Lyotropic Liquid Crystalline Phases Research Articles

Investigations of the Alignment Process of PBPMLG: 2H NMR Analysis Reveals a Thermoresponsive 90° Flip of the Polymer

AbstractThe application of anisotropic parameters in NMR‐spectroscopy enables the acquisition of spatial and angular information, complementary to those from conventional isotropic NMR‐measurements. The use of alignment media is a well‐established method for inducing anisotropy. PBPMLG is a recently discovered polyglutamate‐based alignment medium, exhibiting thermoresponsive behavior in the lyotropic liquid crystalline (LLC) phase, thus offering potential for deeper understanding of the alignment process. We present one approach for investigating the thermoresponsive behavior by synthesizing specifically deuterated PBPMLG‐isotopologues and their subsequent analyses using 2H NMR‐spectroscopy. It was possible to relate the observed thermoresponsive behavior to a flip of the polymer with respect to the external magnetic field—an effect never observed before in glutamate‐based polymeric alignment media. Furthermore, a solvent‐induced temperature dependent gelation was verified in THF, which might provide yet another opportunity to manipulate the properties of this alignment medium in the future.

Investigations of the Alignment Process of PBPMLG: 2 H NMR Analysis Reveals a Thermoresponsive 90° Flip of the Polymer.

The application of anisotropic parameters in NMR‐spectroscopy enables the acquisition of spatial and angular information, complementary to those from conventional isotropic NMR‐measurements. The use of alignment media is a well‐established method for inducing anisotropy. PBPMLG is a recently discovered polyglutamate‐based alignment medium, exhibiting thermoresponsive behavior in the lyotropic liquid crystalline (LLC) phase, thus offering potential for deeper understanding of the alignment process. We present one approach for investigating the thermoresponsive behavior by synthesizing specifically deuterated PBPMLG‐isotopologues and their subsequent analyses using 2H NMR‐spectroscopy. It was possible to relate the observed thermoresponsive behavior to a flip of the polymer with respect to the external magnetic field—an effect never observed before in glutamate‐based polymeric alignment media. Furthermore, a solvent‐induced temperature dependent gelation was verified in THF, which might provide yet another opportunity to manipulate the properties of this alignment medium in the future.

Preparation and structural characterization of shear-aligned films in a high proton conductive alkyl-sulfonated polyimide with lyotropic liquid crystallinity

Molecular-organized structures of polymer electrolytes have been extensively studied in recent years. Recently, we demonstrated that alkyl-sulfonated polyimide (ASPI) forms a lyotropic lamellar liquid crystalline (LC) phase under humid conditions and exhibits a high proton conductivity of 10−1 S cm−1 in the in-plane lamella direction at 95% relative humidity. In this work, we conducted precise structural evaluations of the lyotropic LC ASPI for in-plane aligned films prepared by a bar-coating method with a concentrated solution. The ASPI concentrated solution exhibited a birefringent feature and lyotropic LC properties. Humidity-controlled in situ polarized infrared spectroscopy confirmed the in-plane anisotropic structure of the aligned film with clear dichroism, and the dichroism did not change under humidification. Humidity-controlled in situ grazing-incidence X-ray scattering measurement revealed the hierarchical LC structure with main-chain smectic ordering in the lyotropic lamella structure of the shear aligned ASPI film.

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.

Geometric features in lyotropic liquid crystalline phase transitions observed in aqueous surfactant systems

Lyotropic liquid crystalline phases are widely known to be formed in aqueous surfactant mixtures. Although the phase behavior of several surfactants has been elucidated in the past years, a striking absence of detailed discussion on how molecular geometric parameters vary as different liquid crystals are formed is consistently seen in literature. The current work aimed to partially fill this gap, by determining how several structural parameters changed in a variety of phase transitions previously observed in aqueous surfactant binary and ternary mixtures. The main findings reveal that the cell parameter dimensions are strongly correlated with the packing fraction of small aggregates in each phase; the folding and interpenetration of surfactant hydrocarbon chains are most likely to happen in phases with lower curvature, and can greatly affect other structural parameters; added components can alter the aqueous surfactant phase behavior at different extents; and highly ordered phases are favored by a substantial decrease in the cross-sectional areas per surfactant; among others. The obtained results enable important knowledge on lyotropic liquid crystal formation, in addition to providing detailed information on how to control and obtain such phases, thus prospecting new insights in areas where they are highly desired.

