover, a short theoretical discussion of the stabilization effect is included.

Clusters of B7 Fibers Reveal Origin of Blue Phase Stability in a Binary Mixture of Chiral Rod-like and Achiral Bent-Core Molecules.

Liquid crystal (LC) blue phases (BPs) have gained relevance because of their potential applicability as tunable photonic band gap materials. However, their narrow temperature range often restricts technical usage. Doping with an LC made of achiral bent-core (BC) molecules is one of the strategies employed to increase BP stability. It is now shown that mixing a BCLC exhibiting the polarization-modulated lamellar B7 phase, with a calamitic chiral LC made of rod-like (R) molecules, enhances the BP range considerably. The special feature in this system is the spontaneous expulsion of clusters of B7 fibers in the chiral nematic (N*) phase occurring below the BPs. This gives a clear indication that islands rich in BC molecules lie interspersed between the R molecules. Based on several experimental studies, it is shown that the BP stability may be attributed to an interplay of conformational and intrinsic chirality of the BC and R molecules across the interface of these islands. This study provides new insights from a molecular point of view and provides a novel technique for designing stable-induced BPs. The additional novelty is the occurrence of a phase transition within the fibers. Further, the electro-responsive fibers may also have a potential to form new materials.

The effects of azo-oxadiazole-based bent-shaped molecules on the temperature range and the light-responsive performance of blue phase liquid crystal

ABSTRACTA series of light-responsive azo-oxadiazole-based bent-shaped molecules was synthesised and characterised. Their effects as dopants on the blue phases (BPs) range of the chiral nematic liquid crystal (N*LC) matrix and light-responsive properties including the photo-inducing change of UV absorption properties, photo-adjusting the BP structure as well as the temperature range were investigated. It was found that the azo-oxadiazole-based bent-shaped molecules with branched terminal had better miscibility in LC host than the molecules with straight terminal, and that increasing the length of rigid core of bent-shaped molecules will greatly improve the effect of widening the BP temperature range.

The effects of molecular structure and functional group of a rodlike Schiff base mesogen on blue phase stabilization in a chiral system

A wider blue phase (BP) range can be induced easily when two difluoro substituted and racemic rodlike Schiff base mesogens are doped with the appropriate concentration of chiral dopants S811 or ISO(6OBA)2.

Exploration of Induced Blue Phases and Orthogonal Smectic Batonnets in Hydrogen-Bonded Ferroelectric Nanoliquid Crystalline Complexes for Optoelectronic Devices

A novel blue phase hydrogen-bonded ferroelectric liquid crystal (HBFLC) series has been synthesized from cholesteryl stearate (CHS) and p-n-alkyloxybenzoic acid (nOBA, where n = 2 to12). Blue phase (BP) liquid crystalline complex is a high potent material for next-generation optoelectronic devices. The structural, optical, and thermal properties of present HBFLC complexes have been characterized by X-ray diffraction techniques (XRD), Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR), polarizing optical microscope (POM), and differential scanning calorimetry (DSC) techniques. The band gap energy of the present HBFLC complex (4.6 eV) is estimated by UV-Visible spectrometer. X-ray diffraction and scanning electron microscope (SEM) studies which confirm the monoclinic nature and morphology of the present complex. Phase diagram of the present CHS + nOBA is constructed from DSC data and the same is discussed. The lower homologous of CHS + nOBA HBFLC (n = 2 to 6) complex shows BPsm1, BPsm2, BPsm3 while higher homologous (n = 7 to 12) exhibiting orthogonal smectic A* (SmA*) character with blue phases. A noteworthy observation is that the identification of extended thermal span of smectic blue phases and induced SmA* phase in the present HBFLCs. Another important observation is that the widest BP range is reported in the present hydrogen-bonded ferroelectric nanoliquid crystalline (HBFNLC) complex which is more suitable for photonic devices. In addition, LC parameters such as, phase width, thermal stability factor, phase transition temperature with enthalpy value, and the origination of orthogonal phases in CHS + nOBA HBFLC complex is also reported.

