Formation Of Liquid Crystalline Phase Research Articles

Nanotubes of a Different Kind: Stoichiometry and Geometry of the Orange II/γ-Cyclodextrin Complex in Water.

Orange II (O-II), a water-soluble ionic azo dye, aggregates and eventually forms needle-like crystals at concentrations greater than 0.15 M. However, when equimolar amounts of γ-cyclodextrin (γ-CD) are added to solutions containing O-II at 0.025 M or higher, the solution's appearance rapidly changes presenting a viscous, birefringent liquid, a lyotropic liquid crystalline solution. Birefringence is absent when viewing aqueous solutions of only O-II or γ-CD at concentrations greater than 0.03 M. Using ultraviolet-visible (UV-vis) and fluorescence spectroscopy, coupled with conductivity measurements, we postulate a structure for the basic "building block" of the self-assembly that eventually gives rise to a rodlike superstructure, leading to the formation of a lyotropic liquid crystalline phase.

Phase Behavior and Rheological Properties of Size-Fractionated MXene (Ti3C2Tx) Dispersions.

Understanding the dispersion behavior of MXenes is interesting from a fundamental colloid science perspective and critical to enabling the fluid-phase manufacturing of MXene devices with controlled microstructures and properties. However, the polydispersity, irregular shape, and charged surfaces of MXenes result in a complex phase behavior that is difficult to predict through theoretical calculations. As two-dimensional (2D) nanomaterials, MXenes can form lyotropic liquid crystal phases, gels, and aggregates. This work aims to elucidate the effects of MXene (Ti3C2Tx) sheet size on their phase behavior and associated rheological properties. Aqueous dispersions of large sheets with an average lateral dimension of 3.0 μm, small sheets with an average lateral dimension of 0.3 μm, and a bimodal mixture of the two sizes were investigated by using cross-polarized optical microscopy and rheology. At low concentrations, the large MXene dispersions exhibited lyotropic liquid crystal behavior and extended aligned textures, but increasing concentration resulted in the formation of dense flocs. Dispersions of small sheets formed small birefringent domains with increasing concentration but lacked long-range ordering. A bimodal mixture of these sizes enabled the formation of liquid crystalline phases with extended aligned textures with less floc formation. These results provide insights into using polydispersity to tune dispersion microstructure and rheological properties that can be applied to designing dispersions for fluid-phase manufacturing methods, such as direct ink writing.

Fabrication of Liquid Crystalline Polyurethane/Polyhedral Oligomeric Silsesquioxane Nanofibers via Electrospinning

A series of fibrous meshes based on liquid crystalline polyurethane/POSS composites were prepared. Two types of polyhedral oligomeric silsesquioxanes (POSSs) of different structures were chosen to show their influence on electrospun fibers: aromatic-substituted Trisilanolphenyl POSS (TSP-POSS) and isobutyl-substituted Trisilanolisobutyl POSS (TSI-POSS) in amounts of 2 and 6 wt%. The process parameters were selected so that the obtained materials showed the highest possible fiber integrity. Moreover, 20 wt% solutions of LCPU/POSS composites in hexafluoroisopropanol (HFIP) were found to give the best processability. The morphology of the obtained meshes showed significant dependencies between the type and amount of silsesquioxane nanoparticles and fiber morphology, as well as thermal and mechanical properties. In total, 2 wt%. POSS was found to enhance the mechanical properties of produced mesh without disrupting the fiber morphology. Higher concentrations of silsesquioxanes significantly increased the fibers’ diameters and their inhomogeneity, resulting in a lower mechanical response. A calorimetric study confirmed the existence of liquid crystalline phase formation.

Assembly of nanoparticles at symmetric coffee stain locations

The precise picture of the nanoparticle array deposits on the substrate surface is crucial since many uses for nanostructures are dependent on how the assembled array's collective behavior responds to various physicochemical properties. The well-known seed-mediated approach was used to synthesize gold nanorods stabilized by CTAB molecules. Due to the Helium Ion Microscope’s (HIM) remarkable ability to reveal the real nature of the deposited entities, gold nanorod arrays at symmetrical parts of the coffee-stain ring have been studied using this technique. The object of this study is to evaluate three different positions within the coffee-stain ring at the convective symmetric locations. In the context of the self-assembled mechanism, the formation of various liquid crystalline phases induced by the evaporating symmetric convective flow inside the sessile droplet have been examined and compared at the symmetric positions within the ring.

