Liquid Crystalline Formation Research Articles

Recent advances and opportunities in MXene‐based liquid crystals

AbstractThe recent progress on the liquid crystalline (LC) dispersion of two‐dimensional (2D) transition metal carbides (MXenes) has propelled this unique nanomaterial into a realm of high‐performance architectures, such as films and fibers. Additionally, compared to architectures made from typical non‐LC dispersions, those derived from LC MXene possess tunable ion transport routes and enhanced conductivity and physical properties, demonstrating great potential for a wide range of applications, such as electronic displays, smart glasses, and thermal camouflage devices. This review provides an overview of the progress achieved in the production and processing of LC MXenes, including critical discussions on satisfying the required conditions for LC formation. It also highlights how acquiring LC MXenes has broadened the current solution‐based manufacturing paradigm of MXene‐based architectures, resulting in unprecedented performances in their conventional applications (e.g., energy storage and strain sensing) and in their emerging uses (e.g., tribology). Opportunities for innovation and foreseen challenges are also discussed, offering future research directions on how to further benefit from the exciting potential of LC MXenes with the aim of promoting their widespread use in designing and manufacturing advanced materials and applications.image

Effect of the Structure of Epoxy Monomers and Curing Agents: Toward Making Intrinsically Highly Thermally Conductive and Low-Dielectric Epoxy Resins.

The low intrinsic thermal conduction and high dielectric properties of epoxy resins have significantly limited their applications in electrical and electronic devices with high integration, high frequency, high power, and miniaturization. Herein, a liquid crystalline epoxy (LCE) monomer with a biphenyl mesogenic unit was first synthesized through an efficient one-step reaction. Subsequently, bisphenol AF (BPAF) containing low-polarizable -CF3 groups and 4,4'-diaminodiphenylmethane (DDM) were applied to cure the LCE and commercial diglycidyl ether of bisphenol A-type epoxy (E-51), respectively, to afford four kinds of epoxy resins with various intrinsic thermal conductivity and dielectricity values. Owing to the dual effect of microscopically stacking of mesogens and the contribution of fluorine to the formation of liquid crystallinity, ordered microstructures of the nematic liquid crystal phase were formed within the cross-linking network of LCE as confirmed by polarized optical microscopy and X-ray diffraction. Consequently, phonon scattering was suppressed, and the intrinsic thermal conductivity was improved considerably to 0.38 W/(m·K), nearly twice as high as that of E-51 cured with DDM (0.20 W/(m·K)). Additionally, the ordered microstructure and ultralow polar -CF3 groups within LCE cured with BPAF enabled the epoxy resin to exhibit a remarkably lower and stable dielectric constant (ε) and dielectric loss tangent (tan δ) over both low and high frequencies compared to E-51 cured with DDM. The ε decreased from 3.40 to 2.72 while the tan δ decreased from 0.044 to 0.038 at 10 GHz. This work presents a scalable and facile strategy for breaking the bottleneck of making epoxy resins simultaneously with high inherent thermal conduction and low dielectric performance.

Liquid crystalline phase behavior and hydration of hydroxypropyl cellulose in water: A liquid and solid NMR investigation

AbstractHydroxypropyl cellulose (HPC) is a functional material with numerous applications as a drug solubilizer, thickener, and stabilizer. Herein, the mobile and rigid regions of HPC are investigated using liquid‐ and solid‐state NMR, respectively, in the high‐viscosity regime of concentrated aqueous samples, below and above the formation of an ordered chiral liquid‐crystalline (LC) mesophase. Liquid NMR 13C relaxation and hydration studies reveal that hydroxypropyl pendant chains remain more fluid than the pyranose sugar rings at concentrations below the formation of the LC phase. The inner part of the pendant chains close to the cellulose backbone exhibits a higher water structuration and a lower water renewal than the outer part and the pyranoses, which likely compensates for their higher hydrophobicity. When the LC phase is formed, the sample viscosity increases and the differences in flexibility and hydration of the pendant chains are reduced with respect to the pyranoses, while the whole system is rigidified. The system is not completely rigid even at concentrations above the formation of LC, as the interaction of water with the pyranoses considerably enhances their fluidity. In contrast, the pendant chains are much less affected.

Dielectric responses and stimulative optical shuttering action of self-assembly supramolecular hydrogen bond liquid crystalline formation via x- and y-types benzoic acids

Investigations of a single hydrogen bonded liquid crystals are made between alkyloxy benzoic acids (x-BOA) and alkyloxy benzoic acids (y-BOA) and are discussed in the present investigation. Type of mesogenic phases exhibited are visualized and recorded with the help of a Polarizing Optical Microscopy (POM). Conventional phases such as ‘Nematic’ (Nematic droplets, ‘Schlieren’ or threaded textures, four brush textures), ‘Smectic C’ (Schlieren and broken focal conical texture), ‘Smectic F’ (chequered board texture) and ‘Smectic G’ (multi colored smooth mosaic texture) are observed. Newly investigated textural phases viz., ‘Smectic X’ (‘worm’ like texture) is also characterized to elucidate their structure. Phase diagrams are constructed to study in detail the thermal stability, occurrence and thermal span of the phases as a function of the chemical constitution of hydrogen bonded (HB) complexes. Thermal analysis include analysis of Differential Scanning Calorimetry (DSC) thermograms, study of the order of the transition by Navard & Cox parameter and construction of the relevant phase diagrams. Electrical attempts include measurement of permittvity and dielectric loss with respect to the electrical stimulus applied and light intensity profile analysis.

