Liquid Crystalline Matrix Research Articles

Limitation and Potential of Lignin-Assisted Stabilisation of Oriented Liquid Crystalline Cellulosic Mesophase

This study aimed at progressing in the fundamental understanding of the lignin-assisted microstructural stabilisation observed in solution-processed materials based on the polymer blend of hydroxypropyl cellulose and hardwood organosolv lignin. Mechanical analysis, polarised infrared spectroscopy and wide-angle X-ray scattering of shear cast blend films revealed that the effect of lignin on the flow-oriented cellulosic mesophase is also valid for blends composed of ethyl cellulose as liquid crystalline matrix polymer and lignin derived oligomers from base-catalysed depolymerisation as dispersed “microstructural cementing agent”. The results underline the significant role of the solvent diffusion between the continuous cellulosic and the dispersed lignin phase, which is ascribed to polymer-/oligomer-solvent interactions. An abundance of the solvent within the lignin phase caused the disruption of the microstructural stabilisation effect. The concept of a balanced proton-donor activity was introduced linking the solvent diffusion with the lyotropic liquid crystalline phase formation, the macro- and microstructural blend morphology and aspects regarding the solution processing.

Crystallization-driven tuneable lasing of perylene doped into the nematic liquid crystal

Versatile devices with tunable capabilities for controlling lasing wavelength and intensity are in high demand. Liquid crystals (LCs) exhibit immense potential for such applications, offering fine-tuning possibilities through external factors. On the other hand, laser technology is currently a research hotspot in optoelectronics, and also in practical applications. The recent market introduction of laser television marks a significant stride toward making such advanced technology accessible in every household. In synergy with laser pumping, the LCs unquestionably can be rediscovered. This study presents a comprehensive investigation into the crystallization phenomenon within a host-guest device, compact in size, free from moving parts, and integrating the liquid crystalline (LC) matrix doped with 3,4,9,10-tetra-(3-alcoxy-carbonyl)-perylene (THCP) dye. The focus lies in examining the influence of varying dye concentrations on multicolor fluorescence, lasing behavior, and device morphology. The systematic analysis of Random Lasing (RL) energy thresholds and the impact of DC voltage on light intensity modulation is demonstrated. Morphological changes were monitored in real-time using optical microscopy techniques, including crossed polarizer, and fluorescence imaging under 450 nm excitation. Utilizing advanced Transmission Electron Microscopy (TEM) techniques, we explore exceptional insights into our set of devices, providing novel information about the THCP crystallization process for the first time in the literature. To gain a comprehensive understanding of the crystal forming and molecular geometry we examined additionally the THCP dye, using X-ray diffraction and Raman spectroscopy. Furthermore, we showcase that varying the pumping energy enables multicolor tuning in the fabricated systems, presenting an attractive feature in the context of laser display technologies.

On an incompressible inertial nematic electrolyte model of liquid crystal flow

ABSTRACT We study the Cauchy problem of the new model of the three dimensional inertial nematic electrolyte, which models the N-species charged particles diffuse and advect in the nematic liquid crystalline matrix. This new model was proposed by [Calderer MC, Golovaty D, Lavrentovich O, et al. Modeling of nematic electrolytes and nonlinear electroosmosis. SIAM J Appl Math. 2016;76:2260–2285. doi: 10.1137/16M1056225]. The inertial effect is such that the system involves a hyperbolic feature. We first derive the local existence in large initial data when the flow is isotropy, i.e. λ = 1 . For the anisotropy case ( λ > 0 , λ ≠ 1 ), we obtain small data local solutions. Then, by seeking some further dissipative mechanisms from the elliptic structures, the local solution can be extended globally near the constant states with electro-neutrality condition.