Metastable and stable phase diagrams and thermodynamic properties of the cetyltrimethylammonium bromide (CTAB)/water binary system

The thermodynamic properties of the cationic surfactant cetyltrimethylammonium bromide (CTAB)/water system were investigated using differential scanning calorimetry (235–395 K) and adiabatic calorimetry (78–320 K), and the stable phase diagram was established, in which the locations of phase boundaries were precisely determined. The micellar phase and the lyotropic liquid crystalline (LC) phases were found to transform into a metastable gel phase via rapid cooling, and a metastable phase diagram was also constructed. The hexagonal LC phase was found to consist of two types of phases with different thermodynamic characteristics. The transitions from the separated two-phase “CTAB crystal + solution” to the micellar and LC phases were also investigated, and it was found that the transition occurs in a two-step manner, wherein the transitions at lower temperatures depended on the thermal history. The enthalpy of fusion of the ice that coexisted with the CTAB crystal did not provide any evidence for the CTAB crystal being hydrated by non-freezing water.

Bioimaging Applications of Non-Lamellar Liquid Crystalline Nanoparticles.

Self-assembling processes of amphiphilic lipids in water give rise to complex architectures known as lyotropic liquid crystalline (LLC) phases. Particularly, bicontinuous cubic and hexagonal LLC phases can be dispersed in water forming colloidal nanoparticles respectively known as cubosomes and hexosomes. These non-lamellar LLC dispersions are of particular interest for pharmaceutical and biomedical applications as they are potentially non-toxic, chemically stable, and biocompatible, also allowing encapsulation of large amounts of drugs. Furthermore, conjugation of specific moieties enables their targeting, increasing therapeutic efficacies and reducing side effects by avoiding exposure of healthy tissues. In addition, as they can be easy loaded or functionalized with both hydrophobic and hydrophilic imaging probes, cubosomes and hexosomes can be used for the engineering of multifunctional/theranostic nanoplatforms. This review outlines recent advances in the applications of cubosomes and hexosomes for in vitro and in vivo bioimaging.

Electron transfer studies of a conventional redox probe in human sweat and saliva bio-mimicking conditions

Modern day hospital treatments aim at developing electrochemical biosensors for early diagnosis of diseases using unconventional human bio-fluids like sweat and saliva by monitoring the electron transfer reactions of target analytes. Such kinds of health care diagnostics primarily avoid the usage of human blood and urine samples. In this context, here we have investigated the electron transfer reaction of a well-known and commonly used redox probe namely, potassium ferro/ferri cyanide by employing artificially simulated bio-mimics of human sweat and saliva as unconventional electrolytes. Typically, electron transfer characteristics of the redox couple, [Fe(CN)6]3−/4− are investigated using electrochemical techniques like cyclic voltammetry and electrochemical impedance spectroscopy. Many different kinetic parameters are determined and compared with the conventional system. In addition, such electron transfer reactions have also been studied using a lyotropic liquid crystalline phase comprising of Triton X-100 and water in which the aqueous phase is replaced with either human sweat or saliva bio-mimics. From these studies, we find out the electron transfer reaction of [Fe(CN)6]3−/4− redox couple is completely diffusion controlled on both Au and Pt disc shaped electrodes in presence of sweat and saliva bio-mimic solutions. Moreover, the reaction is partially blocked by the presence of lyotropic liquid crystalline phase consisting of sweat and saliva bio-mimics indicating the predominant charge transfer controlled process for the redox probe. However, the rate constant values associated with the electron transfer reaction are drastically reduced in presence of liquid crystalline phase. These studies are essentially carried out to assess the effect of sweat and saliva on the electrochemistry of Fe2+/3+ redox couple.