Micelle structure of nonionic surfactants containing carbon dioxide moieties in protic ionic liquids

Partial substitution of ethylene oxide with carbon dioxide moieties can yield greener nonionic surfactants with comparable functionalities. In water, studies showed that the incorporation of CO2 moieties suppresses the formation of liquid crystalline phases at high concentrations. A similar reduction in solvation and suppression of liquid crystal formation is observed here in the ionic liquids ethylammonium nitrate and propylammonium nitrate. Small-angle neutron scattering is used to study the solvation and packing of micelles in ionic liquids as functions of temperature, concentration, and content of CO2 moieties. By comparing with aqueous solutions, this work shows that while the nature of surfactant-solvent interaction is comparable among water and alkylammonium nitrate ILs, their behaviours in the solvated micelle shell are different. The lack of liquid crystalline phases should be attributed to the small excluded volume of micelles, which can be fine-tuned via ion design and choice of solvent.Graphical

Essential L-Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation

The colloidal 2D materials based on graphene and its modifications are of great interest when it comes to forming LC phases. These LC phases allow controlling the orientational order of colloidal particles, paving the way for the efficient processing of modified graphene with anisotropic properties. Here, we present the peculiarities of AA functionalization of GO, along with the formation of its LC phase and orientational behavior in an external magnetic field. We discuss the influence of pH on the GOLC, ultimately showing its pH-dependent behavior for GO-AA complexes. In addition, we observe different GO morphology changes due to the presence of AA functional groups, namely L-cysteine dimerization on the GO platform. The pH dependency of AA-functionalized LC phase of GO is examined for the first time. We believe that our studies will open new possibilities for applications in bionanotechnologies due to self‐assembling properties of LCs and magnificent properties of GO.

Effect of electrolytes on the sol–gel phase transitions in a Pluronic F127/carboxymethyl cellulose aqueous system: Phase map, rheology and NMR self-diffusion study

This investigation aims to obtain a thermosensitive platform useful for specific nanomedicine applications through the addition of suitable salts. An aqueous mixture consisting of the copolymer Pluronic F127 and sodium carboxymethyl-cellulose, in a ratio of 20/4 by weight, in the presence of different concentrations of Na2SO4, NaCl, and NaSCN, was investigated using the visual inversion tube approach to estimate a phase map, and then characterized through rheological measurements. The formation of a cubic liquid crystalline phase at temperatures higher than 37 °C was suggested in all systems. The complex viscosity, decreases in the presence of salts in the order Na2SO4 > NaCl > NaSCN with more marked effect for lower concentrations. Salt addition allows to tune the crowding effect of NaCMC. For the polymer mixture and for a sample containing NaCl, 1H NMR self-diffusion experiments display a non-mono-exponential decay of the echo signals of Pluronic F127, caused by the polydispersity of commercial Pluronic F127. The rheological properties along with the diffusion behaviour of the liquid crystal micelles suggest that a sample containing NaCl 0.07 mol/kg, with a sol-hard gel transition temperature around 35 °C, close to that of the body, may be a suitable and biocompatible thermosensitive platform to administer both hydrophobic and hydrophilic drugs such as antibiotics, anticancer drugs or growing factors.Synopsis: A simple thermoresponsive platform for drug delivery: Pluronic F127, NaCMC and NaCl.

Investigation of diclofenac release and dynamic structural behavior of non-lamellar liquid crystal formulations during in situ formation by UV–Vis imaging and SAXS

In situ formation of high viscous inverse lyotropic non-lamellar liquid crystalline phases is a promising approach for sustained drug delivery in the joint. The in situ forming process on exposure of two diclofenac-loaded preformulations to aqueous media was characterized with respect to depot size and shape, initial release and structural transitions using UV–Vis imaging and spatially and time-resolved synchrotron small-angle X-ray scattering (SAXS). The preformulations consisted of 10 % (w/w) ethanol, 10 % (w/w) water and a binary lipid mixture of glycerol monooleate (GMO):1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DOPG) or GMO:medium chain triglycerides (MCT). Upon injection of preformulations into an employed injection-cell containing excess of bio-relevant medium, rapid generation of liquid crystalline depots was observed. UV–Vis images and constructed 2D SAXS maps of the injection-cell showed depots with different shapes and sizes, and features with high nanostructural heterogeneity. More extensive swelling of the GMO:DOPG-based preformulation was observed compared to the GMO:MCT-based preformulation. The UV image analysis found that a higher amount of diclofenac was released in the image area after 20 h from the GMO:MCT depot compared to the GMO:DOPG depot. The injection-cell setup employing UV–Vis imaging and synchrotron SAXS constitutes an attractive approach for evaluating the in situ forming processes of liquid crystalline depots.