Synthesis of mesogen-nanoparticle composites by doping 4-decyloxybenzoic acid with substrate-functionalized ZnO nanoparticle

Nanomaterials and Mesogenic materials are two important pillars of today’s science and technology, in the fields of both material and biological applications. Mesogens or liquid crystals (LC) are self-aggregated anisotropic fluids with long range order, and the nature of self-aggregation largely controls their physical and material properties. Doping of nanomaterials over liquid crystalline matrix can provide valuable tools for development of materials with new or improved properties. In the present work 4-decyloxybenzoic acid is taken as the mesogenic matrix. It is observed that, composite prepared by doping of 4-decyloxybenzoic acid mesogen matrix by ZnO nanoparticle pre-functionalized with the same mesogen, caused a marked alteration in the mesogenic behavior. With 3% doping of matrix pre-functionalized ZnO NP on 4- decyloxy benzoic acid, we could achieve a shift of about 31ºC in the N-Iso transition temperature and, a decrease of >10ºC for the onset of liquid crystallinity by this method without quenching any of the mesophases exhibited by the pure mesogen. The synthesized materials have been characterized by variable temperature Polarised optical microscopy (POM), DSC, FTIR, XRD, EDX, and TEM This process may be considered for preparation other nanoparticle-mesogen composites as well. It was observed that, the effect of doping on the transition temperature and enthalpy of 4-Decyloxybenzoic Acid can be significantly enhanced by pre-functionalizing the dopant (ZnO NP) with the substrate molecules and then mixing this substrate functionalized ZnO nanoparticle with the bulk substrate.

White Lasing and White Fluorescence from the Simplified Two‐Dyes Organic System

AbstractThe invention of lasers, which took place a few decades ago, marks a milestone in the past, present, and future technologies in optoelectronics. In particular, the colorful and white tones produced by lasers are appealing from a utilization standpoint and align well with human eye perception. In this paper, an idea for a white laser based on the attractive perylene family of luminescent dyes is introduced. This concept provides multicolor emission and brilliant photostability upon external optical pumping. The main advantage of the approach is the construction of a fully organic and two‐component white laser. The versatility of the system is demonstrated by assembling multicolor, tunable, and efficient fluorescent systems using a liquid crystalline matrix, which is supported by comprehensive experimental studies. Additionally, by utilizing laser spectroscopy techniques, it is able to narrow the emission bandwidth and enhance the light in a typical synthetic polymeric matrix. This leads to the realization of white lasing emission with just two luminescent dyes: perylene blue and perylene orange.

A Mechanistic Study on the Fluidization and Enhancement Effects of Cineole Toward Stratum Corneum Intercellular Lamellar Lipids: A Liquid Crystalline Model Approach.

The stratum corneum (SC) serves as the primary barrier for permeation in human skin. Penetration enhancers, such as 1,8-cineole, are utilized to enhance the permeation of drugs. Cineole increases the permeation of chemicals through different mechanisms. However, its mechanism, particularly at high concentrations, has not been well-studied and is the subject of the present investigation. In continuation of our previous studies, the present investigation aims to elucidate the mechanism of action and concentration dependency of the effects of 1,8-cineole on the structure, diffusional properties, and partitioning behavior of the SC at high concentrations. This will be achieved through lamellar liquid crystalline models and ex-vivo skin studies. A lamellar liquid crystalline lipid matrix model in the presence (25 - 90%, w/w) and absence of cineole was prepared from SC lipids and characterized by X-ray diffraction, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and polarized light microscopy (PLM) studies. Release of the model lipophilic drug (diazepam) from cineole and cineole-treated matrices and the permeation of the drug from cineole and cineole-containing matrices (as a vehicle similar to the stratum corneum lipids) through excised rat skin were studied. Drug assay was performed by HPLC. The PLM, DSC, and X-ray studies showed that the model matrix had a lamellar gel-liquid crystalline structure, and cineole fluidized the structure concentration-dependently and created other mesomorphic textures, such as myelinic figures. Release experiments showed that diffusion coefficients remained almost constant at high cineole concentrations of 40-90%, suggesting similar fluidization states. Skin permeation studies indicated that the diffusion coefficient (estimated from lag-time) increased concentration-dependently and played a role in permeability coefficient (Kp) increments alongside the increased partitioning of the model drug into the skin. Data suggest that high concentrations of cineole at the skin surface might not provide enough cineole in the skin for full fluidization, despite the similarity of the vehicle to SC lipids and even at high concentrations. The enhancement effect of cineole is concentration-dependent and might reach maximum fluidization at certain concentrations, but this maximum might not be easily achievable when cineole is used in formulations as pure or in a vehicle.

