Liquid Crystal Region Research Articles

Liquid Crystal Ordering in Densely Packed Colloidal Suspensions of Highly Anisotropic Monolayer Nanosheets

Monolayer nanosheets of zirconium phosphate in aqueous suspension exhibit short-range repulsion and long-range attraction, producing, at overall volume fractions larger than about half a percent, phase separation into higher-concentration liquid crystal and lower-concentration isotropic regions. At high concentrations, this phase separation takes the form of an emulsion of condensed, liquid-crystalline droplets, which anneal to form lens-shaped tactoids. These tactoids provide an opportunity to study the liquid crystal ordering of inorganic nanosheets in the limit of large shape anisotropy (diameter/thickness~400) and high packing fraction (volume fraction ≳ 70%). The internal liquid crystal structure of the tactoids remains nematic even under conditions that would usually favor ordering into lamellar smectics. Local lamellar ordering is suggested by short-range, smectic-like layer correlations, but a full transition into a smectic phase appears to be inhibited by the nanosheet edges, which act as a perturbative population of dislocation loops in the system of layers. Under conditions of thermal equilibrium, the nanoplates organize positionally to enable bend deformation of the director, a hallmark of the nematic phase and its principal distinction from the smectic, where bend must be expelled.

Preparation and characterisation of liquid crystal elastomer films with selective reflectivity

ABSTRACT In this paper, the liquid crystal elastomer films (A’BG series) have been prepared by grafting polymerisation, using the 4-allyloxybenzoic acid cholesteryl ester (MB) as liquid crystal monomer, dodecane-1,12-diyl bis(undec-10-enoate) (MG) as flexible cross-linker and polymethyl hydrosiloxane (containing 35 Si-H) as the main chain. The A’BG series films are cholesteric liquid crystal elastomer films (LCEs) with a liquid crystal region above 100°C. With the crosslinker content decreasing, A’BG-2 and A’BG-3 display selective reflection in UV region and visible region, respectively. The selective reflection wavelength of A’BG-3 occurs blue shift with the temperature increasing. The glass transition temperatures (Tg) of the A’BG series films are 16.4–40.8°C and A’BG series films display shape memory properties near room temperature. The A’BG series elastomer films have a high thermal stability and the temperatures of the 5% mass loss are above 300°C. The backbone siloxane structures in the A’BG series elastomer films are highly stable, and the -COOChol group is relatively easy to decompose.

Propagation of ultrasound near phase transitions in the liquid crystal working environment of technical devices

The results of measurements of the velocity and absorption coefficient of ultrasound in a nematic phase oriented by a magnetic field are presented. Within the framework of the hydrodynamics of the nematic phase, the coefficients of the bulk and shear viscosity of the nematic phase are calculated. The temperature dependence of the shear viscosity coefficients is exponential. The nature of the sharp increase in the bulk viscosity coefficients with an increase in the temperature of the nematic phase in the region of the phase transition nematic liquid crystal - isotropic phase is analyzed. The analysis of the temperature dependence of the ultrasound velocity in the nematic phase, carried out under the assumption of the existence of two processes responsible for the propagation of ultrasound, allowed us to identify the critical component and calculate the relaxation time of the critical contribution. In the vicinity to the phase transition, the dependence on the temperature of the relaxation time of the critical contribution increases sharply with a divergence index equal to 1.03. The relationship between the critical contribution to the absorption and the speed of ultrasound has been established. An array of data necessary for the calculation of liquid crystal technical devices has been obtained.

Controllable Liquid Crystal Micro Tube Laser

This study demonstrates controllable random lasing emissions in a dye-doped nematic liquid crystal (DDNLC)-infiltrated microcapillary. The emission wavelength of the micro tube laser can be adjusted by changing the focusing position of the pumped pulses on the center or the periphery of the liquid crystal region of the microcapillary. In addition, with doping azo-dyes in the DDNLC of the micro tube laser, optical controllability of the lasing intensity and wavelength can be further achieved. The controllable micro tube laser may find highly widespread photonic applications in multicolor emitting sources, and vibration and UV sensors.

