Liquid Crystal 5CB Research Articles

Real-time optical detection of mercury contamination in drinking water using an amphiphilic recognition probe at liquid crystal/aqueous interfaces.

Mercury contamination is a global environmental issue due to its toxicity and persistence in ecosystems. It poses a particular risk in aquatic systems, where it bioaccumulates and biomagnifies, leading to serious health impacts on humans. Therefore, effective detection technologies for mercuric ions in natural water resources are highly desirable. However, most existing detection methods are time-consuming, require complicated sample pre-treatment, and rely on expensive equipment, which hinders their widespread use in real-time detection. Here, we present a convenient, rapid, portable, user-friendly, and cost-effective sensing system for detecting Hg2+ ion contamination in water. This system utilizes a highly selective, amphiphilic, and structurally simple molecular probe, N-dodecylamine-di-thiocarbamate (DDC). DDC molecules align at the interface between the liquid crystal (LC) and water, inducing a homeotropic LC orientation. In water samples contaminated with Hg2+, a bright optical texture is observed, indicating the alignment of the 5CB LC in a planar manner at the LC/aqueous boundary. The minimum detectable concentration (LOD) for Hg2+ ions is 5.0 μM in distilled water, with a broad detection range from 5.0 μM to 2 mM. The sensor selectively detects Hg2+ ions over other common interfering metal ions, including Pb2+, Co2+, Ni2+, Cu2+, Cd2+, Zn2+, Cr2+, Mg2+, Na+, K+, and Ca2+. Boolean logic gates, bar graphs, and truth tables are employed to explain the selectivity of this liquid crystal-based sensor. This work demonstrates the significant potential of the sensor for monitoring mercuric ions in natural water resources, offering a promising strategy for controlling mercury pollution.

Experimental investigations of DGEBA epoxy resin dispersed liquid crystal polymer systems for the development of new electronic devices

The DGEBA: Diglycidyletherbisphenol A and Liquid Crystal (4′-Pentyl-4-Biphenylcarbonitrile (5CBLC)) have been used to fabricate the so-called DGEBA epoxy dispersed 5CB liquid crystals (DED5CBLC). The XRD study's findings suggest that 5CBLC fillers can be used to change the properties of DGEBA epoxy without significantly changing its structure. Results from optical measurements reveal that the amount of 5CBLC filler added to the new disc shape system can adjust the band gap. This provides a way to design disc shape systems with desired optical properties. A promising correlation exists between optical linear susceptibility, third nonlinear optical, and nonlinear refractive index with 5CBLC filler in the DGEBA epoxy matrix. This correlation is since all three of these properties are told to the electronic structure of the DGEBA epoxy matrix. AC-impedance and AC conductivity properties of DED5CBLC disc shape systems filled with various wt% CB molecules have been good for adding 5CBLC content and applied field frequency. The results show that the AC conductivity of the composite spreads with rising wt% 5CBLC filler content and frequency. The continuous Jonscher fitting theoretical curve can be used to characterize the relaxation process and predict the system's electrical properties at different frequencies. The shrink in impedance directs that the composite substance befalls more conductive.

Thermal and electric field effects on the nonlinear optical response of a cyanobiphenyl liquid crystal doped with carbon dots

The present study is devoted to the investigation of the nonlinear optical response of a cyanobiphenyl liquid crystal (8CB) doped with carbon dots derived from dansyl chloride (CD-DsCl). Using the time-resolved z-scan technique, it is investigated how the CD-DsCl addition affects the nonlinear refractive coefficient of planar liquid crystal samples. The temperature dependence of nonlinear optical responses of pristine and doped samples are analyzed close to smectic-A - nematic and nematic - isotropic phase transitions. Furthermore, the effects of an external electric field are analyzed. Our results show that doped 8CB samples may exhibit an enhanced nonlinear optical response, which depends on the strength of the external field.

