Liquid Crystal 5CB Research Articles

Molecular Dynamics, Dielectric Properties, and Textures of Protonated and Selectively Deuterated 4'-Pentyl-4-biphenylcarbonitrile Liquid Crystal.

Using liquid crystals in near-infrared applications suffers from effects related to processes like parasitic absorption and high sensitivity to UV-light exposure. One way of managing these disadvantages is to use deuterated systems. The combined 1H and 2H nuclear magnetic resonance relaxometry method (FFC NMR), dielectric spectroscopy (DS), optical microscopy (POM), and differential scanning calorimetry (DSC) approach was applied to investigate the influence of selective deuteration on the molecular dynamics, thermal properties, self-organization, and electric-field responsiveness to a 4'-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal. The NMR relaxation dispersion (NMRD) profiles were analyzed using theoretical models for the description of dynamics processes in different mesophases. Obtained optical textures of selectively deuterated 5CB showed the occurrence of the domain structure close to the I/N phase transition. The dielectric measurements showed a substantial difference in switching fields between fully protonated/deuterated 5CB and selectively deuterated molecules. The DSC thermograms showed a more complex phase transition sequence for partially deuterated 5CB with respect to fully protonated/deuterated molecules.

Electro-Optic Kerr Response in Optically Isotropic Liquid Crystal Phases

The results of an experimental investigation of the temperature and wavelength dependence of the Kerr constant (K) of mixtures with an increasing amount of chiral dopant in an isotropic liquid crystal phase are reported. The material was composed of a nematic liquid crystal (5CB) and a chiral dopant (CE2), which formed non-polymer-stabilized liquid crystalline blue phases with an exceptionally large value of K∼2 × 10−9 mV−2. The measurements were performed on liquid and blue phases at several concentrations covering a range of temperatures and using three wavelengths: 532 nm, 589 nm and 633 nm. The work focused on changes caused by concentration and their impact on the increase in the value of K, and it was found that in the case of the 5CB/CE2 mixture these changes were significant and quite systematic with temperature and wavelength. It is shown that the dispersion relation based on the single-band birefringence model described K well in isotropic liquid crystal phases at all of the measured concentrations. In an isotropic fluid, both temperature-dependent parameters in the dispersion relation had a simple linear form and, therefore, the K-surface could be described by only four constants. In the blue phase, the expression reproducing the temperature variation of K depended on concentration, which could vary from being almost linear to quasi-linear and could be represented well by an inverse exponential analytic expression.

Protein assay and immunoassay based on nematic thermotropic and lyotropic liquid crystals quantitated by haze measurement

Haze measurement is the cornerstone for assessing the transparency or opaqueness of liquid crystals (LCs) in applications such as smart windows and display technologies. In this study, we present a novel application of haze measurement as the quantitative approach for LC-based biosensing. Protein assay with bovine serum albumin (BSA) as the protein standard and immunoassay of the cancer biomarker CA125 were performed with the thermotropic LC 5CB and the nematic phase of the lyotropic chromonic LC sunset yellow. We observed that the brightness of LC optical texture increased with increasing analyte concentration due to enhanced light leakage caused by the attenuation of the vertical anchoring force of the surface alignment reagent coated on the glass surface. On the other hand, the haze value decreased as the amount of BSA or CA125 at the LC–glass interface increased, indicating that the scattering angle of the incident light was reduced. By calculating the percent difference in haze value, W (%), which gave rise to a positive correlation between the result of haze analysis and analyte concentration, a limit of detection (LOD) of 1.2 × 10−3 and 5.6 × 10−5 g/mL for BSA and CA125, respectively, was achieved by detection with 5CB, whereas the LOD values for BSA and CA125 were 1.0 × 10−12 and 1.9 × 10−9 g/mL, respectively, when detected with nematic sunset yellow. To the best of our knowledge, this study provides the first demonstration of the feasibility and simplicity of quantitative analysis by haze measurement in LC-based biosensing.