Quantitative analysis of stereoscopic molecular orientations in thermally reactive and heterogeneous noncrystalline thin films via variable-temperature infrared pMAIRS and GI-XRD

The quantitative estimation of stereoscopic molecular orientations in semicrystalline polymer thin films with characteristic heterogeneous structures is essential for the development of advanced film materials. Grazing-incidence X-ray diffraction (GI-XRD) is a powerful technique used to evaluate the orientational order of crystalline lattices; however, it provides the orientational order of only ordered regions (crystal and glassy liquid crystal regions). In contrast, infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) can provide the averaged orientational order of overall regions in a film regardless of sample crystallinity. This paper combines variable-temperature (VT) pMAIRS, static GI-XRD and spectroscopic ellipsometry and reports general insight into the molecular orientation mechanism occurring in polymer films revealed through the precise analysis of the structural evolution of linear poly(amic n-alkyl ester), PAE, with different lengths of n-alkyl chains during thermal curing, which involves solvent evaporation and dehydration imidization reactions to form the corresponding polyimide (PI). This combined method clarified that the PAE and PI thin films had a heterogeneous structure consisting of a glassy liquid-crystalline (ordered) region and a nonoriented amorphous region. Furthermore, imidization proceeded faster in the amorphous region than in the ordered (oriented) region. In addition, anomalies of refractive index and birefringence were found by comparing pMAIRS and spectroscopic ellipsometry, although the effect of the side chain length on the molecular orientation of PI was insignificant. The anomalies indicate that an isotropic void structures were generated by the elimination reaction of the side chains and that the volume fraction of voids increased with increasing side chain length. These results demonstrated that the combination of VT-pMAIRS and GI-XRD is a very powerful tool for the in situ structural analyses of noncrystalline (disordered crystal, glassy liquid crystal, and oriented amorphous) thin-film materials ongoing chemical reactions in their components and is inherently applicable to all kinds of interesting polymeric thin-film materials. Thin film aromatic polyimides were quantitatively analyzed by grazing-incidence X-ray diffraction (GI-XRD), variable-temperature infrared p-polarized multiple-angle resolution spectroscopy (VT-pMAIRS), and spectroscopic ellipsometry (SE) methods. Combining VT-pMAIRS and GI-XRD revealed characteristic heterogeneous structures comprising non-oriented amorphous and oriented liquid-crystalline glass regions. Additionally, SE indicated that the film involved anisotropic-shaped void inducing form-birefringence. Such an excess of birefringence can make it difficult to estimate orientational order using birefringence measurement. This methodology presented here will remarkably contribute to general structural analyses of all intriguing thin-film polymers with characteristic heterogeneity.

Effect of [Zr4+] to [SO2-4] molar ratio on the zirconia phase structure in lamellar liquid crystal of SDS/water/1-decanol ternary system

ABSTRACTPure tetragonal zirconia nanopowder was prepared via lamellar liquid crystal method combined with a thermal sulfated zirconyl chloride hydrosol. The lamellar liquid crystal region in the sodium dodecyl sulfate/1-decanol/water ternary phase diagram was observed by polarizing optical micrographic images. The impact of the molar ratio on the phase and morphology of zirconia was investigated. Results showed that the molar ratio Rs affected the phase structure and morphological characteristic of zirconia particles. Moreover, the morphology was transformed from almost peanut particles to spherical ones, whereas tetragonal phases changed into monoclinic phase with the increase in Rs.

RELEASING OF ACETYL HEXAPEPTIDE-3 USING A LECITHIN BASED LIQUID CRYSTAL SYSTEM

One of the promising areas of application of liquid crystal systems for medicine and cosmetics is the development of matrices for drug delivery. A relatively new technology for this is the use of lecithin-based liquid crystal systems, in which the smallest droplets of the aqueous phase are stabilized not by ordinary emulsifiers, but by a network of bilayers of surfactants, like those that make up the lipid barrier. In this regard, the lecithin / water / propylene glycol /vaseline oil system, which is non-toxic and biodegradable, was obtained and investigated. By finding the minimum interfacial tension of lecithin at the boundary of the water-propylene glycol mixture / mineral oil, the necessary concentrations of the components of the aqueous phase were selected. Phase diagram was received. The liquid crystal region was studied by the method of polarization-optical microscopy. It was determined that in this area the system self-organizes with the formation of a lamellar mesophase. The results of the study of the phase behavior of lyotropic liquid-crystal systems with incorporated substances contribute to an understanding of the processes of their delivery and to solving the problem of release, since the supermolecular structure is destroyed during the phase transition and the active substance is released. In this regard, acetyl hexapeptide-3, which is an analogue of botulinum toxin and widely used in cosmetics and medicines, was introduced into the system, and UV spectra of the peptide were obtained. With the use of the Franz diffusion cell, the release of acetylhexapeptide-3 through a cellophane membrane was investigated. The quantitative characteristics of the introduction of the peptide into the complex were established. Its prolonged action is shown when passing through the membrane. This system can be used as a basis for the transport of peptides into skin cells.