Rheological Properties Study of Polymer Dispersed Liquid Crystals Doped by SiO2 Nanoparticles

The present report discusses the development of a novel nano-composite using a polymer dispersed liquid crystal (PDLC) and inorganic silicon dioxide (SiO2) nanoparticles. The aim of this work was to investigate the effect of the SiO2 nanoparticles on the rheological properties of the PDLC films. In our research described in this paper SiO2 nanoparticle-doped polymer dispersed liquid crystal films were made from a mixture of ethylene glycol phenyl ether methacrylate (EGPEMA) pre-polymer, 4-Cyano-4′-pentylbiphenyl (5CB) liquid crystals (LC) and SiO2 nanoparticles by the polymerization induced phase separation (PIPS) process. Doping the PDLC systems with SiO2 improved the rheological properties of these materials; the percolation (network formation) observed reflected the good interfacial adhesion between the nanoparticles, the polymer matrix and the LC. On the other hand, a decrease in the storage modulus (G′) and loss modulus (G″) of the PDLC systems after addition of the SiO2 nanoparticles confirmed their high flexibility and low crystallinity. A slight increase in G′ at 0.05 wt.% SiO2 resulted in the good mechanical strength of the doped PDLC. The viscoelastic behavior of the doped and undoped PDLC systems was confirmed at high frequencies. Thermal characterization by differential scanning calorimetry (DSC) showed a decrease in the glass transition temperature (Tg) of the PDLC with 0.05 wt.% of SiO2 nanoparticles, which showed that we had a more flexible material.

Effect of doping of organo-soluble carbon dots on ionic relaxation and conductivity of planar anchored cyanobiphenyl based nematic liquid crystal

We demonstrate here the striking effect of organo-soluble carbon dots (CDs, diameter ∼7- 8 nm) on the tunability of ionic relaxation and conductivity of the host, planar anchored thermotropic nematic liquid crystal (5CB, 4-Cyano-4′-pentylbiphenyl). The optical texture, frequency, temperature, and concentration dependent dielectric studies of pristine 5CB and CDs-5CB composites have been performed using the polarising optical microscope and high-resolution dielectric spectroscopy, respectively. The doping of 0.5 wt% CDs into planar anchored 5CB is resulted into the vertical alignment confirmed through the cross-polarised optical microscope. The doping of CDs in 5CB liquid crystal is resulted into an unprecedented faster ionic relaxation with an abatement of the ionic amplitude at room temperature. The shift in the relaxation frequency for 0.5 wt% CDs-5CB composite (induced vertical alignment) as compared to pristine 5CB (planar aligned) at 28 °C (nematic) is found to be ∼13 folds which is further increased to ∼18 folds at 38 °C (isotropic). A similar trend in the conductivity curve is also observed which further confirms the significant enhancement in conductivity value with increase in temperature and concentration of dopant CDs. The observation of enhanced ionic conductivity and faster ionic relaxation in CDs-5CB composites as compared to pristine 5CB are attributed to the complete change of planar to vertical alignment by doping of CDs on planar anchored liquid crystal sample cells. It appears that the plausible strong interaction between hydrocarbon chains of CDs and 5CB molecules through anchored substrate surfaces with increasing concentration of CDs and decrease in rotational viscosity of host 5CB with increasing temperature certainly plays a pivotal role in the tuning of ionic relaxation and conductivity in the liquid crystal sample cells. We certainly believe that our results would catalyze the cognizance of the ionic relaxation and conductivity in CDs-5CB composites and other related systems. Moreover, such composites with tunable ionic relaxation/conductivity would be certainly helpful in the fabrication of various tuneable devices such as wave front corrector, low frequency oscillation generators, dynamic light scattering, and so on.

Study on the effect of positive nematic liquid crystalline physical parameters on EHD properties

ABSTRACT The paper investigated the effects of viscous, elastic and dielectric parameters on the EHD performance of a positive nematic liquid crystal 5CB using CFD (CFD stands for Computational Fluid Dynamics) method. The governing equations including the continuity, momentum and angular momentum equation are presented. The constitutive equations for viscoelastic deformation and shear stress were established based on the L-E and O-F theories. The variables of micro-flow velocity, 5CB molecular director angular velocity, etc were chosen as the EHD (EHD is the abbreviation for electrohydrodynamic dynamics) feature quantities. The application of a DC electric field can cause continuous stable micro-flow in LC cell. The magnitude and direction of micro-flow are coupled with the angular velocity of the 5CB directors and are also influenced by viscoelastic parameters. The relaxation time is inversely proportional to the electric field intensity and dielectric parameters, proportional to the viscous parameters, and independent of the elastic parameters. Using the micro-PIV experiments, the numerical simulation results were tested. A stable approximate antisymmetric ‘S’ type flow profile was obtained in the 5CB cell which is in good agreement with the simulation result. The conclusions can lay a theoretical foundation for further study and application of liquid crystalline microfluidic driving methods.