A Mechanistic Study on the Fluidization and Enhancement Effects of Cineole Toward Stratum Corneum Intercellular Lamellar Lipids: A Liquid Crystalline Model Approach

Background: The stratum corneum (SC) serves as the primary barrier for permeation in human skin. Penetration enhancers, such as 1,8-cineole, are utilized to enhance the permeation of drugs. Cineole increases the permeation of chemicals through different mechanisms. However, its mechanism, particularly at high concentrations, has not been well-studied and is the subject of the present investigation. Objectives: In continuation of our previous studies, the present investigation aims to elucidate the mechanism of action and concentration dependency of the effects of 1,8-cineole on the structure, diffusional properties, and partitioning behavior of the SC at high concentrations. This will be achieved through lamellar liquid crystalline models and ex-vivo skin studies. Methods: A lamellar liquid crystalline lipid matrix model in the presence (25 - 90%, w/w) and absence of cineole was prepared from SC lipids and characterized by X-ray diffraction, differential scanning calorimetry (DSC), Thermogravimetric Analysis (TGA), and Polarized Light Microscopy (PLM) studies. The release of the model lipophilic drug (diazepam) from cineole and cineole-treated matrices and the permeation of the drug from cineole and cineole-containing matrices (as a vehicle similar to the stratum corneum lipids) through excised rat skin were studied. A drug assay was performed by HPLC. Results: The PLM, DSC, and X-ray studies showed that the model matrix had a lamellar gel-liquid crystalline structure, and cineole fluidized the structure concentration dependently and created other mesomorphic textures, such as myelinic figures. Release experiments showed that diffusion coefficients remained almost constant at high cineole concentrations of 40-90%, suggesting similar fluidization states. Skin permeation studies indicated that the diffusion coefficient (estimated from lag-time) increased concentration-dependently and played a role in permeability coefficient (Kp) increments alongside the increased partitioning of the model drug into the skin. Data suggest that high concentrations of cineole at the skin surface might not provide enough cineole in the skin for full fluidization, despite the similarity of the vehicle to SC lipids and even at high concentrations. Conclusions: The enhancement effect of cineole is concentration-dependent and might reach maximum fluidization at certain concentrations, but this maximum might not be easily achievable when cineole is used in formulations as pure or in a vehicle.

Effects of Dispersed Carbon Nanotubes and Emerging Supramolecular Structures on Phase Transitions in Liquid Crystals: Physico-Chemical Aspects

The current state of the study of different liquid crystalline (LC) systems doped with carbon nanotubes (CNTs) is discussed. An attempt is endeavored to outline the state-of-the-art technology that has emerged after two past decades. Systematization and analysis are presented for the integration of single- and multi-walled carbon nanotubes in thermotropic (nematic, smectic, cholesteric, ferroelectric, etc.) and lyotropic LCs. Special attention is paid to the effects of alignment and supramolecular organization resulting from orientational coupling between CNTs and the LC matrix. The effects of the specific inter-molecular and inter-particle interactions and intriguing microstructural, electromagnetic, percolation, optical, and electro-optical properties are also discussed.

Electrooptical switching and photopatterning of luminescence in nematic liquid crystals doped with mesogenic europium complex

Stimuli-responsive self-organized soft matter such as liquid crystals, polymers, gels attracts great attention due to a variety of possible applications in modern technologies. Electroinduced hydrodynamic (EHD) instability in liquid crystals is one of long-discovered effects that shows a great potential for future applications. However, this effect is insufficiently studied and its practical implementation has yet to be found. In the present paper, we applied an EHD instability to tuning luminescent properties of nematic mixtures doped with a highly emissive europium complex, which has good solubility in a liquid crystalline (LC) matrix and high quantum yield of luminescence. Nematic mixtures studied in this work possess negative anisotropy of dielectric constant and positive anisotropy of conductivity that allow for observing convective EHD patterns induced by ionic conductivity. The influence of field frequency on the threshold voltage was studied and optimal conditions for induction of EHD patterns were determined. The luminescence intensity was found to substantially decrease or increase under an applied electric field depending on the alignment behavior of LC molecules inside the cells and the angle of observation. In a tilted cell (60°), the emission intensity gradually increases under applied electric field and reaches values ca. 2.5 times higher than in zero field conditions. This phenomenon is associated with alignment of the europium complex molecules along electric field direction (cooperatively with LC molecules) and EHD-induced light scattering. Kinetics of electrooptic switching was studied and different approaches to luminescence photopatterning of the studied nematic mixture with polymerizable monoacrylate and diacrylate were demonstrated.