Improving the electro-optical properties of MoS2/rGO hybrid nanocomposites using liquid crystals

Hybrid systems of two-dimensional (2D) materials (such as graphene-family materials and 2D transition metal dichalcogenides) are attracting much attention due to their distinctive optoelectronic, thermal, mechanical, and chemical properties. The application perspectives of these materials in various fields further expand when enriching those with liquid crystals (LCs) primarily due to their enhanced tunability and functionality. In this study, we report on the hydrothermal synthesis of hybrid nanocomposites composed of MoS2 and rGO and discuss tuning possibilities of their electro-optical properties by incorporating thermotropic LCs. In particular, we demonstrate that the incorporation of 5CB LC increases the sensitivity and charge storage efficiency of the hybrid nanocomposites. In addition, we also present the responsivity, detectivity, and response time properties of the hybrid nanocomposites of MoS2/rGO, both with and without the inclusion of nematic LCs. Furthermore, we demonstrate that the system exhibits a 5CB-induced photocurrent switching effect. We believe the findings will open new doors for applications of these materials in optoelectronics and photonics.

Study of mesomorphic, thermal and optical properties of 4-pentylbenzoic acid (5BA) and 4-n-alkyl-4́-cyanobiphenyl (nCB; n = 5, 6) supramolecular hydrogen bonded mesogenic complexes

Within the scope of this study, the process of producing and analyzing a liquid crystalline substance (supramolecular hydrogen-bonded mesogen) is presented. The formation of this mesogen involves the use of two chemicals, namely 4-pentylbenzoic acid (5BA) and 4-n-alkyl-4́-cyanobiphenyl (nCB; n = 5, 6). Equimolar (1:1) 5BA/5CB and 5BA/6CB binary combination samples have been organized by using one at a time mixing 5CB and 6CB liquid crystal chemical substances with 5BA. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) are employed for the examination of phase transitions, and liquid crystalline phase texture properties of the produced mesogens. The phase transformation sequence that occurred during heating and cooling is Crystal (Cr) ↔ Smectic A (SmA) ↔ Nematic (N) ↔ Isotropic (I) with the 1st order or weakly 1st order transition. The nematic range value observed for 5BA/6CB is considerably smaller than the nematic range value observed for 5BA/5CB, but the thermal mesophase range value for both is approximately the same. Fourier-transform infrared (FTIR) evaluation of 5BA, 5CB, and their hydrogen-bonded combos (5BA/nCB; n = 5, 6) confirmed attribute peaks. The X-ray diffraction (XRD) study revealed that the produced mesogens possess a crystalline structure. In addition, UV–Vis experiments demonstrated that the increase in alkyl chain length in the combination resulted in a decrease in absorbance and wavelength values, while leading to an increase in absorbency and band gap energy values. These results propose workable purposes for the synthesized substances in liquid crystal displays and other optoelectronic devices. Overall, the findings display the feasibility and viability of these novel hydrogen-bonded liquid crystalline mesogens in various technological applications.

Influence of surfactants in nematic liquid crystal droplets

Liquid crystals in spherical droplets are highly sensitive to surfactants that control their orientation at interfaces. These molecules are widely used in optics. We fabricated 5CB liquid crystal droplets using SDS, CTAB, and DTAB surfactants at varying concentrations. We observed the transition from bipolar to radial at SDS concentration of 0.4 mM in 80 s, and from radial to bipolar at SDS concentration of 0.5 mM in 45 s. Surfactant concentration is the primary factor affecting liquid crystal droplet configuration, while headgroup, tail length, and architecture have minimal impact beyond the amount of absorbed surfactant in nematic liquid crystal droplets.

