Liquid Crystalline Properties Research Articles

Pluronic P123/DMSO Lyotropic Liquid Crystal for Incorporating Bioactive Substances for Topical Application.

Lyotropic liquid crystals (LLCs) have attracted considerably growing interest in drug delivery applications over the last years. The structure of LLC matrices is complementary to cell membranes and provides an efficient, controlled, and selective release of drugs. In this work, a complex of experimental methods was used to characterize binary LLCs Pluronic P123/DMSO and triple LLC systems Pluronic P123/DMSO/Ibuprofen, which are interesting as transdermal drug delivery systems. Liquid crystalline, thermal, and rheological properties of LLCs were studied. Concentration and temperature areas of the lyomesophase existence were found, and phase transition enthalpies were evaluated. Intermolecular interactions among the components were studied by infrared (IR) spectroscopy. In vitro studies of Ibuprofen (Ibu) release from various LLCs allow differentiation of its release depending on the polymer content. Atomic force microscopy and contact angle methods were used to characterize the surface morphology of the hydrophobic membrane, which was used as a stratum corneum model, and also evaluate the adhesion work of the LLCs. A complex analysis of the results provided by these experimental methods allowed revealing correlations between the phase behavior and rheological characteristics of the LLCs and release kinetics of ibuprofen. The proposed biocompatible systems have considerable potential for a transdermal delivery of bioactive substances.

Synthesis, characterization and investigation of liquid crystalline properties for some cross-link polymers containing melamine

Synthesis, characterization and investigation of liquid crystalline properties for some cross-link polymers containing melamine

Synthesis and characterization of grafted graphene oxide materials with lyotropic liquid crystalline properties detected by NMR spectroscopy

Grafted derivatives of graphene oxide (GO), namely N-vinyl-2-pyrrolidone grafted-GO (GO-g-NVP) and oleic acid grafted-GO (GO-g-OLA) were prepared by heating GO in the presence of the corresponding vinyl monomers and the AIBN radical initiator. The lyotropic mesogenic behavior of GO-g-NVP and GO-g-OLA in DMSO‑d6 was proved by deuterium NMR spectroscopy, showing these materials could be used as alignment media for obtaining NMR anisotropic parameters in organic solvent.

Controlling the Nematic Liquid Crystallinity of Cellulose Nanocrystals with an Alcohol Ethoxy Sulfonate Surfactant.

Cellulose nanocrystals (CNCs) are biobased colloidal nanorods that have unlocked new opportunities in the area of sustainable functional nanomaterials including structural films and coatings, biomedical devices, energy, sensing, and composite materials. While selective light reflection and sensing develop from the typical chiral nematic (cholesteric, Nem*) liquid crystallinity exhibited by CNCs, a wealth of technologies would benefit from a nematic liquid crystal (LC) with CNC uniaxial alignment. Therefore, this study answers the central question of whether surfactant complexation suppresses CNC chirality in favor of nematic lyotropic and thermotropic liquid crystallinity. Therein, we use a common surfactant having both nonionic and anionic blocks, namely, oligo(ethylene glycol) alkyl-3-sulfopropyl diether potassium salt (an alcohol ethoxy sulfonate (AES)). AES forms complexes with CNCs in toluene (a representative for nonpolar organic solvent) via hydrogen bonding with an AES' oligo(ethylene glycol) block. A sufficiently high AES weight fraction endows the dispersibility of CNC in toluene. Lyotropic liquid crystallinity with Schlieren textures containing two- and four-point brush defects is observed in polarized optical microscopy (POM), along with the suppression of the cholesteric fingerprint textures. The results suggest a nematic (Nem) phase in toluene. Moreover, thermotropic liquid crystallinity is observed by incorporating an excess of AES, in the absence of an additional solvent and upon mild heating. The Schlieren textures suggest a nematic system that undergoes uniaxial alignment under mild shear. Importantly, replacing AES with a corresponding nonionic surfactant does not lead to liquid crystalline properties, suggesting electrostatic structural control of the charged end group of AES. Overall, we introduce a new avenue to suppress CNC chirality to achieve nematic structures, which resolves the long-sought uniaxial alignment of CNCs in filaments, composite materials, and optical devices.