Experimental studies on self-propulsion of deformable 5CB liquid crystal droplets in micellar solution

ABSTRACT The 5CB liquid crystal droplets were found to self-propel when suspended in a micellar solution of surfactant. We report experimental studies on the motion of these droplets in a quasi-two-dimensional geometry. The droplets exhibit directed, self-avoiding, or random coiling trajectories depending on the size of the droplets compared to the height of the sample cell. The flattened droplets showed smoother trajectories and with self-crossing. Interestingly, the large flattened droplets were found to exhibit deformation of their apparent cross-section during their self-propulsive motion. These unique properties of self-propulsion of 5CB liquid crystal droplets in surfactant solution can provide a new opportunity to study active biomimetic systems.

Extended centroid position method in liquid-crystal-based interrogation system for electric-field-modulated Fabry-Perot sensing

A polarized low-coherence interferometer (PLCI) based on a liquid crystal (LC) wedge is designed, and an associated demodulation method encompassing the tunability feature is proposed for tunable, standalone optical sensing. The application of an electric field to the LC material effectively decreases the birefringence value and the related dispersion relation, which in turn enhances the resolution of detection. The effect of the electric field on the demodulation of the cavity length is addressed by the successive determinations of the centroid positions of the PLCI interferograms. Through a comprehensive study of numerical simulations, the effectiveness of the proposed approach is explored relative to the conventional envelope detection methodology. In order to verify this method, an experiment with a Fabry-Perot-based fiber optic displacement sensor is carried out using a 5CB LC wedge-based PLCI setup in the presence of an electric field. The measurement accuracy of the cavity length is found to be 0.74% of full scale, rendering it more precise and robust than the conventional envelope detection method.

Study on the Memory Effect in Aerosil-Filled Nematic Liquid Crystal Doped with Magnetic Nanoparticles

A study on 5CB liquid crystal composites with SiO2 nanoparticles and an additional commixture with Fe3O4 nanoparticles using light transmission and SAW measurements is presented. The prepared liquid crystal composites exhibited an interesting memory effect characterized by the hysteresis of both light transmission and SAW attenuation responses investigated in the nematic phase. While in the case of SiO2 nanoparticles as dopants, the liquid crystal composite showed an improvement in the memory effect, the addition of Fe3O4 magnetic nanoparticles resulted in the memory effect decreasing. Additional studies showed a significant shift in both the threshold voltage and nematic–isotropic transition temperature. Measurements in the magnetic field confirmed the increasing memory effect according to that of pure 5CB. The properties of these composites could lead to a potential application for the fabrication of memory devices suitable for information storage.

A label-free 5CB-based aptasensor for highly selective optical detection of amoxicillin residue in freshwater samples

ABSTRACT A novel application of thermotropic liquid crystal (LC) 5CB in an optical aptasensor for the sensitive detection of amoxycillin (AMOX) antibiotic has been reported. In the studied system, the glass substrates were treated with dimethyloctadecyl [3–(trimethoxysilyl) propyl] ammonium chloride (DMOAP) and an aqueous solution of cationic surfactant cetyltrimethylammonium bromide (CTAB) was used to obtain a homeotropically aligned 5CB monolayer at the LC-aqueous interface resulting in a uniformly dark appearance. A highly specific amoxycillin aptamer (AMXA) was immobilised on the glass substrate as a target recognition probe for AMOX molecules. The specific binding of AMXA and AMOX molecules induces orientational changes in LC ordering resulting in a change in LC optical textures observed under a Polarized Optical Microscope (POM). A low limit of detection (LOD) of 10 nM for AMOX was obtained using this sensing system. Additionally, a high specificity for AMOX was also observed during comparative analysis. Finally, the developed biosensor was used to successfully detect AMOX in environments of potential application like tap water and lake water samples. Thus, the developed LC-based aptasensor can be a simple, sensitive and label‐free platform for monitoring real‐time levels of AMOX in freshwater environments.