Liquid crystalline matrix-induced viscoelastic mechanical stimulation modulates activation and phenotypes of macrophage.

Accumulating evidence indicates that the mechanical microenvironment exerts profound influences on inflammation and immune modulation, which are likely to be key factors in successful tissue regeneration. The elastic modulus (Em) of the matrix may be a useful adjustable property to control macrophage activation and the overall inflammatory response. This study constituted a series of Em-tunable liquid crystalline cell model (HpCEs) resembling the viscoelastic characteristic of ECM and explored how mechanical microenvironment induced by liquid crystalline soft matter matrix affected macrophage activation and phenotypes. We have shown that HpCEs prepared in this work exhibited typical cholesteric liquid crystal phase and distinct viscoelastic rheological characteristics. All liquid crystalline HpCE matrices facilitated macrophages growth and maintained cell activity. Macrophages in lower-Em HpCE matrices were more likely to polarize toward the pro-inflammatory M1 phenotype. Conversely, the higher-Em HpCEs induced macrophages into an elongated shape and upregulated M2-related markers. Furthermore, the higher-Em HpCEs (HpCE-O1, HpCE-H2, HpCE-H1) could coax sequential polarization states of RAW264.7 from a classically activated "M1" state toward alternatively activated "M2" state in middle and later stage of cell culture (within 3-7 days in this work), suggesting that the HpCE-based strategies could manipulate the local immune microenvironment and promote the dominance of the pro-inflammatory signals in early stages, while M2 macrophages in later stages. The liquid crystalline soft mode fabricated in this work maybe offer a new design guideline for in vitro cell models and applications.

Phase behavior of soybean phosphatidylcholine and glycerol dioleate in hydrated and dehydrated states studied by small-angle X-ray scattering.

Soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) form liquid crystal nanostructures in aqueous environments, and their mixtures can effectively encapsulate active pharmaceutical ingredients (API). When used in a subcutaneous environment, the liquid crystalline matrix gradually hydrates and degrades in the tissue whilst slowly releasing the API. Hydration dependent SPC/GDO phase behavior is complex, non-trivial, and still not fully understood. A deeper understanding of this system is important for controlling its function in drug delivery applications. The phase behavior of the mixture of SPC/GDO/water was studied as a function of hydration and lipid ratio. Small-angle X-ray scattering (SAXS) was used to identify space groups in liquid crystalline phases and to get detailed structural information on the isotropic reverse micellar phase. The reported pseudo ternary phase diagram includes eight different phases and numerous multiphase regions in a thermodynamically consistent way. For mixtures with SPC as the predominant component, the system presents a reverse hexagonal, lamellar and R3m phase. For mixtures with lower SPC concentrations, reverse cubic (Fd3m and Pm3n) as well as intermediate and isotropic micellar phases were identified. By modeling the SAXS data using a core-shell approach, the properties of the isotropic micellar phase were studied in detail as a function of concentration. Moreover, SAXS analysis of other phases revealed new structural features in relation to lipid-water interactions. The new improved ternary phase diagram offers valuable insight into the complex phase behavior of the SPC/GDO system. The detailed structural information is important for understanding what APIs can be incorporated in the liquid crystal structure.

Human-muscle-inspired single fibre actuator with reversible percolation

Artificial muscles are indispensable components for next-generation robotics capable of mimicking sophisticated movements of living systems. However, an optimal combination of actuation parameters, including strain, stress, energy density and high mechanical strength, is required for their practical applications. Here we report mammalian-skeletal-muscle-inspired single fibres and bundles with large and strong contractive actuation. The use of exfoliated graphene fillers within a uniaxial liquid crystalline matrix enables photothermal actuation with large work capacity and rapid response. Moreover, the reversible percolation of graphene fillers induced by the thermodynamic conformational transition of mesoscale structures can be in situ monitored by electrical switching. Such a dynamic percolation behaviour effectively strengthens the mechanical properties of the actuator fibres, particularly in the contracted actuation state, enabling mammalian-muscle-like reliable reversible actuation. Taking advantage of a mechanically compliant fibre structure, smart actuators are readily integrated into strong bundles as well as high-power soft robotics with light-driven remote control.