Phase diagrams and microstructures of aqueous short alkyl chain polyethylene glycol ether carboxylate and carboxylic acid triblock surfactant solutions

HypothesisThe surfactant C8EO8CH2COOH (Akypo LF2) and its salts have a small hydrophobic and a significantly longer hydrophilic part. As a consequence, there must be a significant steric constraint, once these surfactant molecules form micelles. In addition, the partially charged headgroups should bring some additional fine-tuning via electrostatic interactions to this “essentially non-ionic” surfactant. ExperimentsPhase diagrams of binary mixtures of water and C8EO8CH2COOH are established over large concentration and temperature ranges, also at different pHs and in the presence of sodium and calcium ions. Surface tensions and osmotic pressures are measured to understand the systems. To evaluate the microstructures, also Dynamic Light Scattering and Small-Angle X-ray Scattering are performed. FindingsApart from the formation of coacervates at very low surfactant concentrations, spherical micelles persist over the whole concentration and temperature range and do not change in size and shape. At very high surfactant concentrations, above 60% by weight, where the headgroups are no longer fully hydrated, the standard core-shell structure of micelles vanishes and highly stabilized aggregates of 8–26 octyl chains are suspended in interdigitated polyoxyethylene layers and form an “osmotic brush”. When the acid is partially transformed to a sodium salt, the repulsion between the micelles increases, whereas bridging between micelles prevails, when the counterions are calcium cations. Remarkably, the negative charges of the headgroups are randomly distributed in the hydrophilic ethylene oxide shell. Altogether, a phase diagram without lyotropic liquid crystalline phases and an extreme shift of the cloud-point in temperature and composition is found, similar to the phase diagram of C8EO8OH already known in literature. The phase properties can be explained by the curvature and packing constraints together with the Lindemann rule applied to short hydrocarbon chains.

Glycolipid Biosurfactants, Mannosylerythritol Lipids: Distinctive Interfacial Properties and Applications in Cosmetic and Personal Care Products.

Biosurfactants produced by a variety of microorganisms show attractive properties (e.g., higher surface activity and biodegradability, lower toxicity, and environmental compatibility) compared to chemically synthesized counterparts. The numerous advantages of biosurfactants have prompted their application to not only the food, cosmetic, and pharmaceutical industries, but agriculture and environmental protection disciplines as well. Among different types of biosurfactants, glycolipids are the most practically useful, due to their high product titers from renewable resources and versatile interfacial and biochemical properties. Mannosylerythritol lipids (MELs) are characteristic glycolipid biosurfactants that are produced by different yeast strains of the genus Pseudozyma. MELs exhibit different lyotropic liquid crystalline phases, such as sponge (L3), reverse bicontinuous cubic (V2), or lamellar (Lα) phases; and they have high levels of surface activity at very low concentrations. MELs also show excellent moisturizing effects on human skin and hair, with comparable performance to natural ceramides. Today, MELs are commercially produced by a Japanese company and their use is rapidly expanding around the world. In this review, we will briefly describe the current R&D status of glycolipid biosurfactants, with a focus on the interfacial properties of MELs and their applications in cosmetic and personal care products.

Lyotropic liquid crystalline phases of anisotropic nanoparticles of organic-inorganic metal halide perovskites: photoluminescence from self-assembled ordered microstructures of semiconductors.

A simple method (which could be completed within 60 minutes at 298 K) was developed to transform layered organic-inorganic metal halide perovskites into colloidal lyotropic liquid crystalline dispersions with microscopic structural orderliness as well as semiconducting properties and photoluminescence. Experimentally, hexagonal-shaped mesogenic nanoplatelets of two-dimensional lead iodide perovskites (R-NH3)2PbI4 were synthesized by antisolvent-induced rapid microcrystallization and stabilized by surfactants, and self-assembled into discotic-nematic phases with optical anisotropy and greenish-blue fluorescence. Combining the stimuli-responsive, light-interactive, and reconfigurable ordered structures of liquid crystals with the adjustable semiconductivity of hybrid perovskites, these photoluminescent soft anisotropic materials may be used for polarized light emission or detection.

