Liquid Crystal Nanoparticles Research Articles

Mechanochemical nanoparticle functionalization for liquid crystal nanocomposites based on COOH-pyridine heterosynthons

Nanoparticle/liquid crystal (NP/LC) composites can be stabilized by hydrogen bonding, a relatively strong, yet reversible interaction allowing for the annealing of defects.

Ferromagnetic nanoparticles in a ferroelectric liquid crystal: Properties of stable colloids in homogeneous cells

Stable colloids in ferroelectric liquid crystal (FLC) of fine ferromagnetic CoFe2O4 nanoparticles (NPs) coated with specially designed promesogenic ligands were obtained. The studying of FLC properties for these nanocomposite materials revealed significant changes in dielectric spectra and increase in rotational viscosity of FLC accompanied with noticeable degradation of texture. The changes in dielectric parameters have a pronounced NPs concentration dependence although it was shown that the cell surface contribute to these changes significantly, thus, the role of NPs in changing of the properties was critically revised. Monitoring of dielectric properties and other physical parameters of FLC with time confirmed a high stability of the material upon storage. The influence of magnetic field on basic parameters of FLC in NPs-FLC colloids was examined and explained taking into account highly developed and strongly interacting with LCs organic shell on the NPs surface. Despite a high stability and homogeneity of the composites, in magnetic field the materials do not reveal any significant changes from properties of pure FLC except of increase in viscosity which as a result of alignment of magnetic NPs along with magnetic field and strong interpenetration of LC molecules and NPs ligands.

Front Cover: Chiral Amplification by L‐Cysteine‐Capped Gold Nanoparticles in Lyotropic Chromonic Liquid Crystals (ChemNanoMat 12/2017)

Front Cover: Chiral Amplification by <i>L‐</i>Cysteine‐Capped Gold Nanoparticles in Lyotropic Chromonic Liquid Crystals (ChemNanoMat 12/2017)

Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal

ABSTRACTThe present work concerns with the investigation of the effect of dispersion of Silica (SiO2) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO2 NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO2 NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation Ps and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions.

Ferroelectric Nanoparticles in Liquid Crystals: Recent Progress and Current Challenges.

The dispersion of ferroelectric nanomaterials in liquid crystals has recently emerged as a promising way for the design of advanced and tunable electro-optical materials. The goal of this paper is a broad overview of the current technology, basic physical properties, and applications of ferroelectric nanoparticle/liquid crystal colloids. By compiling a great variety of experimental data and discussing it in the framework of existing theoretical models, both scientific and technological challenges of this rapidly developing field of liquid crystal nanoscience are identified. They can be broadly categorized into the following groups: (i) the control of the size, shape, and the ferroelectricity of nanoparticles; (ii) the production of a stable and aggregate-free dispersion of relatively small (~10 nm) ferroelectric nanoparticles in liquid crystals; (iii) the selection of liquid crystal materials the most suitable for the dispersion of nanoparticles; (iv) the choice of appropriate experimental procedures and control measurements to characterize liquid crystals doped with ferroelectric nanoparticles; and (v) the development and/or modification of theoretical and computational models to account for the complexity of the system under study. Possible ways to overcome the identified challenges along with future research directions are also discussed.

Chiral Amplification by L‐Cysteine‐Capped Gold Nanoparticles in Lyotropic Chromonic Liquid Crystals

AbstractTransfer of chirality from an adsorbed molecule to a metal nanoparticle surface, and from the resulting chiral nanoparticle to its surroundings, depends on numerous factors – structure of the adsorbed molecule, its size and shape, and its interactions with its specific environment – but is often difficult to understand and even more difficult to measure, visualize, and quantify. This severely limits the potential of chiral nanoparticles in a range of emerging applications as optical metamaterials, enantioselective catalysts, or chiral discriminators for biomacromolecules. We examine if chirality at the nanoscale (i. e. in gold nanoparticles capped with chiral ligand molecules) is uniquely able to generate more intense responses than their organic chiral counterparts in soft condensed matter utilizing lyotropic chromonic liquid crystals (LCLCs) forming the nematic phase. As a powerful manifestation of nanoscale chiral amplification, we show that L‐cysteine capped gold nanoparticles induce a tighter chiral twist within, and similar among, stacks of nematic LCLCs with several orders of magnitude fewer chiral L‐cysteine ligands in comparison to the free molecular L‐amino acid.