Aspect ratio dependent viscoelastic properties of graphene oxide liquid crystals

We present a systematic investigation of the size-dependent viscoelastic properties of aqueous suspensions of graphene oxide (GO). The study is performed on three different size graphene oxide dispersions with an average sheet surface area of 22.89, 126.42 and 173.83 μm2. The viscoelastic properties of the GO suspensions are found to be strongly dependent on the size of GO sheets. Irrespective of the size, all the GO dispersions revealed an isotropic phase at low volume fractions and a nematic liquid crystalline phase above critical volume fractions. The formation of nematic liquid crystalline phase strongly depends on the size of GO sheets. The steady-state flow measurements confirmed the nematic liquid crystalline phase formation at a lower fraction (φ = 0.24%) for ultra-large GO sheet dispersion than small area graphene oxide dispersion (φ = 0.45%). Further, frequency sweep measurements of ultra-large GO suspension exhibit higher storage and loss moduli than small area graphene oxide dispersion for a particular GO concentration. The study also confirmed the gel-like phase formation at a higher GO fraction (φ > 0.73%), where both storage and loss moduli are nearly independent of frequency. The reported size-dependent viscoelastic properties of GO liquid crystals are very important for the fabrication of GO-based materials for various potential applications.

Semi-flexible star-shaped molecules: conformational analysis of nano-segregated mesogens forming columnar liquid-crystal phases

Abstract The structural prerequisites are investigated, which make star-shaped molecules suitable precursors for the formation of columnar liquid-crystalline phases. Electronic structure calculations on smaller mesogens show that not all conformers exhibit the atomistic structure, the stability against distortion, and additional dipole moments, which favour columnar stacking. For the presently studied compounds with short terminating alkyl chains, the calculations indicate that the steric factor becomes dominant with increasing star size. Thus, the optimised geometric structures were employed to generate a simplified mathematical model of the structures, which accounts only for the steric interaction in the larger stars. With the help of these diagrams, the most common conformers of star-shaped molecules can be derived in a systematic fashion.

Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation

Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation

Liquid crystalline polyurethanes modified by Trisilanolisobutyl-POSS

A series of liquid crystalline polyurethanes based on 4,4′-bis(hydroxyhexoxy)biphenyl moieties and modified by Trisilanolisobutyl-POSS (TRIS-POSS) was synthesized via a polyaddition reaction. ATR-FTIR confirmed introduction of POSS moieties into the macrochain. Formation of liquid crystalline phases along with higher melting and crystallization temperatures due to the addition of the POSS moieties has been observed by Differential Scanning Calorimetry (DSC) and Polarized Optic Microscopy (POM). The influence of the POSS on the improvement of thermal stability and char residue after degradation is also discussed. Influence of the POSS particles on glass transition was found to be relevant for high mesogenic unit load. Morphological investigations by Scanning Electron Microscopy showed different distribution of the POSS nanoparticles for each examined matrix and absence of POSS originated agglomerates which was also confirmed by X-ray diffraction technique. Reinforcement effect of the POSS on mechanical properties was also investigated. Mechanically induced anisotropy was hypothesized to be one of the factor responsible for improved tensile strength at high strain.

Spatially and time-resolved SAXS for monitoring dynamic structural transitions during in situ generation of non-lamellar liquid crystalline phases in biologically relevant media

Formation of high viscous inverse lyotropic liquid crystalline phases in situ upon exposure of low viscous drug-loaded lipid preformulations to synovial fluid provides a promising approach for design of depot formulations for intra-articular drug delivery. Rational formulation design relies on a fundamental understanding of the synovial fluid-mediated dynamic structural transitions occurring at the administration site. At conditions mimicking the in vivo situation, we investigated in real-time such transitions at multiple positions by synchrotron small-angle X-ray scattering (SAXS) combined with an injection-cell. An injectable diclofenac-loaded quaternary preformulation consisting of 72/8/10/10% (w/w) glycerol monooleate/1,2-dioleoyl-glycero-3-phospho-rac-(1-glycerol)/ethanol/water was injected into hyaluronic acid solution or synovial fluid. A fast generation of a coherent drug depot of inverse bicontinuous Im3m and Pn3m cubic phases was observed. Through construction of 2D spatial maps from measurements performed 60 min after injection of the preformulation, it was possible to differentiate liquid crystalline rich- and excess hyaluronic acid solution- or synovial fluid-rich regimes. Synchrotron SAXS findings confirmed that the exposure of the preformulation to the media leads to alterations in structural features in position- and time-dependent manners. Effects of biologically relevant medium composition on the structural features, and implications for development of formulations with sustained drug release properties are highlighted.

Gemini Thermotropic Smectic Liquid Crystals for Two-Dimensional Nanostructured Water-Treatment Membranes.