The Effects of Size and Shape Dispersity on the Phase Behavior of Nanomesogen Lyotropic Liquid Crystals

Self-assembly of anisotropic nanomaterials into fluids is a key step in producing bulk, solid materials with controlled architecture and properties. In particular, the ordering of anisotropic nanomaterials in lyotropic liquid crystalline phases facilitates the production of films, fibers, and devices with anisotropic mechanical, thermal, electrical, and photonic properties. While often considered a new area of research, experimental and theoretical studies of nanoscale mesogens date back to the 1920s. Through modern computational, synthesis, and characterization tools, there are new opportunities to design liquid crystalline phases to achieve complex architectures and enable new applications in opto-electronics, multifunctional textiles, and conductive films. This review article provides a brief review of the liquid crystal phase behavior of one dimensional nanocylinders and two dimensional nanoplatelets, a discussion of investigations on the effects of size and shape dispersity on phase behavior, and outlook for exploiting size and shape dispersity in designing materials with controlled architectures.

Mapping the Impact of a Polar Aprotic Solvent on the Microstructure and Dynamic Phase Transition in Glycerol Monooleate/Oleic Acid Systems.

The impact of incorporating a polar aprotic solvent, dimethyl sulfoxide (DMSO), in glycerol monooleate/oleic acid systems was evaluated briefly to map its influence on the gel microstructure and dynamic phase transition in controlling the performance of a polyene antifungal drug delivery system. An in situ gelling fluid precursor system (IGFPS) exhibiting inverse lyotropic liquid crystalline phases was developed by simple solution add-mixture method. Polarized light microscopy, small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and oscillatory rheological assessments were performed to ascertain microstructural modulations. The developed system was examined for minimum gelling volume, gelling time, swelling behavior, mucoadhesion, in vitro antifungal activity, and in vitro drug release. The SAXS study identifies the coexistence of Im3m cubic phase with HCP P63/mmc hexagonal structures. The SAXS and DSC data highlight DMSO's unique ability to work both as a kosmotropic or chaotropic solvent and to be a function of its concentration. The in vitro antifungal test results indicate the concentration of DMSO to be a controlling factor in drug release and diffusion. The in vitro drug release kinetic studies reveal that most of the gel samples follow the matrix model and anomalous type release as implied by Peppas model. Finally, the antifungal IGFPS formulated was found to have the required low viscosity, responsive sol-gel phase transition, appreciative mechanical properties, and desirable antifungal effect with sustained drug release performance.

Poly-γ-S-perillyl-l-glutamate and Poly-γ-S-perillyl-d-glutamate: Diastereomeric Alignment Media Used for the Investigation of the Alignment Process.

Residual dipolar couplings (RDCs) offer additional information for structure elucidation by NMR spectroscopy. They are measured in anisotropic media, such as lyotropic liquid crystalline phases of polypeptides. Today, some suitable polypeptides are known. Nevertheless, structural influences of these polypeptides on the alignment properties are not really understood. Thus, which influence a chiral side chain has on enantiodiscrimination and whether we can improve the enantiodifferentiation significantly by adding an additional chiral center in the side chain are questions of interest. Therefore, new diastereomeric polypeptide‐based alignment media with an additional chiral center in the side chain derived from perillyl alcohol were synthesized and their properties were investigated (secondary structure, liquid crystallinity, etc.). The enantiomers of isopinocampheol and β‐pinene were used as model analytes for the study of enantiodiscrimination. Additionally, the usage of 1H–1H‐RDCs to improve the alignment tensor quality is demonstrated.