Dielectric and polarization switching studies in nickel nanoparticles dispersed ferroelectric liquid crystal mixtures

ABSTRACTWe have investigated the effect of nickel nanoparticles (NiNPs) in a pure ferroelectric liquid crystal (FLC) mixture. Dielectric spectroscopy was done in the frequency range of 20 Hz–10 MHz. Switching time, spontaneous polarisation, rotational viscosity has been measured using field reversal technique in SmC* phase. The spontaneous polarisation increases for NiNPs-FLC sample which may be due to the induced dipole moments around FLC molecules. Response time decreases with temperature and NiNPs dispersion. The relaxation frequency and dielectric strength of observed mode in SmC* phase is also discussed in pure FLC and NiNPs-FLC samples. The relaxation frequency in NiNPs-FLC sample decreases than pure FLC sample and found ∼120 Hz.

Placental-homing peptides attached to liquid crystal nanoparticles for selective targeting of the placenta

Several conditions are associated with increased preeclampsia (PE) risk. Whether altered maternal angiogenic factor levels contribute to risk in these conditions is unknown. Our objective was to compare angiogenic biomarker patterns in high-risk pregnancies and low-risk controls.We conducted a planned secondary analysis of a 2-center observational study of angiogenic biomarkers in high-risk women. A total of 156 pregnant women with a PE risk factor and 59 low-risk controls were studied. Serial maternal serum samples were collected during 3 gestational windows: 23-27 weeks, 28-31 weeks, and 32-35 weeks. Soluble fms-like tyrosine kinase 1 (sFlt1), soluble endoglin (sEng), and placental growth factor (PlGF) were measured by enzyme-linked immunosorbent assay. Geometric mean angiogenic biomarker levels and angiogenic ratio (sFlt1 + sEng):PlGF were compared with low-risk controls for each risk group, at each gestational window.Gestational biomarker patterns differed in PE risk groups as compared with low-risk controls. Women with multiple gestations had markedly higher sFlt1 and sEng at all gestational windows. Women with prior PE had higher sFlt1 and angiogenic ratio, and lower PlGF, from 28 weeks onward. Women with chronic hypertension had significantly higher angiogenic ratio for all 3 gestational windows, but differences disappeared when women with PE were excluded. Obese and nulliparous women had significantly lower PlGF, but no differences in the angiogenic ratio.High-risk groups have altered angiogenic biomarker patterns compared with controls, suggesting that altered production or metabolism of these factors may contribute to PE risk, particularly in women with multiple gestations and prior PE.

Effect of magnetic nanoparticles on the nematic-smectic-A phase transition

Recent experiments on mixed liquid crystals have highlighted the hugely significant role of ferromagnetic nanoparticle impurities in defining the nematic-smectic-A phase transition point. Structured around a Flory-Huggins free energy of isotropic mixing and Landau-de Gennes free energy, this article presents a phenomenological mean-field model that quantifies the role of such impurities in analyzing thermodynamic phases, in a mixture of thermotropic smectic liquid crystal and ferromagnetic nanoparticles. First we discuss the impact of ferromagnetic nanoparticles on the isotropic-ferronematic and ferronematic-ferrosmectic phase transitions and their transition temperatures. This is followed by plotting and discussing various topologies in the phase diagrams. Our model results indicate that there exists a critical concentration of nanoparticle impurities for which the second order N-SmA transition becomes first order at a tricritical point. Calculations based on this model show remarkable agreement with experiment.

Textural and optical studies of magneto-mesogen material for display applications

ABSTRACTIn this work, a magneto-mesogen material has been prepared by nematic liquid crystal (6OCB) and magnetic nanoparticles (Fe). The effect of small amount of Fe doping on textural behaviour and optical responses has been investigated in a planar aligned cell in the nematic phase. The doped sample shows relatively higher transmission intensity than pure 6OCB and decreases a threshold voltage from 1.4 V to 1.0 V. The UV-Vis spectra show that after dispersion the absorbance peak shift from 319 nm to 315 nm. The measured band gap in 6OCB and Fe-6OCB composite was found 3.71 eV and 3.72 eV respectively.

Twist-grain boundary phase induced by Au nanoparticles in a chiral liquid crystal host

ABSTRACTWe report on the stabilisation of the liquid-crystalline, twist-grain boundary A (TGBA) phase in mixtures of a chiral liquid crystal and surface-functionalised spherical Au nanoparticles (NPs) of 10 nm diameter. The results, obtained by calorimetric, optical, small-angle X-ray and plasmon resonance measurements, demonstrate that a TGBA phase, which is metastable for the pure liquid crystal host, can be effectively stabilised for a 3 K range in the presence of NPs. Moreover, the role of NPs size on the TGBA stabilisation is briefly discussed.