Design of 5CB liquid crystal antenna for tunable microwave frequency applications

ABSTRACT Cyanobiphenyls (CBs) are a class of molecules with unique properties that make them highly versatile in various fields. Their anisotropic nature, low viscosity, and sensitivity to external stimuli make them ideal for applications in display technology, photonic devices, sensors, and in tunable antennas. In this article, we present the design and simulation of a 5CB LC antenna for tunable microwave frequency applications due to its fast response time and low dielectric loss than other CB materials. The proposed antenna contains two glass substrates with an air gap of 0.004 mm between them. The lower glass contains a size of 20 × 15 mm2, while the upper glass contains a size of 13 × 15 mm2. The proposed antenna produces two bands when there is an air gap between the glass plates; three bands when diodes are used for the radiating patch; and four bands when 5CB LC material is introduced between the glass plates as a dielectric medium. The same structure produces various frequency bands, which is a notable advantage compared to the existing state of the art. All the results shown in this manuscript were simulated and measured with the body of data available from the literature.

Alignment of Nematic Liquid Crystal 5CB Using Graphene Oxide

In this article, we employed the saturation voltage method (SVM) to investigate the interaction between a nematic liquid crystal (NLC) and a graphene oxide (GO) substrate. The SVM approach involved applying a potential difference (ΔV) to the cell containing the NLC (specifically, 5CB) to reorient the nematic director (n) from a parallel to a perpendicular configuration with respect to the cell’s surface. By utilizing sandwich cells with indium–tin oxide semi-transparent electrodes covered by GO, we measured the anchoring energy between the NLC and the thin GO film. To evaluate the strength of this anchoring energy, we compared the results with two other cells: one exhibiting strong anchoring energy (polyimide cell) and the other demonstrating weak anchoring energy (formvar cell). The influence of GO thin films on the alignment of nematic 5CB was distinctly observed.

Asymmetric Synthesis of Tetraphenylethylene Helicates and Their Full-Color CPL Emission with High glum and High Fluorescence Quantum Yield.

Tetraphenylethylene (TPE) helicates with single helical handedness not only owe high fluorescence quantum yield but also possess good helical chirality, showing an excellent circularly polarized luminescence active material. In this work, a new method for directly obtaining single-handed TPE helicates has been developed. By using chiral p-phenylenediamine derivatives as an intramolecular cyclization reagent of TPE, the single-handed propeller-like conformation and stable helical chirality of the TPE unit were obtained, avoiding complicated and expensive HPLC chiral column separation. The as-prepared chiral TPE helicates displayed strong emission with an almost quantitative fluorescence quantum yield (Φf) and strong circularly polarized luminescence (CPL). In addition, the chirality and CPL signals of the TPE helicates could be significantly magnified by the helical arrangement together with 4'-pentyl-4-biphenylcarbonitrile (5CB) liquid crystal molecules. Moreover, full-color CPL emissions with both a high absolute CPL dissymmetrical factor up to 0.43 and high Φf were afforded.

Effect of quantum dots on the phase behavior and order of 8CB liquid crystal

We experimentally investigate the impact of surface functionalized hydrophobic core-shell CdSe/ZnS quantum dots on the phase behavior and order of the host liquid crystal compound 4-cyano-4'-octylbiphenyl (8CB) by means of polarized optical microscopy, polarized micro-Raman spectroscopy and X-ray diffraction. The orientational order of the nanocomposite system is probed by means of birefringence measurements as a function of temperature and mass fraction of the quantum dots. The dispersion quality of the dopant in the samples, partial-aggregation phenomena and/or nanoparticle organization give rise to non-monotonic variation of the probed thermodynamic quantities. A critical dopant mass fraction above which the nematic phase becomes paranematic is evidenced. A phenomenological model accounts for phase separation effects and a qualitative interpretation of the experimental results. The impact of nanoparticles on the macroscopic nematic order is discussed in the frame of a random anisotropy Lebwohl-Lasher model.