Size-dependent optical and dielectric anisotropy of CdS nanowire doped high-birefringent nematic liquid crystalline compound

Highly birefringent liquid crystals have grabbed ample attention because of their potential applications as an active medium for devices in visible, infrared and other spectral regions. Here, we have attempted to study the effect of the size and concentration of CdS nanowires on a nematic liquid crystal. Anisotropy in liquid crystals is one of those distinguishing traits that gain their superiority over other materials. We hereby have analyzed how optical and dielectric anisotropy respond to variations in the size and concentration of the dopant. The study is of significant scientific value because there is very little literature available on how dopant size can alter liquid crystalline properties and also introduces a method to tune the properties of pure liquid crystals (LCs) by varying the size and concentration of the dopant. The study explains how the size of the nanowires changes the analyzed parameters and up to what extent. The obtained results yield a significant increase in both optical and dielectric anisotropy by doping CdS nanowires making them an excellent choice for dopant selection. CdS-doped nematic LC mixtures have proved to be highly birefringent and possess a high positive dielectric anisotropy as well. Such a compound can be of great application in device fabrications such as laser beam steerers, electronic lenses, attenuators and light shutters, etc.

Naphthalene-based symmetrical liquid crystalline dimers: Synthesis, characterization, mesomorphic behaviour and DFT studies

The reactions of different α,ω-dibromo alkanes with (E)-4-(naphthalen-2-yldiazenyl)phenol and (E)-4-(naphthalen-2-ylimino)methyl)phenol, respectively, led to the synthesis of two new homologous series of liquid crystalline symmetrical dimers with azobenzene or azomethine central linkage and containing the naphthalene moiety as a rigid core. Spectroscopic techniques like FT-IR, 1H NMR, 13C NMR and elemental analysis confirmed their structure. These dimers exhibited mesomorphic phases, studied through POM and DSC. Their photophysical behaviour was explored using UV–visible spectroscopy. Remarkably, dimers with even spacer units (n = 2, 4, 6, 8, 10, 12) displayed excellent liquid crystalline properties as nematic phases, with extended mesophase lengths and thermal stability for both series. The study revealed the vital role of spacer length in determining liquid crystalline behaviour. The computational studies employed the B3LYP method and electron density method for optimization.

Revisiting Dimorphs of 4-n-octyloxybenzoic Acid: Contrasting Mechanical Property and Surface Wettability.

4-n-octyloxy benzoic acid is known to exhibit liquid crystalline properties, and under normal pressure and temperature conditions, it exists as at least two crystalline polymorphs. We revisited the system and discovered that single crystals of one of the polymorphs display plastic deformation, whereas the other is brittle. n-octyl chains are arranged in an end-to-end fashion, forming slip planes in the plastically deformable polymorph, whereas they are interdigitated in the crystal structure of the brittle polymorph. Due to the difference in the arrangement of the -COOH group and alkyl chains, the major faces of the crystals of both polymorphs possess significant differences in the wettability towards moisture.

Palladium-Catalyzed Annulative π-Extension of Bay-Iodinated Triphenylenes to Access Polycyclic Aromatic Compounds.

A palladium-catalyzed annulative π-extension reaction of bay-iodinated triphenylenes with aryl iodides/o-chloroaromatic carboxylic acids was developed. This approach enabled the synthesis of diverse polycyclic aromatic compounds, including dibenzo[fg,op]tetracenes, azadibenzo[fg,op]tetracenes, and tribenzo[a,g,m]coronenes. Initial studies indicate that the resulting product, 2,3,8,9,14,15-hexakis(decyloxy)tribenzo[a,g,m]coronene, exhibits good liquid-crystalline properties.

Preparation and properties of highly flexible cholesteric side-chain liquid crystalline elastomers with selective reflective properties in the visible region

ABSTRACT In this paper, we have synthesised cholesteryl 4-allyloxybenzoate (MB), crosslinking agent dodecane-1,12-diyl bis(undec-10-enoate) (MG), and A’BGF series liquid crystalline elastomer (LCE) films which take polymethylhydrosiloxane (A’) as the backbone, MB as the cholesteric liquid crystal (LC) monomer, and MG and bis-vinyl silicone oil (MF) with different reactivities as cross-linking agent for exploring the effect of the change of MF content on the properties of the elastomeric films. The experimental results show that the synthesised MB, MG, and the LCE films are all consistent with the molecular design; MB is an enantiotropic cholesteric LC. The synthesised LCE films are cholesteric LCs, have certain selective reflection characteristic, higher thermal stability, and their Tg decreased down to 3.9°C as MF increasing. During the heating and cooling, the liquid crystalline properties of the LCE films have a good reversibility. Among the synthesised LCE films, A’BGF-2 has stretching radio of 264.8% at room temperature, with the best elastic properties. By adjusting the ratio of MF, the content of small-molecule MB remained in the films can be changed, which will affect the optical properties and elasticity of the LCE films. The experiments provide a method for the preparation of highly elastic side chain LCE film.