On the Relationships between the Hydrophilic–Lipophilic Balance and the Nanoarchitecture of Nonionic Surfactant Systems

AbstractBuilding links between established parameters for the characterization of surfactant systems is useful not only for the understanding of the underlying phenomena but also for the judicious formulation of products. Herein, we review comprehensively the literature data to find correlations between the hydrophilic–lipophilic balance (HLB) and the molecular packing parameter (CPP) for a variety of nonionic surfactants in water. The interfacial area per surfactant molecule, a fundamental variable to calculate CPP, follows a power law as a function of the number of ethylene oxide (EO) groups in the surfactant. The exponent ranges from 0.3 to 0.7, which may reflect changes in the conformation of the EO chain depending on the nature of the hydrophobic group; there is also apparently a transition toward a collapsed conformation of the EO chains at high surfactant concentrations. CPP is found to change linearly with HLB in the range of data studied, although the parameters of the linear fitting depend on the nature of both hydrophobic and hydrophilic moieties of the surfactant; this would also imply a linear relationship between CPP and the HLB temperature (i.e., Phase Inversion Temperature) according to the Kunieda–Shinoda equation. Analysis of the liquid crystal regions of the surfactant phase diagram at constant temperature indicates that the HLB values required for the morphological phase transitions defined by CPP increase with surfactant concentration. The present report may serve as a contribution to the programmed design of nanoarchitectures in surfactant systems.

Effect of 1-hexanol on the phase behavior of SDS/CTAB/NaBr/H2O system

The influence of 1-hexanol on the phase behavior of sodium dodecyl sulfate (SDS)/cetyltrimethyl ammonium bromide (CTAB)/NaBr/H2O system has been systematically investigated in this paper. The results showed 1-hexanol effectively dissolved the precipitate formed by the CTAB and SDS surfactants, while liquid crystal (LC) and aqueous two phase system (ATPS) were formed in a wider range. When the molar ratio of 1-hexanol to surfactant is higher than 1, the precipitation in the system disappeared completely and was transformed into ATPS and LC, indicating that alcohol inserted at least evenly between every two surfactant molecules and hence effectively weakened the electrostatic interaction between the anionic and cationic surfactants and limited the formation of precipitation. Polarizing microscope (POM) with crossed polarizers was employed to investigate the textures of liquid crystals. It was shown that the existence of lamellar LC was confirmed by “Maltese crosses” textures. Additionally, we showed that the thermal stability of LC was promising. The ATPS and LC regions remained stable and changed slightly when the temperature was increased from 40 to 70 °C. The results indicated that ATPS and LC of the system were quiet resistant to temperature with the addition of 1-hexanol.

Observation of applied voltage response of dye-doped liquid crystal by optical measurement of real and imaginary parts of complex refractive index

The behavior of liquid crystal (LC) molecules and dye molecules in a dye-doped liquid crystal (DDLC) under a voltage application condition was quantitatively investigated. To observe the reorientation of these molecules, the real and imaginary parts of the complex refractive index were simultaneously and individually measured using an optical interferometer. The obtained results indicate that the alignment of dye molecules doped in DDLC occurs following the electrically responding LC molecules, near the Freedericksz transition region of LC.