Calibration-free method to study temperature dependence of microwave dielectric properties of nematic liquid crystals

ABSTRACTThe present article shows an original transmission-reflection-based method to characterise the microwave dielectric properties of liquid crystals. This new method offering broadband capabilities of transmission-reflection method without the need for vector network analyser calibration. It is based on two measurements in the frequency range: one measurement is performed with the empty cell, the other with the cell filled with the material. The analysis of the two recorded scattering matrices allows to eliminate all error terms and to extract real and imaginary parts of the complex dielectric constant. In this paper, we first present this method, its validation in comparison to other characterisation methods. Secondly, we present an appropriate measuring cell which allows measurements in the frequency range 26 GHz-40 GHz which is also well-suited for temperature-dependent measurements. This method is used to perform dielectric microwave measurements on 5CB liquid crystal. Finally, we discuss the temperature-dependent microwave dielectric properties (permittivity, losses and dielectric anisotropy).

English

This paper reports details of phase transitions of a new generation “Tertiary Liquid Crystal System” (TLCS). This TLCS was made with a mixture of 5CB, 6CB, and 7CB liquid crystals. The TLCS was run in DSC to find changes taking place in its heat flow as a function of time and temperature analyzed with Logger Pro. The sample of TLCS was run from -40 °C to 80 °C with a 20 °C/min ramp rate in DSC. It was observed that the TLCS shows two phase transitions on heating and one transition on cooling. All these transitions were found to shift when compared to their single members. The unique behavior of TLCS is that it never shows crystallization in cooling, even though the sample was cooled to -40 °C. This indicated an increase in its Nematic range, making it more useful in the Liquid Crystal Display (LCD) field.

Enhancement of electro-optical properties and phase transition temperature of thermotropic liquid crystal 5CB by doping with 4-n-pentylbenzoic acid

ABSTRACT Liquid crystalline materials that have been used in the display industry need to have a wide temperature-range nematic phase while remaining functioning in different climate conditions. In this work, a new binary mixture of thermotropic liquid crystal materials, particularly the nematic phase, has been studied. A widely used material 5CB (4-Cyano-4’−pentyl biphenyl), exhibiting nematics phase, and PA (4-Phenylbenzoic acid) were preferred. Mixtures of different concentrations of 5CB-PA were prepared and investigated using dielectric spectroscopy, phase transition and electro-optical responses techniques. It was found that not only was an improvement to the dielectric anisotropic achieved but also the nematic temperature range extended from 35 ºC to just above 50°C by adding 10 wt.%. On the other hand, the threshold voltage is increased by 10% for the same sample. In addition, elastic constants and response time showed similar behaviours upon increasing the loading concentration of PA, whereas the visco-elastic coefficient significantly declined. All the estimated values for the pure 5CB are in good agreement with the literature. This improvement in the operating temperature range is unique and suggests that the doping can lead to cheap and mass production of a stable liquid crystalline material for their application in the display industry.

Effect of Polymer Hydrophobicity in the Performance of Hybrid Gel Gas Sensors for E-Noses.

Relative humidity (RH) is a common interferent in chemical gas sensors, influencing their baselines and sensitivity, which can limit the performance of e-nose systems. Tuning the composition of the sensing materials is a possible strategy to control the impact of RH in gas sensors. Hybrid gel materials used as gas sensors contain self-assembled droplets of ionic liquid and liquid crystal molecules encapsulated in a polymeric matrix. In this work, we assessed the effect of the matrix hydrophobic properties in the performance of hybrid gel materials for VOC sensing in humid conditions (50% RH). We used two different polymers, the hydrophobic PDMS and the hydrophilic bovine gelatin, as polymeric matrices in hybrid gel materials containing imidazolium-based ionic liquids, [BMIM][Cl] and [BMIM][DCA], and the thermotropic liquid crystal 5CB. Better accuracy of VOC prediction is obtained for the hybrid gels composed of a PDMS matrix combined with the [BMIM][Cl] ionic liquid, and the use of this hydrophobic matrix reduces the effect of humidity on the sensing performance when compared to the gelatin counterpart. VOCs interact with all the moieties of the hybrid gel multicomponent system; thus, VOC correct classification depends not only on the polymeric matrix used, but also on the IL selected, which seems to be key to achieve VOCs discrimination at 50% RH. Thus, hybrid gels' tunable formulation offers the potential for designing complementary sensors for e-nose systems operable under different RH conditions.