We have developed a two-dimensional (2D) liquid-crystalline (LC) nanostructured water-treatment membrane showing high virus rejection ability (over 99.99997% for bacteriophage Qβ) and improved water permeation. Polymerizable gemini amphiphiles have been designed and synthesized. They have H-shaped gemini-type structures of thermotropic smectic liquid crystals composed of cationic imidazolium moieties. One of the gemini amphiphiles shows a smectic A phase with an interdigitated bilayer structure. A cross-linked self-standing 2D nanostructured polymer film has been obtained by in situ photopolymerization of the gemini amphiphile in the smectic phase. The length of linkers in gemini amphiphiles affects the formation of LC phases. The 2D nanostructured membrane also showed selective salt rejection.

Synthesis and characterization of liquid crystalline epoxy resins to study the effect of mesogenic length on the physical properties

Two liquid crystalline epoxy (LCE) resins containing different mesogenic lengths were synthesized and cured with two different aromatic diamine curing agents, diaminodiphenylsulfone (DDS) and diaminodiphenylmethane (DDM) to prepare high performance LCE networks. The spectroscopic structures of LCE resins were identified by Fourier transform infrared (FT-IR) spectroscopy, Proton nuclear magnetic resonance (1H-NMR) spectroscopy, mass (MS) spectroscopy, and the formation of nematic and smectic liquid crystalline phase were observed by differential scanning calorimetry (DSC), and polarized optical microscopy (POM). The curing reactions and liquid crystalline textures of the LCE resins were also studied by DSC and POM on the process of curing. The thermal and mechanical properties were investigated for the cured LCE resins with different mesogenic lengths. These results show that the LCE cross-linked networks with long mesogenic group exhibited much higher storage modulus, glass transition temperature, thermal conductivity, thermal stability, and dimensional stability both in the regions of glassy and rubbery states. In addition, both LCE resins have superior thermal and mechanical properties compared to those of the commonly used epoxy resin.

Liquid crystalline behavior and photoluminescence of lanthanide decanoate nanoparticles synthesized by microwave radiation.

Luminescent lanthanide decanoate nanoparticles (LnC10 NPs; Ln = Pr, Nd, Sm, Eu, Gd, Er) with spherical morphology (<100 nm) have been synthesized via a facile microwave (MWV) method using Ln(NO3)3·xH2O, ethanol/water, and decanoic acid. These hybrid nanomaterials adopt a lamellar structure consisting of inorganic Ln3+ layers separated by a decanoate anion bilayer and exhibit liquid crystalline (LC) phases during melting. The particle size, crystalline structure, and LC behavior were characterized using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and powder X-ray diffraction (ambient and heated). Thermal analysis indicated the formation of Smectic A LC phases by LnC10 nanoparticles, with the smaller lanthanides (Ln = Sm, Gd, Er) displaying additional solid intermediate and Smectic C phases. The formation of LC phases by the smaller Ln3+ suggests that these nanoscale materials have vastly different thermal properties than their bulk counterparts, which do not exhibit LC behavior. Photoluminescence spectroscopy revealed the LnC10 NPs to be highly optically active, producing strong visible emissions that corresponded to expected electronic transitions by the various Ln3+ ions. Under long-wave UV irradiation (λ = 365 nm), bright visible luminescence was observed for colloidal suspensions of Nd, Sm, Eu, Gd, and ErC10 NPs. To the best of the authors' knowledge, this is the first reported synthesis of nanoscale metal alkanoates, the first report of liquid crystalline behavior by any decanoate of lanthanides smaller than Nd, and the first observation of strong visible luminescence by non-vitrified lanthanide alkanoates.

Internal liquid crystal structures in nanocarriers containing drug hydrophobic ion pairs dictate drug release