The effects of magnetic nanoparticles on oscillating behavior of a nematic liquid crystal cell

ABSTRACTMagnetic suspensions in anisotropic host fluids such as liquid crystals show interesting behavior that have attracted vast interest in many areas of science, technology, and medicine. Recently, suspensions of monodomain magnetic nanoparticles in nematic liquid crystals, called ferronematics, are extensively used in different technological applications. Dynamical ordering behavior in these magnetic materials is a complex subject due to several dynamic cross-couplings. In this work, the effects of magnetic nanoparticle dopants on the dynamical behavior of a nematic liquid crystal cell are discovered through studying the motion of a torsional oscillator in which the cell is contained. Dynamical features of the cell are investigated within the framework of continuum theory. The hydrodynamic equations of the ferronematic liquid crystal are calculated in the presence of an applied magnetic field. The velocity components and the displacement dependence of the velocity field in the cell are obtained. Then, the toque exerted on the cell contained in torsional oscillator is determined. This study is based on Leslie–Ericksen theory. The analysis is also used to study the resonant frequency as a function of the applied field. In this way, the key roles of the entropy of ferroparticle solution and anchoring induced ferronematic interactions become evident.

Molecular simulations of entangled defect structures around nanoparticles in nematic liquid crystals

ABSTRACTWe investigate the defect structures forming around two nanoparticles in a Gay–Berne nematic liquid crystal using molecular simulations. For small separations, disclinations entangle both particles forming the figure of eight, the figure of omega and the figure of theta. These defect structures are similar in shape and occur with a comparable frequency to micron-sized particles studied in experiments. The simulations reveal fast transitions from one defect structure to another suggesting that particles of nanometre size cannot be bound together effectively. We identify the ‘three-ring’ structure observed in previous molecular simulations as a superposition of the different entangled and non-entangled states over time and conclude that it is not itself a stable defect structure.

Targeted Plasma Membrane Delivery of a Hydrophobic Cargo Encapsulated in a Liquid Crystal Nanoparticle Carrier

The controlled delivery of drug/imaging agents to cells is critical for the development of therapeutics and for the study of cellular signaling processes. Recently, nanoparticles (NPs) have shown significant promise in the development of such delivery systems. Here, a liquid crystal NP (LCNP)-based delivery system has been employed for the controlled delivery of a water-insoluble dye, 3,3′-dioctadecyloxacarbocyanine perchlorate (DiO), from within the NP core to the hydrophobic region of a plasma membrane bilayer. During the synthesis of the NPs, the dye was efficiently incorporated into the hydrophobic LCNP core, as confirmed by multiple spectroscopic analyses. Conjugation of a PEGylated cholesterol derivative to the NP surface (DiO-LCNP-PEG-Chol) enabled the binding of the dye-loaded NPs to the plasma membrane in HEK 293T/17 cells. Time-resolved laser scanning confocal microscopy and Förster resonance energy transfer (FRET) imaging confirmed the passive efflux of DiO from the LCNP core and its insertion into the plasma membrane bilayer. Finally, the delivery of DiO as a LCNP-PEG-Chol attenuated the cytotoxicity of DiO; the NP form of DiO exhibited ~30-40% less toxicity compared to DiOfree delivered from bulk solution. This approach demonstrates the utility of the LCNP platform as an efficient modality for the membrane-specific delivery and modulation of hydrophobic molecular cargos.

Targeted Plasma Membrane Delivery of a Hydrophobic Cargo Encapsulated in a Liquid Crystal Nanoparticle Carrier.

The controlled delivery of drug/imaging agents to cells is critical for the development of therapeutics and for the study of cellular signaling processes. Recently, nanoparticles (NPs) have shown significant promise in the development of such delivery systems. Here, a liquid crystal NP (LCNP)-based delivery system has been employed for the controlled delivery of a water-insoluble dye, 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO), from within the NP core to the hydrophobic region of a plasma membrane bilayer. During the synthesis of the NPs, the dye was efficiently incorporated into the hydrophobic LCNP core, as confirmed by multiple spectroscopic analyses. Conjugation of a PEGylated cholesterol derivative to the NP surface (DiO-LCNP-PEG-Chol) enabled the binding of the dye-loaded NPs to the plasma membrane in HEK 293T/17 cells. Time-resolved laser scanning confocal microscopy and Förster resonance energy transfer (FRET) imaging confirmed the passive efflux of DiO from the LCNP core and its insertion into the plasma membrane bilayer. Finally, the delivery of DiO as a LCNP-PEG-Chol attenuated the cytotoxicity of DiO; the NP form of DiO exhibited ~30-40% less toxicity compared to DiOfree delivered from bulk solution. This approach demonstrates the utility of the LCNP platform as an efficient modality for the membrane-specific delivery and modulation of hydrophobic molecular cargos.