Microfluidic flow tuning via asymmetric flow of nematic liquid crystal under temperature gradient

In this work, efficient microfluidic flow rate tuning based on the asymmetric flow of nematic liquid crystal 5CB under a horizontal temperature gradient is studied. Rectangular microchannels with the width of 100 μm are fabricated through soft lithography and treated with homeotropic surface anchoring conditions. Polarized optical microscopy is applied to explore the unique optical anisotropic characteristics of the nematic liquid crystal. The asymmetric velocity profiles in the microchannel are obtained by particle tracking velocimetry. The effects of temperature, flow rate, and aspect ratio on the velocity profile and split ratio of the asymmetric flow are quantitatively studied for the first time, while the mechanism of the flow asymmetry of the nematic liquid crystal is discussed. The results show that the asymmetric flow of the nematic liquid crystal occurs after the horizontal temperature gradient is applied, with the velocity in the heated region markedly higher than its counterpart. The split ratio of the asymmetric flow increases with the increase in the temperature gradient and the decrease in the flow rate. The aspect ratio influences the asymmetric flow through approaches of average velocity and surface anchoring strength, while the former is more distinct. The impacts of temperature gradient, flow rate, and aspect ratio on the flow asymmetry of nematic liquid crystals are caused by the coupling between physical properties, velocity field, and director field. Microchannels based on the asymmetric flow characteristics of nematic liquid crystals can act as a novel kind of temperature-controlled microvalve to achieve efficient microfluidic flow tuning.

Influence of proteins on the dielectric characteristics of 5CB and 8CB liquid crystals

ABSTRACT In this paper, we study the influence of the protein Bovine Serum Albumin (BSA) on the dielectric properties of liquid crystals (LCs) such as 4-cyano-4-pentyl biphenyl (5CB) and Octyl-4-biphenylcarbonitrile (8CB). Studying the effect of proteins on the dielectric properties of LC is essential for both fundamental research and practical applications in material science, biomedical engineering, biotechnology, and optoelectronic devices. It helps understand the protein behaviour on the surface of LCs, which offers an opportunity to develop novel sensing platforms. A polarising optical microscope (POM) was used to examine the correlation between textures formed by LCs interacting with different concentrations of BSA. In the dielectric studies, dielectric parameters such as impedance (Z), real (Z’) and imaginary (Z’’) parts of the impedance, and the tangential loss (tan δ) were measured. The investigation involved analysing relaxation times using the collected data, revealing distinct behaviours between 5CB and 8CB liquid crystals. Bode and Nyquist’s plots were constructed and analysed to investigate the changes LCs undergo while interacting with BSA. An equivalent electrical circuit (EEC) was constructed using Bode and Nyquist data, from which circuit element values were successfully extracted. The results obtained from the POM studies and the interferences drawn from the EIS can help enhance the performance of protein-based liquid crystal devices.

An investigation of the effect of inducing molecular alignment on the lubrication performance of 5CB liquid crystal

The lubrication alignment behaviors of 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystal were investigated. A 60 s-long running-in pre-treatment was first performed using micro-sized diamonds. The ball was then deflected by a certain direction and an alignment agent (Sebacic Acid) was applied on the disc. Results show that the coefficients of friction for GCr15 and Si3N4 self-matching pairs were reduced to 0.036 and 0.017 respectively, 45.5 % and 67.3 % lower than the ones lubricated directly with 5CB. The surface morphology after running-in-deflection was smoother and flatter, with enhanced surface texture characteristics. It is believed that increased the order parameter of 5CB, induced by the synergistic effect of the alignment agent and running-in-deflection, is the reasons for the improvement in lubricating performance.

Proposed prototype for a quantitative biosensor for insulin detection using a liquid crystal