Polymer Coated Semiconducting Nanoparticles for Hybrid Materials

This paper reviews synthetic concepts for the functionalization of various inorganic nanoparticles with a shell consisting of organic polymers and possible applications of the resulting hybrid materials. A polymer coating can make inorganic nanoparticles soluble in many solvents as individual particles and not only do low molar mass solvents become suitable, but also polymers as a solid matrix. In the case of shape anisotropic particles (e.g., rods) a spontaneous self-organization (parallel orientation) of the nanoparticles can be achieved, because of the formation of lyotropic liquid crystalline phases. They offer the possibility to orient the shape of anisotropic nanoparticles macroscopically in external electric fields. At least, such hybrid materials allow semiconducting inorganic nanoparticles to be dispersed in functional polymer matrices, like films of semiconducting polymers. Thereby, the inorganic nanoparticles can be electrically connected and addressed by the polymer matrix. This allows LEDs to be prepared with highly fluorescent inorganic nanoparticles (quantum dots) as chromophores. Recent works have aimed to further improve these fascinating light emitting materials.

Aqueous Lyotropic Mesophase Behavior of Gemini Dicarboxylate Surfactants Swollen with n-Decane.

We report detailed small-angle X-ray scattering (SAXS) studies of the impact of variable n-decane loadings on the lyotropic liquid crystalline (LLC) phase behaviors of homologous bis(tetramethylammonium) gemini didecanoate surfactants TMA-7x, which derive from dimerizing decanoic acid through its α-carbon with hydrocarbyl linkers -(CH2)x- where x = 3, 4, 5, and 6. TMA-7x amphiphiles with x = 3 or 5 exhibit a strong propensity to form normal double gyroid (G) LLC network mesophases over wide surfactant hydration ranges, as compared to homologues with x = 4 or 6. On swelling aqueous TMA-7x LLC mesophases with up to 35 wt % n-decane, we demonstrate that odd-carbon linked surfactants (x = 3 or 5) form G and normal double diamond (D) phases over wide water concentration windows with T = 22-100 °C. Complementary studies of decane-swollen TMA-7x (x = 4 or 6) aqueous LLCs instead demonstrate significantly diminished network phase stability, in favor of hexagonally-packed cylinder phases and a zoo of complex quasispherical micelle packings, which include micellar C14 and C15 Laves phases (P63/mmc and Fd3(-)m symmetries, respectively) and high-symmetry hexagonally close packed (HCP) and body-centered cubic (BCC) arrangements. These rich phase behaviors are rationalized in terms of linker length parity-dependent surfactant conformations and the delicate free energy balance that guides the packing of these geometrically anisotropic amphiphiles by minimizing unfavorable water-hydrophobic contacts, maximizing ionic surfactant-headgroup counterion solvation with minimal local variations, and maximizing electrostatic cohesion within these supramolecular assemblies.

Valine derived poly (acetylenes) as versatile chiral lyotropic liquid crystalline alignment media for RDC-based structure elucidations.

Anisotropic samples of lyotropic liquid crystalline (LLC) phases of valine derived polyaryl acetylenes were employed as chiral alignment media for the measurement of residual dipolar couplings (RDCs) of 12 small, chiral, organic molecules. The quadrupolar splitting of the deuterium signal of CDCl3 can be adjusted by temperature and concentration changes from 0 to 350 Hz. The LLC phases showed excellent orienting properties for all analytes bearing various functional groups. The precise extraction of RDCs in the range of up to ±30 Hz from F2-coupled HSQC spectra was possible. Additionally, the chiral environment led to diastereomorphous interactions with the enantiomers of chiral analytes leading to two different sets of RDCs. This differential order effect was particularly pronounced with H-bond donors like alcohols and 2° amines.

Temperature-dependent dielectric dynamics, relaxation, and conductivity behavior of aqueous and nonaqueous lyotropic liquid crystalline phases

ABSTRACT Lyotropic phases are derived from cetyl pyridinium chloride and sodium dodecyl sulfate surfactants via dissolving them in water and glycerol. A significant increase in the dielectric permittivity of lyotropic mixtures has been observed as a function of increasing temperature in all lyotropic phases irrespective of surfactant nature. A single relaxation peak corresponding to the Cole-Cole relaxation process has been observed for all the studied mixtures. Non-Arrhenius variation of the relaxation frequency seen for these lyotropic mixtures represents the Vogel-Fulcher-Tammann (VFT) behavior. An increase in dc conductivity is observed as a function of temperature, which becomes more prominent at a higher temperature > 50°C. Highest dc conductivity of the order of 10−4 S/m noticed for these systems is one of the key findings of this study. Optical studies confirm that aqueous and nonaqueous lyotropic mixtures exhibit a wide optical bandgap ranging from 4.0 to 4.5 eV.