Direct measurement of the propagation of the phase-transition region of liquid crystals

Many types of active matter, such as biological cells, have liquid-crystalline membranes, which are soft and flexible in their interactions with their surroundings and sometimes allow molecular-structural or -orientational changes to extend for long distances, owing to long-range molecular interactions. Despite the technological and fundamental importance of these long-range changes, there is no good physical property with which to express them for the liquid crystal. Here, we show direct measurements of the propagation of structural or orientational changes due to long-range molecular interactions in liquid crystals. We induced a patterned phase transition in a liquid crystal via illumination with a fringe pattern and observed the propagation of the phase-transition region. We determined that the propagation occurred in a ballistic manner with a velocity of 80–110 m/s and that two types of propagation—side-by-side and head-to-tail molecular interactions—were found.

Interaction between organized assemblies of amphiphilic molecules and biological active molecules

Organized assemblies formed by amphiphilic molecules have various structures, including micelles, microemulsions, vesicles, lamellar liquid crystals, and hydrogel. Due to the similarity between the basic structure of the life system and molecular organized assemblies, these organized assemblies are of much importance as a convenient model for studying the biomacromolecules such as protein and phospholipids bilayer and also of great significance from the viewpoint of various promising practical applications. Therefore, it is of great theoretical and practical significance to study the interaction between organized assemblies of amphiphilic molecules and biological active molecules. In recent years, we have carried out a series of work in this area. We designed and synthesized some amino acid, glucoside and ionic liquid based functional green surfactants. These new surfactants can self-assemble into organized assemblies having various structures, such as micelles, vesicles, lamellar liquid crystals, and hydrogel. The mutual transformation among these different molecular ordered assemblies can be regulated by the molecular structure of surfactants and environmental factors. The molecular self-assembly of surfactants based on noncovalent interactions, such as hydrogen-bond, static electricity, solvophobic interaction and π-π stacking, etc, provides a powerful tool for the creation of well-defined structures in certain dimensions, and the transform among these organized assemblies. Furthermore, the interaction relationship between amphiphilic molecules and biological active molecules has been revealed by studying their thermodynamic and kinetic characteristics. Methemoglobin and GDA/ n -C5H11OH/H2O assemblies can affect their structures and properties, and the change in behavior is dependent on the content of methemoglobin and the composition and structure of the GDA/ n -C5H11OH/H2O system. The existence of methemoglobin reduces the hexagonal liquid crystal region, while the lamellar liquid crystal region is little changed in the presence of methemoglobin. The addition of amino acid does not change the structure of the microemulsions ultimately, but results in the redistribution of surfactants between the upper and lower phases. Furthermore, the distribution of amino acid between the phases can be adjusted by changing the total surfactant content. The exact location of the drugs depends on both the micellar structure and the molecular structure. The different locations of drugs in the micelle influence the structure-function of the drugs. Flavonoids show selective dimerization with the micelle structure change. It is always in the form of a dimer in spherical micelles, while it is in the form of a monomer in the rodlike micelles. The antihydrolysis and antioxidation activity of drug molecules can be modulated by changing and adjusting the microstructure of the molecular ordered assemblies. The clearance of hydroxyl radicals by morin and the protection of human serum albumin against hydroxyl radical induced damage by morin have been reduced in the Triton X-100 micelles. This dynamic process of puerarin’s localization in micelles causes the acid–base equilibrium of puerarin to move to the deprotonation reaction, enhancing the interaction between puerarin and surfactants, and promoting the formation of the puerarin–surfactant associate. With the changes of membrane hydrophobicity the effect of puerarin on membrane-water interfaces enhances and puerarin can locate more internally in the region of membranes, favoring the deprotonation of puerarin. Based on this, the relationship between the structure-function of bioactive molecules and the microenvironment is clarified from molecular level. This provides important theory and application basis for life sciences, medicine, pharmacy and other related fields.