In this paper, we present a novel approach for label-free detection of human insulin using 5CB liquid crystal (LC). Monitoring insulin levels in the body is essential for treating diseases like diabetes, which are caused by insufficient production or inefficient use of insulin. Contemporary techniques of detection rely on glucose detection, and limited information is available on the direct detection of insulin. A simple method using a common room temperature LC 4-cyano-4-pentyl biphenyl (5CB) interacting with different concentrations of insulin, observed through a polarising optical microscope (POM), is reported in this paper. An analysis of observed textures revealed the detection of insulin as low as 25 μM concentration. The distinguishable features of the observed textures provide a scale for estimating insulin concentration. The effect of different pH and salt concentrations was studied in order to understand the optimal working condition of the proposed biosensor. Image J analysis demonstrated a positive correlation (R2 equal to 0.9553) between grey index (GI) values and human insulin concentrations. RGB analysis and interference studies confirmed the biosensor’s specificity in insulin detection. To correlate the textures to the happenings at the molecular level, docking studies were carried out. In addition to this, properties such as aromaticity, H-bond, hydrophobicity, interpolated charges, ionizability and solvent accessible area (SAS) in the minimum energy binding sites of 5CB-LC and human insulin chains were measured to know more about the interaction properties. This novel strategy shows promise for improving insulin detection sensitivity and accuracy, ultimately leading to better diabetes management and healthcare outcomes.

Exploring the electro-optical properties of nematic liquid crystal through incorporation of ZnCuGaS2 core/shell quantum dots

ABSTRACT The current study focuses on elucidating the interaction mechanisms between ZnCuGaS2 quantum dots (QDs) and nematic liquid crystals (NLCs) (5CB), intending to comprehend how this interaction leads to the alteration of electro-optical properties of the host material. Various concentrations of QDs were incorporated into NLCs and investigated to examine their emission and transmittance characteristics. Remarkably, an enhancement (~68%) in photoluminescence was observed for the concentration of 0.04 wt. %, adding an intriguing aspect to the findings. A notable decrease in the threshold voltage, from 1.5 V (in pure NLC) to 0.5 V, was observed for the optimised concentration (0.04 wt. %) calculated using transmittance-voltage measurement. This sample exhibited a noteworthy improvement in optical transmission, showing an increase by 2.7 times compared to pure NLC. Fundamentally, the introduction of QDs leads to a reduction in light leakage centres and ionic impurities, consequently enhancing radiative recombination. Moreover, the memory effect of the sample was evident in the capacitance-voltage data, revealing that the NLC with QDs significantly increased the capacitance value from 290 pF to 466 pF when compared to the pure NLC. The objective of the present research is to examine the impact of QDs on NLC concerning key parameters such as mentioned above.

5CB molecular dynamics on TiO2-coated planar aligned ITO electrodes

ABSTRACT 5CB liquid crystal (LC) is a well-studied material for a variety of applications due to its orientational ordering and viscosity. LCs mostly suffer from ionic impurities which can be filtered using metal oxide nanoparticles. Beyond this conventional role of TiO2 nanoparticles (NPs) in ionic impurity filtration in LCs, we have employed a new methodology to improve the planar orientation of 5CB molecules by depositing a thin layer of NPs on either side of the ITO electrode. The 5CB LC exhibits a typical birefringent schlieren texture; however, the presence of TiO2 layer alters the molecular orientation. On the TiO2 surface, the 5CB LC molecules showed schlieren defect points characterised by both twofold (s = ± 1/2) and fourfold (s = ± 1) brush-like structures. The change in texture and lowering of dielectric permittivity might be attributed to the change in the pretilt angle of 5CB molecules owing to the mutual interactions between 5CB and TiO2 layer. Remarkably, the 5CB LC within the TiO2-coated cell attains the isotropic phase at lower temperature as compared to the cells coated with polyimide SE-130. The underlying mechanism for coarsening kinetics in the 5CB is elucidated using the Lifshitz-Slyozov-Wagner (LSW) theory.