Synthesis of chiral azobenzene derivatives and the performance in photochemical control of blue phase liquid crystal

ABSTRACTA series of chiral azobenzene compounds with branched terminal were synthesised, and the photosensitive performances were investigated accordingly. It was found that the photochemical properties were mainly affected by the trans–cis configuration of azobenzene and the linked position between the azobenzene and chiral centre. The para-type azobenzenes showed general photochemical decrease in helical twisting power (HTP), but the meta-type ones appeared interestingly showed photochemical increase in HTP. This work provided an effective method for designing molecules to control blue phase (BP) including adjusting colours, inducing BP and extending BP range, which was promising in the applications of optically addressable devices.

Graphene oxide modified with aminoazobenzol group stabilized blue phase liquid crystals

ABSTRACTLiquid-crystalline blue phases are stable only for very narrow temperature range between the isotropic and the chiral nematic phase that severely hinders their applicability. Herein, aminoazobenzol group was chemically grafted onto graphene oxide (GO) via amidization reaction. Successful grafting of aminoazobenzol group was confirmed using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV-vis absorption spectra and Thermogravimetric analysis (TGA). The resultant aminoazobenzol group modified GO sheets which is reduced (GO-Az) were easily redispersed in common organic solvents. By doping different contents of GO-Az nanosheets could stabilize blue phase and increase the blue phase range. When doped with 0.5 wt% GO-Az, the mixtures show the wider range with 5.4°C than the range with 3.6°C of blue phase liquid crystals without GO-Az. Meanwhile, the phase sequence and the range of the aforementioned phases are reproducible upon heating and cooling, which shows that the blue phases doped with GO-Az nanosheets are thermodynamically stable.

Electro-optics of polymer-stabilised blue phase liquid crystal in in-plane switching mode

ABSTRACTIn the present work, polymer-stabilised blue phase liquid crystal ***(PS-BPLC) that exhibit the blue phase (BP) in a temperature range of 312.15 K to 298.15 K has been prepared. The textural and electro-optic studies were performed in the BP range using an in-plane switching (IPS) cell. Platelet-type textures of cubic BP having an average domain size of ~12 µm were observed. The on-state voltage increased with increasing the temperature due to reduced value of the Kerr constant. Further, the hysteresis was found to be reduced from 19.2% to 5.1% by operating the PS-BPLC sample cell at an elevated temperature.

Wide blue phase range induced by bent-shaped molecules with acrylate end groups

Three kinds of bent-shaped molecules (A-1, A-2, A-3) were synthesized and doped into the chiral nematic host to induce blue phase. The widest induced blue phase temperature range of 48.6°C is gained for the molecules with acrylate end groups and lateral substituent CN, which has the largest biaxiality and better solubility. After ultraviolet (UV) irradiation, the blue phase range was reduced to 39.1°C, the relationship between the molecular structures and the inducing effect was discussed.

Effects of thiophene-based mesogen terminated with branched alkoxy group on the temperature range and electro-optical performances of liquid crystalline blue phases

ABSTRACTA series of symmetrically thiophene-based bent-shaped molecules with branched terminal was synthesised and characterised. Then, their effects as dopants on the blue phase (BP) range of the chiral nematic liquid crystal (N*LC) host were investigated. It was found that the bent-shaped dopants with branched terminal had better miscibility in LC host than the bent-shaped dopants with straight terminal, and contributed to induce BP and enhance the BP temperature range, with the maximum BP temperature range about 20.4°C. Besides, the electro-optical (E-O) performances of the blue phase liquid crystal doped with Th-BC6 (a bent-shaped dopant with the widest induced BP range in N*LC) were also explored. It was found that the drive voltage reduced first and then increased with the doping amount of Th-BC6 increasing. When the doping amount of Th-BC6 was about 15 wt%, the hysteresis could be strikingly reduced.

Blue phase liquid crystals affected by graphene oxide modified with aminoazobenzol group

ABSTRACTLiquid-crystalline blue phases (BPs) are stable only for very narrow temperature range between the isotropic and the chiral nematic phase that severely hinders their applicability. Herein, the aminoazobenzol group was chemically grafted onto epoxy group of graphene oxide (GO) via addition reaction. Successful grafting of aminoazobenzol group was confirmed using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), UV–vis absorption spectra and thermogravimetric analysis (TGA). The resultant aminoazobenzol group–modified GO sheets, which is reduced (RGO-Az), were easily redispersable in common organic solvents or liquid crystals (LCs). By doping different contents of RGO-Az, nanosheets could stabilise BP and increase the BP range. When doped with 0.5 wt% RGO-Az, the mixtures show the wider range with 5.9°C than the range with 3.6°C of BPLCs without RGO-Az. Meanwhile, the phase sequence and the range of the aforementioned phases are reproducible upon heating and cooling, which shows that the BPs doped with RGO-Az nanosheets are thermodynamically stable.