Random lasers tuning by combining a dye-doped liquid crystal and CdS nanoparticles

We report the development of LC (negative liquid crystal and mixing liquid crystals) random lasers doped with a gain medium and CdS nanoparticles. By performing frequency doubled 532nm Nd:YAG (yttrium aluminum garnet) laser as a function of excitation wavelength, we demonstrate laser action in a new category of materials, namely dye doped liquid crystal with semiconductor nanoparticles. The CdS nanoparticles prove to be perfect candidates for building, as shown, a series of laser systems. Lasing is presented in cells, freely suspended liquid crystal films. The optical emission properties are investigated in terms of spectral analysis, below and above lasing energy threshold behavior, emission efficiency, far field spatial laser modes intensity profiling, etc. As demonstrated, these DDLC random lasers with the CdS nanoparticles are very promising platforms for investigating the optical mechanism of cadmium sulfide.

Ordering of ferromagnetic nanoparticles in nematic liquid crystals.

Dispersions of magnetic nanoparticles in a nematic liquid crystal were investigated as magnetic fields were applied in three different boundary condition geometries: (i) planar substrates and B⊥n, (ii) planar substrates and B‖n, and (iii) homeotropic substrates and B⊥n. Particle chaining is observed when a magnetic field is applied, with a periodicity perpendicular to the chains. Furthermore, linear chains are observed for the magnetic field applied perpendicular to the director, while zigzag chains are formed when the magnetic field direction is parallel to the director field. This is attributed to a change from a dipolar defect configuration around dispersed nanoparticles, to a quadrupolar one, i.e. the change from satellite to Saturn-ring defects. This effect is largely independent of the sample thickness. The dynamic development of the chain length, as well as their two-dimensional order parameter was studied in all cases. Chain lengths increased rapidly until saturation at approximately l = 30 μm after a time of about t = 10 s. Similarly, the chain order parameters increased until saturation between S = 0.8-0.9, independent of sample geometry.

Structuralization of magnetic nanoparticles in 5CB liquid crystals.

This work is devoted to the study of highly stable composite systems of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB) doped with CoFe2O4 magnetic nanoparticles. Ferronematic samples were prepared with two different weight concentrations: sample A 0.085 wt% and sample B 0.062 wt%. The interaction of CoFe2O4 nanoparticles with the liquid crystal was investigated by small-angle X-ray-scattering and magnetization measurements. The obtained results reveal aggregates formed by magnetic nanoparticles that are oriented in the nematic phase. Moreover, the prepared samples show unexpected behaviour of a sudden change in magnetization, which is unusual for such ferronematics.

Effective and Facile Determination of Vitamin B6 in Human Serum with CuO Nanoparticles/Ionic Liquid Crystal Carbon Based Sensor

New insights in fabrication of a sensitive, carbon nanotubes-based electrochemical sensor for determination of vitamin B6 (PY) are presented in this work. This was achieved by exploring the interesting properties of a conductive composite based on manual casting of successive layers of carbon nanotubes mixed with ionic liquid crystal and CuO nanoparticles (GC/(ILC-CNTs)/CuO) over glassy electrode surface. The proposed sensor was successfully used for the simultaneous determination of binary mixtures of PY and other vitamins (B2, B9, B12 or C) with good resolution. Under optimized conditions, a linear calibration curve was obtained for the determination of vitamin B6 in blood serum within the range 0.5 μmol L−1 to 50 μmol L−1 with sensitivity of 877 μA/mmol L−1, detection limit of 3.09 nmol L−1 and limit of quantification 10.31 nmol L−1. Furthermore, the recovery results of real blood serum samples proved excellent using the proposed composite which makes it a potential candidate for PY routine analysis.

Investigation of the Effect of Yttrium Oxide Nanoparticles Doped with Cerium and Neodymium on Electro-Optics of Liquid Crystal Polymer Composites

Morphology and properties of liquid crystal polymer composites doped with inorganic nanoparticles are described. These composites comprised nematic liquid crystal 5CB, polyvinyl acetate, and nanoparticles of oxides (Y2O3, CeO2:Y2O3, and Nd2O3:Y2O3). Nanopowders were synthesized by the laser method of vaporization of a solid target under CO2-laser or fiber ytterbium laser irradiation. The effect of oxides on the electro-optical properties of the composites and times of response to an electrical pulse is investigated. It is shown that incorporation of CeO2:Y2O3 nanopowder in liquid crystal polymer composites affects the decrease of the control field and the increase of light transmission in an electric field stronger than incorporation of Nd2O3:Y2O3 nanoparticles.