Preliminary study of the superlubricity behavior of ZrO2/PI lubricating with liquid crystal

This article has investigated the friction behavior of a tribological system composed of a liquid crystal and polyimide. In this tribological system, ZrO2 and PMDA-ODA polyimide film used as a friction pair, and the liquid crystals used as lubricants including the single liquid crystal 5CB and the mixed liquid crystals LCs1 (5CB-5CEPO2), LCs2 (5CB-3CEPC3), LCs3 (5CB-2CEPPN), and conducted friction coefficient comparison experiments with n-hexadecane. It was found that the average friction coefficient of the LCs3 (90% 5CB + 10% 2CEPPN) is the smallest at the load of 5 N and the velocity of 200 rpm, which is 0.00113. Load and velocity selection experiments were investigated of LCs3, as well as polyimide film’s surface analysis including scanning electron microscope, white-light interference, polarization microscope, and surface-enhanced Raman scattering spectra. The results of the surface analysis indicated that some groups in the main chain and branch chain of the polyimide molecules are oriented parallel to the polyimide surface after rubbing.

The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe3O4 with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications.

Enhanced liquid crystal performance through alkoxybenzoic acid doping

ABSTRACT This study investigates the impact of doping agents, 4-octyloxybenzoic acid (8OBA) and 4-octyloxy-3-fluoro benzoic acid (8OBAF), on the thermodynamic and electro-optical properties of the nematic liquid crystal 5CB. The differential scanning calorimetry, dielectric, and polarising optical microscopic measurements revealed intriguing properties. The doped liquid crystal samples exhibit higher phase transition temperatures, increasing birefringence, and order parameters. Dielectric measurements disclose reduced free ion concentration with 8OBA and increased concentration with 8OBAF in the liquid crystal matrix. The threshold voltage, switching time, and rotational viscosity were also diminished in the 5CB + 8OBA mixture, whereas these parameters were increased in the 5CB + 8OBAF mixture due to the strong intermolecular interaction with liquid crystals. The results presented here demonstrate that 8OBA dopant can be used to achieve high thermal stability of the nematic liquid crystal phase with fast response times and low threshold.

Using orientational transition of acetone-doped liquid crystal triggered by vanillin as a naked-eye vanillin sensor

Vanillin is an aromatic organic compound that is widely used in the food and cosmetics industries. The development of a simple and rapid method for the naked-eye detection of vanillin is essential for monitoring the vanillin production process. In this study, liquid crystal 5CB (4-cyano-4’-pentylbiphenyl) is doped with acetone and used as a sensing platform to detect vanillin in alkaline solutions with high specificity for the first time. Before the addition of vanillin, the acetone-doped 5CB adopts a homeotropic orientation and appears dark due to the formation of an electrical double layer (EDL) at the 5CB/water interface. In the presence of vanillin, it forms a complex with acetone inside 5CB, disrupting the EDL and the homeotropic orientation of 5CB. The event leads to a dark-to-bright transition which can be used to quantify the concentration of vanillin in a range between 0.1 and 25 mg/L. The limit of detection (LOD) for the vanillin sensor is 0.06 mg/L. As a proof of concept, the sensor is employed to monitor the vanillin concentration during oxidation of coniferyl alcohol. In the presence of 5000 mg/L of H2O2 and 1 mg/L iron tetraamidomacrocyclic ligand (Fe-TAML), 1750 mg/L of coniferyl alcohol can be converted to 393.0 mg/L of vanillin after a 30-min reaction at room temperature. This study demonstrates potential applications of the acetone-doped liquid crystal sensors for monitoring the production of vanillin under various conditions.

Improvement of rewriting time of optically driven liquid crystal display by azo-dye doping

ABSTRACT Optically driving liquid crystal display (ODLCD) uses polarized light field to control the orientation of the liquid crystal, and the display content can be maintained without external electric field, with extremely low power consumption. However, it has a long rewriting time, which is difficult to achieve industrialization. In order to improve the rewriting performance, the influence of the rotational viscosity of the mixed system of azo-dyes (SD1, MR) and nematic liquid crystal (5CB) on the rewriting speed is investigated. The experimental results show that the electro-optical properties of SD1-5CB and MR-5CB have great changes after irradiation by polarized light, among which the SD1-5CB is the best to improve the performance. With the increase of SD1 concentration, the rotational viscosity of SD1-5CB decreases significantly due to the change of cis-trans isomerization of azo-dye, and the optimal doping concentration is 0.5 wt%. In this case, the rewriting time is shortened from 45 s to 11 s, which has the potential to broaden the application of ODLCD.