Photo-Induced Relief in Rheology of Liquid Crystals

In this paper, we report the first experimental results on capillary shear flows of a nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl), arising due to interaction of the anisotropic liquid, correspondent to the continuous rotational symmetry, with photo-profiled polymer surfaces. The regular surface relief was obtained due to opto-mechanical deformation of azobenzene containing potoresponsive polymer film (PAZO) during irradiation with two-beam interference. Such surface treatment makes it possible to obtain a regular submicron profile with well-defined characteristics (direction, period, and height). The polarizing microscopy (PM) and dynamic light scattering (DLS) techniques were used to determine the direction of the surface orientation of LC and anchoring strength, which characterize the interaction of LC with the photo-profiled polymer surface. Two types of shear flows—spreading of LC droplets and capillary flow in a plane capillary, induced by the interaction of LC with one or two photo-profiled surfaces—were investigated for different directions of the flow relative to the direction of the relief. Strong anisotropy in the dynamics of the precursor film and contact line motion, as well as in the dynamical contact angle, was established. The experimental results were analyzed and compared with those previously obtained at the investigation of the spreading of LC droplets over a mechanically stamped submicron profile and capillary flows in plane capillaries with photo-aligned surfaces.

High-resolution dielectric anisotropy investigation of carbon nanotube-smectic-A liquid crystal dispersions: An upper limit of the latent heat and the pretransitional anomaly at the nematic-smectic-A transition.

Within the entire mesomorphic range, high-precision dielectric anisotropy data with the high-temperature resolution is presented for a highly polar smectic-A liquid crystal 8CB (octylcyanobiphenyl) as well as 8CB nanocomposites doped with both pristine multi-walled carbon nanotubes (p-MWCNTs) and carboxyl group (-COOH) functionalized MWCNTs (f-MWCNTs). The temperature variation of the nematic order parameter across both the nematic-isotropic (N-I) and the nematic-smectic-A (N-Sm-A) phase transitions of the neat 8CB and 8CB+MWCNT nanocomposites has then been derived from the dielectric anisotropy data within the framework of the Maier-Meier theory. With the inclusion of MWCNTs, both the N-I and the N-Sm-A transition temperatures have been noted to shift to lower temperatures as compared to the 8CB host. Also, for all 8CB+MWCNT nanocomposites, regardless of the surface functionalization, it has been well documented that the N-I transition is weakly first order, whereas the N-Sm-A transition remains continuous within the experimental resolution. For all investigated samples, the temperature dependence of the nematic order parameter has been shown to be quasitricritical, within the experimental resolution. From the attentive inspection of the dielectric anisotropy data in the vicinity of the N-Sm-A transition, the upper limits for a possible latent heat ΔH_{NA} for the 8CB host and all 8CB+MWCNT composites, for the first time, have been derived. The so-derived ΔH_{NA} values for all investigated samples have also been compared with those extracted from the optical birefringence data, and an excellent consistency has then been noted. The N-Sm-A pretransitional anomaly has been investigated and the effective specific heat capacity exponent α values have been yielded from the power-law analysis of our high-resolution Δɛ(T) data across the N-Sm-A transition for all investigated samples. It has been well documented that the incorporation of MWCNTs to the 8CB host leaves the N-Sm-A transition essentially bulklike. We discussed that, to some extent, the compliance of MWCNTs does not drive the N-Sm-A transition to 3D-XY-like behavior, that is the strength of de Gennes coupling will remain the same for all nanocomposites. This issue can be ascribed to the weaker nature of MWCNT disorder. In this work, for the first time, high-resolution Δɛ(T) data has been shown to be very adequate and offer an easy way to investigate the N-Sm-A transition as compared to calorimetric methods.