Interface mechanics of liquid crystal polymer nanocomposites with high concentrations of MWCNTs

Compositing a liquid crystal polymer (LCP) with highly oriented multi-walled carbon nanotubes (MWCNTs) at non-dilute filler concentrations has attracted considerable attention due to its function as alignment layer as well as mechanical reinforcement. In this study, the structural and mechanical features of the LCP–MWCNT interface were investigated by all-atom molecular dynamics (MD) simulations. The results suggested that the MWCNT filler co-oriented with the liquid crystalline matrix enhances the crystallinity of the LCP molecules, especially in the interfacial area. The aromatic rings of the LCP components exhibited a repeating structural pattern because of the different equilibrium distances depending on the type of π-π stacking. The effect of the morphological change of LCPs in the interfacial region on the load transfer capability was also evaluated in terms of filler concentrations. In particular, tight coupling between the liquid crystal components and efficient load transfer to the outermost nanotube shell were first identified. These features account for the enhanced mechanical stiffness in the transverse loading direction with increasing volume fraction of the MWCNTs, as confirmed experimentally.

Tuneable helices of plasmonic nanoparticles using liquid crystal templates: molecular dynamics investigation of an unusual odd-even effect in liquid crystalline dimers.

Liquid crystalline (LC) dimers formed helical nanofilaments depending on the parity of the alkyl linker, revealing an unusual odd-even effect. Molecular dynamics simulations were used to investigate the observed tendency. Elongation of the linker translates to an increase of the pitch of the helices, which allows achieving tuneable helical assemblies of Au nanoparticles doped to the LC matrix. The impact of the tuneable pitch of helices on the chiral optical properties of composites was investigated with full-wave simulations based on the T-matrix method.

Insights into the Formation Pathway of Templated Ordered Nanostructured Carbonaceous Particles under Hydrothermal Conditions.

Ordered nanostructured materials and their porous counterparts are important for numerous applications in sorption and separation sciences, electrochemistry, catalysis, and photonics. They can be synthesized by introducing surfactant or amphiphilic polymer template(s) into the condensation stage of a developing solid. Understanding the pathways involved in the formation of these materials is of great interest and will help in the development of future synthesis schemes for designing nanomaterials with controlled nanostructures, pore sizes and shapes, and particle morphologies. In this work, the formation pathway of carbonaceous particles, with cubic-type ordered nanostructures, in the polymer amphiphile-templated hydrothermal condensation of sugar was investigated. A detailed transmission electron microscopy study revealed the initial formation of ∼50 nm sized nanoparticles and the structure attributable to assembled nanoparticles to form larger microparticle volumes. Small-angle X-ray scattering analysis showed the time-dependent development of the ordered structures in the carbonaceous particles. A dynamic stabilization-destabilization of the ordered phase was suggested through the analysis of the liquid crystalline gel-like matrix. The growing carbonaceous body inherited the final liquid crystalline phase, giving the microparticles a well-ordered cubic nanostructure. An additional internal domain texture was also revealed inside the microparticles. The proposed pathway will contribute toward establishing strategies for precisely manipulating nanostructured bodies as well as acquiring an in-depth understanding of the templated precipitations, including those in the natural systems.

Modifications of FLC Physical Properties through Doping with Fe2O3 Nanoparticles (Part I).

The aim of this paper is to show, by systematic studies, the influence of γ-Fe2O3 nanoparticles on the physical parameters of the liquid crystalline matrix, exhibiting a ferroelectric phase in a wide temperature range. The detailed research was carried out by using diffraction (PXRD), microscopic (OM, SEM, FCPM, POM), thermal (DSC), optical (TLI), electric and spectroscopic (FTIR) methods. We show that even the smallest concentration of γ-Fe2O3 nanoparticles largely modifies the parameters of the ferroelectric SmC* phase, such as spontaneous polarization, switching time, tilt angle, rotational viscosity, dispersion anchoring energy coefficient and helix pitch. The admixture also causes a significant reduction in the temperature of phase transitions, broadening the SmA* phase at the expense of the SmC* phase and strong streaking of the texture. We present and explain the non-monotonic modification of these parameters with an increase in the nanoparticle concentration. The influence of oleic acid admixture on these parameters is also widely discussed. We have shown that certain parameters of organic-metal nanocomposites can be controlled by the appropriate amount of metal admixture.