Fabrication of Hierarchical Assemblies through Temperature-Triggered Liquid Crystallization Driven Self-Assembly.

Functional hierarchy is prevalent in biological systems owing to natural evolution. Efforts to replicate these structures in artificial materials have gained traction in materials science. Although artificial hierarchical structures are fabricated at different scales based on site-specific interactions using ABC-type block copolymers (BCPs), the fabrication of such hierarchical structures using AB-type BCPs via a simple and efficient method remains challenging. Herein, a class of amphiphilic BCPs (PDenm -b-PACholn ) is reported comprising dendronized oligoethylene glycol (Den) and cholesterol (AChol) as hydrophilic and hydrophobic moieties, respectively. By employing the collapse of PDenm blocks at a specific temperature, the fabrication of bundled fibers and multilayer vesicles is achieved with an obvious hierarchy. Different from common reversible aggregation-disaggregation processes of thermal-responsive polymers, the ordering of the core-forming block with liquid crystalline (LC) properties provides robustly physical cross-linking, coupled with epitaxial growth and the lateral fusion of LC blocks, guiding the formation of stable hierarchical micellar structures. It is highlighted that the combination of temperature-sensitive properties and LC ordering alignment offers a novel approach for constructing hierarchical structures using AB-type BCPs via an efficient one-step assembly method.

Magnetorheological liquid-crystalline polymers with magnetic tetrachloroferrate ions based on polyvinyl chloride

ABSTRACT Novel magnetic ionic polymers based on polyvinyl chloride ([PVCs][FeCl4]) with liquid-crystalline (LC) ordering were synthetised and characterised. The [PVCs][FeCl4] containing magnetic tetrachloroferrate ions were prepared with PVC, pyridyl LC monomers and FeCl3. Various devices and instruments were used to characterise the chemical structure, thermal behaviour, magnetic properties, and LC properties. The synthetised [PVCs][FeCl4] showed smectic LC phase and presented excellent thermal stability. Several magnetorheological (MR) fluids were prepared using [PVCs][FeCl4] as particles and silicone oil as carrier fluid. MR Effects and settlement stability were investigated. Under the condition of external magnetic field, the MR fluids showed Bingham flow characteristics, and the MR effect was enhanced with increasing FeCl4 − content in the systems. Under the condition of magnetic field intensity of 80 kA/m and shear rate of 2.5 s−1, the magnetorheological efficiency of [PVCs][FeCl4] based MR fluids with particle concentration of 20% can reach up to 14.7. The excellent MR effect of [PVCs][FeCl4] was due to the strong coupling between the magnetic moment of the FeCl4 − anion and the orientation of cationic LC primitive under the action of an applied magnetic field. Furthermore, the good settling stability of the MR fluids was due to the introduction of organic mesogens, PVC main-chains and the ionic components for the [PVCs][FeCl4] particles.

Azo-linked room temperature columnar liquid crystals with bisphenol A core: Structure property relationship and photophysical properties

A series of bent-shaped liquid crystals containing an azo group and a bisphenol A core were synthesized, and characterized using various techniques. The presence of mesogenic properties in these azo-based dimers was confirmed through POM, DSC, and high-temperature XRD analysis. The structure-property relationship is further studied to confirmed the effect of the variable alkyl side chain on the terminal position, which also affects the liquid crystalline properties of the compounds in terms of mesophase temperature range and thermal stability. All the compounds exhibited enantiotropy columnar hexagonal phase with wide temperature range and thermal stability. Their photophysical properties were investigated using UV–visible spectroscopy and spectrofluorometry. It was observed that all four columnar mesogens underwent cis and trans azo isomerization upon exposure to photoisomerization.

Cholesterol-appended cyanostyryl thiophene positional isomers with multistimuli responsive emission switching and liquid crystalline properties

Cholesterol appended cyanostyryl thiophene derivatives were designed and synthesized to explore the multistimuli responsive solid state emission and liquid crystalline properties.