The phase behaviors of cationic and anionic aqueous mixtures and the usage as templates for synthesis of mesoporous materials

Liquid crystals formed in aqueous mixtures of cationic and anionic surfactants were used as structure- directing templates for preparation of mesoporous silicas. For this purpose, micellar particle sizes and liquid crystal regions in the mixed system containing cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were investigated by Melvin laser particle size analyzer and polarizers, respectively. The formation of large organized assemblies was closely related to both the total surfactant concentrations and mixing ratios. Micelles formed at low total concentration while liquid crystals formed at high total concentration. The mixtures of CTAB and SDS favored the formations of large organized assemblies when the molar fraction of CTAB was 0.30 or 0.70. Using tetraethoxysilane as precursor and liquid crystals as templates, mesoporous silicas were prepared at different total concentrations of surfactants when molar fraction of CTAB was fixed at 0.70. Transmission electron microscopy results revealed that ordered mesoporous silicas with lamellar pore channels were prepared. Nitrogen adsorption-desorption determinations showed that these materials exhibited a pore size about 4.5 nm. In addition, the surface areas increased significantly with the increase of total surfactant concentrations. This work provided a simple and effective approach to synthesize lamellar mesoporous silicas.

Electrically controlled spatial-polarization switch based on patterned photoalignment of nematic liquid crystals.

A switching scheme for two orthogonal modes of laser radiation that is based on the total internal reflection effect realized at the interface of two liquid crystal regions with orthogonal director orientations is proposed. To create the photorefractive interface within the bulk of a liquid crystal, an original technique based on self-alignment of azo dye photoalignment and absorbing electrode patterns has been developed. Spatial separation of the orthogonally polarized light beams and their switching (when the positions of reflected and transmitted light beams are switched) due to the voltage applied has been experimentally realized.

Phase behavior and phase structure of 1:1 salt-free catanionic surfactant dodecyltrimethylammonium decanoate

The salt-free catanionic surfactant dodecyltrimethylammonium decanoate (DTAD) was synthesized by a novel method. Phase behavior and phase structure of DTAD with water at full concentration range were studied at 20–45°C, using differential scanning calorimetry (DSC), freeze-fracture transmission electron microscopy (FF-TEM), polarization microscopy, and small-angle X-ray diffraction (XRD) techniques. The DTAD–water system formed a large aqueous multi-phase region, a large lamellar liquid crystal (Lα phase) region, and a hydrated crystal phase. The densely packed vesicles and the lamellar structure induced the formation of aqueous multi-phase region. With increasing temperature, the multi-phase region and the Lα phase region reduced, and the isotropic solution phase (L1 phase) appeared.

Liquid crystalline phase in xanthan gum (XG)/H2O/H3PO3 and XG/H2O/H3PO4 tertiary systems: a thermal and rheological study

This study investigates the difference in phase transition and rheological behavior between xanthan gum (XG)/H2O/H3PO3 (XWP3) and XG/H2O/H3PO4 (XWP4) tertiary systems using polarized optical microscopy, Fourier transform infrared spectroscopy, light transmission detection, and rheometry. The results show that the LC (liquid crystal) phase formation in the XWP4 system was more strongly suppressed than that in the XWP3 system because the former exhibited stronger interactions between acid and XG molecules. With respect to the transition from LC to I (isotropic) phase at high temperature, the transition time of the XWP4 system was found to be much shorter than that of the XWP3 system. The transition time, also called the relaxation time, was measured by observing the annealing time and fitted using the VFT expression. The activation energies E for this transition in XWP4 and XWP3 systems are 3.0 and 4.7 kJ/mole, respectively, indicating that the XWP3 system exhibits stronger intermolecular attraction and is more sensitive to variation in temperature. In the rheological tests, as the temperature of the XWP4 system increased from 25 to 95 °C, the viscosity in the transitional region declined consistently, while in the XWP3 system, the decline proceeded through three stages owing to the shifting tautomers of the H3PO3. In the LC region, the viscosity normally fell as the shear rate or temperature increased but increased with the heating rate or XG concentration. Most interestingly, all of the results herein demonstrated that the viscosity of the XG solution in the LC region followed a power law with an index of roughly 0.08, which was found to be independent of the type of acid, concentration of acid, and XG concentration.