An investigation of the effect of running-in with micron-sized diamonds on the lubrication performance of 5CB liquid crystal

The aim of this work was to examine the impact of running-in with micron-sized diamonds on the lubrication performance of 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystal (LC). It was observed that an appropriate running-in pretreatment resulted in a remarkable 37.9% decrease in the coefficient of friction (COF) compared to friction tests without running-in. This improvement in lubrication performance is believed to be attributed to the formation of a textured surface during the running-in process. Additionally, the study found a significant correlation between COF and various surface parameters, namely Sa, Ssk, Sku, Svk, and Spk. The wear surface exhibits characteristics such as high Sku, negative Ssk, Svk/Spk ratios, and smaller Str under the optimal running-in conditions.

Room-temperature ferroelectric nematic liquid crystal showing a large and diverging density.

The ferroelectric nematic phase (NF) is a recently discovered phase of matter in which the orientational order of the conventional nematic liquid crystal state is augmented with polar order. Atomistic simulations suggest that the polar NF phase would be denser than conventional nematics owing to contributions from polar order. Using an oscillating U-tube densitometer, we obtain detailed temperature-dependent density values for a selection of conventional liquid crystals with excellent agreement with earlier reports. Having demonstrated the validity of our method, we then record density as a function of temperature for M5, a novel room-temperature ferroelectric nematic material. We present the first experimental density data for a NF material as well as density data for a nematic that has not previously been reported. We find that the room-temperature NF material shows a large (>1.3 g cm-3) density at all temperatures studied, notably including phases without polar order. An increase in density at phase transitions is observed. The magnitude of the increase for the intermediate-to-ferroelectric nematic (NX-NF) transition is an order of magnitude smaller than the isotropic-nematic (I-N) transition. We then probe potential consequences that may result from an elevated density through measurement of the refractive indices (no and ne). The navg of M5 is compared with 5CB and polar smectic liquid crystals. We observe how the highly polar nature of the system counteracts the effects of an increase in density. With knowledge of experimental density, we are able to derive an approximation that yields the polar order parameter, 〈P1〉, from polarisation measurements. Present results may be typical of ferroelectric nematic materials, potentially guiding material development, and is especially relevant for informing ongoing studies into this emerging class of materials.

Hydrodynamic cavitation of nematic liquid crystal in Stokes flow behind bluff body with different shapes in microchannel

Hydrodynamic cavitation, which occurs when the local pressure is below the saturated vapor pressure in hydrodynamic flow, is ubiquitous in fluid dynamics and implicated in a myriad of industrial and biomedical applications. Although extensively studied in isotropic liquids, corresponding investigations in anisotropic liquids are largely lacking. In this paper, the hydrodynamic cavitation in the bluff body bypass flow of nematic liquid crystal 5CB in the microchannel is experimentally investigated. By 5CB, we mean the thermotropic liquid crystal 4′-pentyl-4-biphenylcarbonitrile. When the Reynolds number is in the range of 3 × 10−4 < Re < 1.2 × 10−3, a special flow phenomenon behind the bluff body is observed, namely, the disclination loop. The critical Reynolds number of cavitation inception varies with the shape of the bluff body, while the lowest value corresponds to the triangular bluff body. The hydrodynamic cavitation occurs in the Stokes flow regime with the Reynolds number significantly lower than 0.1 for all bluff bodies. There is a close relation between the oscillation behavior of cavitation domains and the structure of the bluff body. In addition, the pressure difference between the inlet and outlet of the microchannel shows linear relation with the Reynolds number rather than the quadratic relation for isotropic fluids, which proves the presence of shear thinning in the flow of nematic liquid crystals. The study in this paper on the hydrodynamic cavitation of nematic liquid crystal can broaden the research on providing new approaches for the enhancement of fluid mixing and heat transfer in microfluidic chips.