Lipid-based lyotropic liquid crystalline phase transitions as a novel assay platform using birefringence as the visual signal output.

Amphiphilic lipids can often form various lipid-based lyotropic liquid crystalline phases when they are exposed to aqueous environments, which includes the inverse hexagonal (H2), inverse cubic (V2), inverse discontinuous cubic (I2) and lamellar (Lα) phases. Their different interactions with crossed-polarised light make some phases appear bright and some dark, which offers great potential in developing a novel universal assay platform using birefringence as the visual signal output. Here, we have developed a novel strategy for constructing an assay platform using lyotropic liquid crystalline phases as the signal transducer and using changes in their birefringence upon exposure to lipase as the signal output. The hydrolysis of the ester group of glyceryl monooleate (GMO) by lipase induced a phase transition from cubic phase to hexagonal phase and consequently "turned on" the birefringence as the signal output. The change in the intensity of the birefringence depended on both the exposure time and concentration of lipase. The streptavidin-biotin affinity was utilised to demonstrate the potential of the birefringence assay platform, using free biotin as the model analyte, biotinylated lipase and streptavidin-coated magnetic beads in the competitive format. A semi-quantitative assay with a detection limit of 5 μg mL-1 to free biotin as the model analyte was achieved in the visual birefringence mode. This study demonstrated a proof-of-concept lyotropic assay platform with birefringence as the visual signal output that could be deployed as an electronics- and colour-free diagnostic device for a wide range of applications, for example to indicate the presence of toxins in water.

Magnetic field induced uniaxial alignment of the lyotropic liquid-crystalline PMMA-grafted Fe3O4 nanoplates with controllable interparticle interaction.

Magnetite (Fe3O4) nanoplates with a hexagonal platelet shape were synthesized by two steps: hydrothermal synthesis of iron(iii) oxide (α-Fe2O3) nanoplates followed by wet chemical reduction of the α-Fe2O3 nanoplates. Then, poly(methyl methacrylate) (PMMA) chains were grafted onto the surface of the hexagonal Fe3O4 nanoplates (F) via surface-initiated atom transfer radical polymerization (SI-ATRP), which ensures dispersion stability in organic solvents and ionic liquids. After mixing with 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Emim+][NTf2−]), a representative ionic liquid, the resulting PMMA-modified F were found to show good lyotropic liquid-crystalline (LC) behaviour in [Emim+][NTf2−] and to exhibit a fast response to the application of an external magnetic field. Ultrasmall-angle synchrotron X-ray scattering (USAXS) measurements verified that the PMMA chain length, the weight ratio of the ionic liquid and the external magnetic field could significantly influence the interparticle distance (ID) of the PMMA-modified F in [Emim+][NTf2−]. In particular, the lyotropic LC phase could be assigned as a nematic phase with a columnar alignment. In addition, the PMMA-modified F maintained a uniaxially aligned nematic columnar structure along the magnetic field direction. Our study also determined the mechanism for the special alignment of the PMMA-modified F under an external magnetic field by analysing the growth axis, the easy magnetic axes, and the interparticle distance of F. The results suggested that the special alignment of the PMMA-modified F was affected by the interparticle interaction caused by the PMMA long chains on F under the magnetic field. Furthermore, the present study revealed that PMMA-modified F exhibited a new magnetic field responsive behaviour that led not only to the formation of a uniaxial alignment structure but also to control of ID with the help of the PMMA soft corona under the application of a magnetic field. These features could prove to be a promising advance towards novel applications of magnetic nanoparticles (NPs), such as functional magnetic fluids, rewritable magnetic switching devices, and smart magneto-electrochemical nanosensors.