Optical UV Dosimeters Based on Photoracemization of (R)‐(+)‐1,1′‐Bi(2‐Napthol) (BINOL) within a Chiral Nematic Liquid Crystalline Matrix

AbstractAccurate and low‐cost wearable or portable monitors for personal solar ultraviolet (UV) exposure are of interest to reduce the risk of adverse UV effects such as eye diseases, sunburn and skin cancer. Here, a novel sensor involving the racemization of a chiral dopant within a nematic liquid crystalline matrix is described, and the suitability of these sensors to act as personal UV dosimeters is explored. It was shown that these sensors respond to UV light with a significant change in the position of the reflection band of the chiral nematic liquid crystal. The sensitivity of these sensors is shown to be 0.23 nm/mJcm−2. This corresponds to a change of 80 nm over a dose equivalent to two hours of solar exposure.

Comparison of quenching efficacy of SYBR Green I and PicoGreen fluorescence by ultrasmall gold nanoparticles in isotropic and liquid-crystalline DNA systems

Gold nanoparticles (GNPs) are promising for sensors based on fluorescence quenching. Conjunction of GNPs to liquid crystalline (LC) matrix may improve their quenching properties. In the present work the quenching of SYBR Green I (SG) and PicoGreen (PG) fluorescence by negatively charged 2.5 nm GNPs was investigated in an isotropic DNA solution and in its cholesteric liquid crystalline dispersion (DNA CLCD). These dyes have similar chromophore structures and spectral properties but different charges: +2 (SG) and +3 (PG). The most efficient static fluorescence quenching was observed at the lowest concentration of dyes: in the DNA CLCD for SG (KSV = 7.4 × 107 M−1) and in the isotropic DNA solution for PG (KSV = 1.54 × 108 M−1). Since in the DNA solution quenching was due to the formation of a non-fluorescent complex with GNPs, the quenching was up to ~70-fold more efficient for PG than for SG. In the DNA CLCD the quenching efficacy of SG fluorescence increased up to ~15-fold because of the energy transfer. At the same time, due to steric hindrance for the interaction of PG with GNPs in the DNA CLCD caused by tight packaging of DNA molecules, the fluorescence quenching efficacy was ~5-fold higher in the isotropic solution.

Photoluminescence of CdSe and CdSe/ZnS Quantum Dots in Amorphous and Liquid-Crystalline Polymer Matrices

The influence of the structure of the polymer matrix on the main photoluminescence characteristics of composites based on core (CdSe) and core–shell type (CdSe/ZnS) quantum dots embedded in liquid-crystalline and amorphous polymers of similar chemical structure is studied. The photoluminescence spectra consist of two bands (2.15 and 1.70 eV), the first of which corresponds to the radiative recombination of excitons, and the second one corresponds to carriers captured by traps at the quantum dot boundary. The second band is absent in the case of CdSe/ZnS quantum dots embedded in the liquid-crystalline polymer matrix. The kinetics of photoluminescence is well described by the sum of two decaying exponentials for CdSe quantum dots in matrices of both types and CdSe/ZnS quantum dots in the amorphous matrix. To determine the photoluminescence kinetics in the case of CdSe/ZnS quantum dots in the liquid-crystalline matrix, one exponential is sufficient. These effects are explained by the appearance of regions with closely spaced quantum dots, in which, in particular, the resonance transmission of excitation is possible.

Incorporation of magnesium oxide nanoparticles in to nematic liquid crystalline matrix

Incorporation of magnesium oxide nano particles (MgONPs) in a nematic liquid crystal display material namely 4-pentyl-4'-cyanobiphenyl (5CB) have been analyzed by differential scanning calorimeter, polarizing light microscopy and dielectric spectroscopy. MgONPs have been dispersed in two different concentrations in pure 5CB viz. 0.2 and 0.6 wt%. It has been experimentally noticed that with the increase of MgONPs concentrations in 5CB, the nematic to isotropic transition temperatures decreases and dielectric anisotropy increases. Relaxation frequency of an observed relaxation mode corresponding to molecular rotation about the short axis is almost unchanged after dispersion of MgONPs. The ionic conductivity has increased by approximately one order of magnitude for 0.6 wt% MgONPs and decreased for 0.2 wt%.