Phase Behavior and Rheological Properties of Concentrated Lecithin Aqueous Solutions with Additives

The phase behavior and rheological properties of the concentrated lecithin aqueous solutions were investigated at 37°C. When adding Isopropyl myristate (IPM) to lecithin solutions, besides an anisotropic liquid crystal (LC) phase, an isotropic liquid (L2) region and an isotropic viscous (I) phase are found. By continuously adding Brij 97, the LC region shifts towards higher water content and the L2 region is extended to the area of lower IPM concentration, meanwhile the I phase disappears. By analyzing the shear rate (ηγ=0.1) and yield stress (σ0), adding IPM to lecithin solutions increases the values of ηγ=0.1 and σ0, and after further adding Brij 97, the ηγ=0.1 and σ0 decrease dramatically. Notably, different from the lecithin/DDAB/water system studied by Youssry and Montalvo, in lecithin/Brij 97/IPM/H2O system, at the relatively higher water content area of the LC phase, the water content has little effect on the critical stress. It is also found that the change of dynamic storage modulus (G′) is similar with that of ηγ=0.1 and σ0 parameters when adding IPM and Brij 97. Maxwell model fitting results show that in the LC phase, the relaxation of the water molecule is prolonged by adding IPM and Brij 97 to lecithin solutions.

Synthesis and characterisation of reactive liquid crystals containing an azo group

A new series of liquid crystal (LC) monomers – not only contain a double bond but also contain an azo group – were designed and synthesised. The length of side groups in the LC monomers containing azobenzene ester varied from 1 to 2 methylene units, and the length of the substituted groups in the main chain varied from 1 to 3 methylene units. The molecular structures of the intermediates and target compounds were confirmed by Fourier transform infrared, ultraviolet and visible spectrum and nuclear magnetic resonance (NMR) spectroscopy. The thermal phase behaviour of the LC monomers was investigated by polar optical microscopy coupled with hot stage and differential scanning calorimetry (DSC). In this paper, the effect on the LC zone with the substituents were investigated, and with the increased methylene of main chain, the melting point and the phase transition temperature of the substance will be lowered and LC regions will be narrower.

Lecithin based lamellar liquid crystals as a physiologically acceptable dermal delivery system for ascorbyl palmitate

Liquid crystalline systems with a lamellar structure have been extensively studied as dermal delivery systems. Ascorbyl palmitate (AP) is one of the most studied and used ascorbic acid derivatives and is employed as an antioxidant to prevent skin aging. The aim of this study was to develop and characterize skin-compliant dermal delivery systems with a liquid crystalline structure for AP. First, a pseudoternary phase diagram was constructed using Tween 80/lecithin/isopropyl myristate/water at a Tween 80/lecithin mass ratio of 1/1, and the region of lamellar liquid crystals was identified. Second, selected unloaded and AP-loaded lamellar liquid crystal systems were physicochemically characterized with polarizing optical microscopy, small-angle X-ray scattering, differential scanning calorimetry, and rheology techniques. The interlayer spacing and rheological parameters differ regarding quantitative composition, whereas the microstructure of the lamellar phase was affected by the AP incorporation, resulting either in additional micellar structures (at 25 and 32°C) or being completely destroyed at higher temperature (37°C). After this, the study was oriented towards in vitro cytotoxicity evaluation of lamellar liquid crystal systems on a keratinocyte cell line. The results suggest that the lamellar liquid crystals that were developed could be used as a physiologically acceptable dermal delivery system.

In-situ phase transition from microemulsion to liquid crystal with the potential of prolonged parenteral drug delivery

This study is the first to investigate and demonstrate the potential of microemulsions (MEs) for sustained release parenteral drug delivery, due to phase transition behavior in aqueous environments. Phase diagrams were constructed with Miglyol 812N oil and a blend of (co)surfactants Solutol HS 15 and Span 80 with ethanol. Liquid crystal (LC) and coarse emulsion (CE) regions were found adjacent to the ME region in the water-rich corner of the phase diagram. Two formulations were selected, a LC-forming ME and a CE-forming ME and each were investigated with respect to their rheology, particle size, drug release profiles and particularly, the phase transition behavior. The spreadability in an aqueous environment was determined and release profiles from MEs were generated with gamma-scintigraphy. The CE-forming ME dispersed readily in an aqueous environment, whereas the LC-forming ME remained in a contracted region possibly due to the transition of ME to LC at the water/ME interface. Gamma-scintigraphy showed that the LC-forming ME had minimal spreadability and a slow release of 99mTc in the first-order manner, suggesting phase conversion at the interface. In conclusion, owing to the potential of phase transition, LC-forming MEs could be used as extravascular injectable drug delivery vehicles for prolonged drug release.