HypothesisHydrophobic ion pairing (HIP), a solubility engineering technique in which ionic hydrophilic molecules are paired with a hydrophobic counterion, is an attractive strategy for encapsulating ionic water-soluble species into nanocarriers (NCs). Drug release from NCs containing HIP complexes is sensitive to ionic strength, pH, and drug:counterion charge ratio, but the exact mechanism for this was unknown, as was the underlying microstructure inside the NCs. We hypothesize that HIP complexes arrange into liquid crystalline structures in NC cores and that these structures are responsible for salt- and pH-dependent release. ExperimentA model hydrophobic ion pair from the cationic antimicrobial peptide polymyxin B sulfate and the anionic counterion sodium oleate is encapsulated into ~100 nm NCs formed using Flash NanoPrecipitation (FNP) and stabilized with an amphiphilic diblock copolymer, poly(caprolactone)-b-poly(ethylene glycol). Internal structures are observed using synchrotron small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) following NC formulation and are found to vary with polymyxin:oleate charge ratio. In vitro drug release is also measured with changes in pH and two charge ratio. FindingsFor a formulation containing a four-fold charge excess of oleate relative to polymyxin, internal structures rearranged from a lamellar phase into an inverse hexagonal phase. The hexagonal phase formation corresponds to a greatly reduced rate of polymyxin release, suggesting that the polymyxin was incorporated into the center of hexagonally-packed rods. When release tests were repeated using phosphate-buffered saline (PBS) at pH 2.0 to ensure protonation of the oleic acid, all internal structures were eliminated and release occurs much faster than at neutral pH, regardless of charge ratio. These findings shed light on the mechanism behind stimulus-responsive drug release from systems containing hydrophobic ion pairs and enable the rational design of controlled-release formulations by manipulating the formation and dynamics of liquid crystalline phases inside NCs.

Thermotropic Liquid Crystalline Polyesters Using Aromatic Rigid Diols, Unsaturated Fumaric Acid and Flexible Sebacic Acid

In the present study, seven different series of thermotropic liquid crystalline polyesters (TLCPs) containing unsaturated fumaroyl chloride and flexible sebacoyl chloride were synthesized using the interfacial polymerization methodology. Homopolyesters prepared with saturated flexible spacer such as sebacoyl chloride were mesomorphic whereas homopolyesters synthesized using unsaturated aliphatic spacer such as fumaroyl chloride that was non-mesomorphic. Aromatic diad and triad based mesogenic diols were selected as rigid moiety for liquid crystalline phase formation. Within each series, copolyesters were synthesized by varying relative mole ratio of the above two aliphatic diacid chlorides. Most of the liquid crystalline polyesters showed solubility in phenol:tetrachloroethane (60:40) at 40 ᵒC.

The impact of various azole antifungals on the liquid crystalline ordering in itraconazole

Abstract In this paper, thermal and structural properties, as well as molecular dynamics of co-amorphous binary mixtures composed of itraconazole (ITZ) and four other active pharmaceutical ingredients (APIs) with antifungal activity (posaconazole (POS), ketoconazole (KET), fluconazole (FLU), and voriconazole (VOR)), have been investigated. Calorimetric measurements indicated that with increasing concentration of each excipient (EXC), the glass transition temperature and phase transition temperatures, related to the formation of nematic and smectic order, are affected in the binary systems. Comprehensive analysis of the enthalpy of isotropic-nematic transition and the temperature dependence of the order parameter, calculated from infrared data for selected mixtures, supported by the results of X-ray diffraction , enabled us to confirm the suppression of liquid crystalline (LC) ordering in ITZ by KET, FLU, and VOR. On the other hand, ITZ enforced the nematic-like molecular arrangement of POS. Further dielectric measurements revealed that the type of EXC and its content in the mixture have no impact on the ratio of α- and δ-relaxation times (τα and τδ, respectively) in ITZ. Moreover, it was shown that δ-process is more sensitive to the isotropic-nematic phase transition than the α-one, and the formation of the nematic phase in this API occurs at different τα and τδ, dependently on the type of EXC and its concentration in the mixture. Summarizing, the results of our studies are much different with respect to those reported previously by Kozyra et al. [Mol. Pharm. 15 (2018) 5192–5206] and by some of us [Kaminska et al. Eur. J. Pharm. Biopharm. 88 (2014) 1094–1104] for ITZ mixed with various polymers and acetylated maltose, respectively. This finding clearly indicates that there is a different impact of the low and high molecular weight excipients on the ability in the formation of LC phases in ITZ, which may have important implications for the further development of the formulations of this pharmaceutical.

Luminescent Metallacycle-Cored Liquid Crystals Induced by Metal Coordination.

Two rhomboidal metallacycles based on metal-coordination-driven self-assembly are presented. Because metal-coordination interactions restrict the rotation of phenyl groups on tetraphenylethene units, these metallacycles were emissive both in solution and in solid state, and their aggregation-induced emission properties were well-retained. Moreover, the rhomboidal metallacyclic structures offer a platform for intermolecular packing beneficial for the formation of liquid crystalline phases. Therefore, although neither of building blocks shows mesogenic properties, both thermotropic and lyotropic (in DMF) mesophases were observed in one of metallacycles, indicating that mesophases could be induced by metal-coordination interactions. This study not only reveals the mechanism for the formation of cavity-cored liquid crystals, but also provides a convenient approach to preparing supramolecular luminescent liquid crystals, which will serve as good candidates for chemo sensors and liquid crystal displays.