Synthesis and characterization of acrylamide substituted sulfanilamide based calamitic LCs: effect of terminal group on phase behavior

In the present study, we have prepared two phenyl ring substituted sulfanilamide bearing acrylamide linking groups. The four derivatives (C1-C4) were prepared by changing the left n-alkoxy terminal group. The liquid crystalline properties of the synthesized sulfanilamide-based compounds were investigated using POM and DSC studies. All four materials exhibit nematic liquid crystalline properties during both heating and cooling. They also demonstrate a broad temperature range and thermal stability. Further, we have studied the structure-property relationship to gain a better understanding of the effect of the linking group and variable alkoxy tail group on mesomorphic behavior. The results indicate that thermal stability, mesophase temperature range, and liquid crystalline properties depend on the linking group and variable alkyl chain length.

A one-pot telescopic synthesis of benzo[b]carbazoles and exploration of their liquid crystalline properties.

We describe a diversity-oriented one-pot telescopic synthesis of various benzo[b]carbazoles with the naphthannulation of indoles as the key step, enabled by an intramolecular furan-olefin Diels-Alder reaction. This strategy is general and efficient across a wide range of substrates. We applied this method to synthesize and characterize the first benzo[b]carbazole-based liquid crystalline materials, where the unique molecular design led to the formation of a rare nematic phase at room temperature.

Useful synthetic artifacts? The impact of ubiquitous linker-adjacent groups on the self-assembly of discotic dimers.

Although discotic dimers commonly feature bulky ether substituents adjacent to the linking group, the impact of these chains on self-assembly remains unclear. A series of dibenzo[a,c]phenazine dimers with alkoxy groups ortho to the linker were prepared and their solution conformational dynamics and liquid crystalline properties examined. The presence of a methoxy substitutent adjacent to the bridging group increased the phase stability, whereas longer chains dramatically decreased clearing temperatures. NMR solution studies indicated that adjacent groups increased the preference of dimers to adopt unfolded conformers. DFT models indicated that the unfolded structures were nonplanar and hence less compatible with columnar ordering, leading to a destabilization of the mesophases.

Preparation and characterization of Schiff base and its complex with Cu(II) and study of their liquid crystalline properties.

The research includes the preparation of ligand E-H, and it was identified by spectroscopic methods Infra Red IR, Nuclear magnatic Reasonance NMR, Mass spectra· It was also prepared from the ligand a complexes with copper (11) and characterized by Infra Red spectra. Central metals ions and Schif base coordinated via O and N donor sites which was observed from IR spectra. The liquid crystal characteristics of the ligand was studied using polarized optical microscope POM and the ligand is a liquid crystal by showed nematic phase only, while no liquid crystal phase was detected in the prepared complex, and it disintegrated at 250°C.

Quantum-Chemical Approaches to Creation of Mesogenic Binuclear Europium(III) Complexes with Intensive Luminescence

This article contains data on the application of quantum-chemical methods for simulation of mesogenic binuclear complexes of europium(III) (Eu(III)) with substituted β-diketones and Lewis bases along with the possibility of prediction of their liquid crystalline (LC) properties. The relationships between geometric parameters of the complexes' molecules, the structural features of their coordination polyhedra and the probability of mesophase behavior were considered. According to the calculated parameters of Voronoi-Dirichlet polyhedra, the structural features of the first coordination sphere of Eu(III) complexes were studied and compared with the data for mononuclear complexes. Using the calculated energies of the ligands' excited states, the luminescence efficiency of the complexes was estimated. The results of quantum-chemical simulations provide recommendations for selection of ligand environment for the synthesis of LC binuclear Eu(III) complexes.

Smectic behaviour of α,ω-alkanediol diesters of a partially fluorinated 4-dodecyloxybenzoic acid: the odd-even effect

ABSTRACT Synthesis of a new series of mesogenic dimers and investigation of their liquid crystalline properties with thermal, optical and XRD methods is reported. Unlike dimeric mesogens studied to date, the presently reported dimers are derived from a single-ring mesogen containing a partially fluorinated dodecyl chain, which effects nanosegregation and formation of a lamellar phase. The reported four diesters with the odd-membered connecting alkyl chain exhibit a SmA phase. In contrast, two even-membered analogues have higher melting points and do not exhibit mesogenic behaviour.

Liquid-crystalline pillar[5]arene-based [2]rotaxanes

ABSTRACT Liquid-crystalline mechanically interlocked molecules have been prepared from a clickable pillar[5]arene-containing [2]rotaxane building block incorporating ethynylated stoppers and dendritic mesogenic subunits of generation 0, 1 and 2 under copper-catalysed alkyne-azide cycloaddition conditions. The liquid-crystalline properties of the resulting pillar[5]arene-based rotaxanes bearing 4, 8 and 16 peripheral cyanobiphenyl units have been investigated and compared to those of corresponding model compounds lacking the macrocyclic component.