Wide blue phase range observed in simple binary mixture systems containing rodlike racemic biphenyl mesogens with 2-octyloxy tails

The widest temperature range of BP (∼34 K) can be induced by adding only 10 wt% chiral dopant ISO(6OBA)2 with high HTP into the rodlike racemic biphenyl compound C6OBiPhI-H.

Blue Phase Range Widening Induced by Laponite Nanoplatelets in the Chiral Liquid Crystal CE8

We report on the widening of blue phase range induced by surface-functionalised laponite nanoplatelets dispersed in a chiral liquid crystal. The results are obtained by means of high-resolution ac calorimetry and optical microscopy and they are reproducible upon heating and cooling, identifying thermodynamically stable blue phases. It is shown that nanoplatelets target mostly the cubic structure of blue phase I and increase its temperature stability range by a factor of two. The present results are in agreement with recent findings that anisotropic nanoparticles tend to effectively stabilise blue phase I.

Effect of the Addition of Mesogenic Thiol Ligand Modified Gold Nanoparticles on the Thermal Stabilization of Blue Phases

In this paper, we introduce surface modified gold nanoparticles with mesogenic thiol ligands in liquid crystal, for expansion of the temperature range of blue phases (BPs). We have used polarized optical microscope and UV-vis spectrophotometer to identify the thermal stabilization of BPs. The BPs range of nanoparticles doped liquid crystal is significantly dependent upon the addition amount of gold nanoparticles, and the molar ratios of attached ligands [4′-(10-mercaptodecyloxy)biphenyl-4-carbonitrile and dodecanethiol]. This study could provide a new and facile strategy to stabilize BPs, from the aspect of the surface modification of nanoparticles.

The effect of graphene on liquid-crystalline blue phases

The stabilization of liquid-crystalline blue phases is recently attracting considerable interest because of the envisioned applications in fast optical displays and tunable photonic crystals. We report on the effect of surface-functionalized graphene nanosheets on the blue phase range of a chiral liquid crystal. Calorimetric and optical measurements, reproducible on heating and cooling, demonstrate that the resulting soft nanocomposite exhibits an increased blue phase temperature stability range for a minute concentration of dispersed graphene. The impact is stronger on the ordered, cubic structured blue phase I. These findings suggest that anisotropic nanoparticles may be of great usefulness for stabilizing blue phases.

Effect of anisotropic MoS2nanoparticles on the blue phase range of a chiral liquid crystal

Liquid-crystalline blue phases are attracting significant interest due to their potential for applications related to tunable photonic crystals and fast optical displays. In this work a brief theoretical model is presented accounting for the impact of anisotropic nanoparticles on the blue phase stability region. This model is tested by means of high-resolution calorimetric and optical measurements of the effect of anisotropic, surface-functionalized MoS2 nanoparticles on the blue phase range of a chiral liquid crystal. The addition of these nanoparticles effectively increases the temperature range of blue phases and especially the cubic structure of blue phase I.

Effects of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles on the temperature range of liquid crystalline blue phases: a systematic study

Four series of symmetrically 2,5-disubstituted 1,3,4-oxadiazoles with different lateral substituents and terminal alkoxy chain length were synthesised and characterised. Then, all these bent-shaped compounds were separately doped into the blue phase (BP) liquid crystal host and their effects on the BP range of the host were investigated, which shows that the BP ranges varied greatly with the difference in the structure of 2,5-disubstituted 1,3,4-oxadiazoles and their doped concentration. Moreover, in order to explore the influence of the inherent molecular geometry and properties of the bent-shaped molecules on the stability of BPs, the molecular structures of all the compounds were studied by using the theory of density functional theory, and the optimised structural parameters of the molecules were calculated at the B3LYP/6–31G* level.