Bacillus licheniformis levan as a functional biopolymer in topical drug dosage forms: From basic colloidal considerations to actual pharmaceutical application

Ongoing demand in sustainable and biocompatible drug dosage forms is reflected in the search for novel pharmaceutical excipients with equal properties. A group of microbial exopolysaccharides offers a variety of biopolymers with many alleged uses and effects. This study aims to assess applicative properties of levan obtained from Bacillus licheniformis NS032, focusing on its potential co-stabilizing and drug release-controlling functions in pertaining emulsion systems. Despite its high molecular weight and partial existence in globular nanometric structures (180-190 nm), levan was successfully incorporated into both tested colloidal systems: those stabilized with synthetic/anionic or natural-origin/non-ionic emulsifiers. In the tested levan concentrations range (0.2-3.0% w/w) the monitored flow and thermal parameters failed to show linear concentration dependence, which prompted us to revisit certain colloidal fundamentals of this biopolymer. Being a part of the external phase of the investigated emulsion systems, levan contributed to formation of a matrix-like environment, offering additional stabilization of the microstructure and rheology modifying properties (hysteresis loop elevation as high as 4167±98 to 20792±3166 Pa•s−1), especially in case of the samples where lamellar liquid crystalline formation occurred. Apart from its good water solubility and considerable conformational flexibility, the investigated homofructan easily saturated the external phase of the samples stabilized with a conventional anionic emulsifier, leading to similar properties of 0.2% and 3.0% levan-containing samples. After closer consideration of thermal and release behavior, this was considered as a favorable property for a novel excipient, offering tailored formulation characteristics even with lower levan concentrations, consequently not compromising the potential cost of the final drug dosage form.

Liquid-Crystalline Hydroxyapatite/Polymer Nanorod Hybrids: Potential Bioplatform for Photodynamic Therapy and Cellular Scaffolds.

Recently, we found that self-organization of hydroxyapatite (HAp) with poly(acrylic acid) (PAA) leads to the formation of liquid-crystalline (LC) nanorod hybrids that form aligned films and show stimuli-responsive properties. Here, we demonstrate that these biocompatible HAp/PAA hybrid nanorods represent a platform technology as drug nanocarriers for photodynamic cancer therapy and as bioscaffolds for the control of cellular alignment and growth. To use hybrid nanorods as a drug nanocarrier, we introduced methylene blue (MB), a typical photosensitizer for photodynamic therapy, into the PAA nanolayer covering the surface of the HAp nanocrystals through electrostatic interactions. The stable MB-loaded HAp/PAA hybrid nanorods efficiently produced singlet oxygen from MB upon light irradiation and showed remarkable photodynamic therapeutic effects in cancer cells. Moreover, taking advantage of the mechanically responsive LC alignment properties of the HAp/PAA hybrid nanorods, macroscopically oriented bioscaffolds were prepared through a spin-coating process. The cells cultured on the oriented scaffolds showed cellular alignment and elongation along the oriented direction of the hybrid nanorods. The HAp/PAA hybrid nanorods demonstrate potential in drug delivery and tissue engineering. These unique LC HAp/PAA hybrid nanorods have significant potential as a platform for the development of various types of biomaterial.

Physicochemical characterization of 6-O-acyl trehalose fatty acid monoesters in desiccated system

The understanding of the basic physicochemical properties of trehalose lipid is indispensable to extending their availability. In this study, the hydrate crystal (Cr), the liquid crystalline (LC) phase and the glassy state formations of 6-O-acyl trehalose fatty acid monoester (TREn) were examined under in a desiccated system. TREn (n = 10, 12, 14, 16) formed monohydrate Cr and showed the hydrate Cr-glassy fluid lamellar LC (Lα) phase transition via dehydration in the heating process. Here, Lα phase for TRE10 and TRE12 was kinetically formed by the dehydration below the glass transition temperature (Tg). On the dehydration temperature (Tdeh), Tgs, and heat capacity changes (ΔCps) at these Tgs, no distinct effects by the difference of the acyl chain length were recognized, possibly because the core structure of containing sugar hydrate Cr or sugar moieties should be similar regardless of the acyl chain length. Besides, TRE10 having a relatively high hydrophilic/hydrophobic balance (HLB) afforded to form the cubic LC (Q) phase and the corresponding glassy phase, while TRE14 and TRE16 having low HLB afforded the Lα phase as well as the corresponding glassy phases above Tg. TRE12 having middle HLB afforded both LCs and the corresponding glassy phase by controlling the kinetics of LC-LC phase transition between Lα and Q phases. Furthermore, the anomalous reversible phase transition during both the heating and cooling processes was also ascertained in the glassy phase for TRE16, which was considered the phase transition between glassy Lα and glassy lamellar gel (Lβ) phase. It greatly empathizes the two-dimensional trehalose glass layer and fluid hydrocarbon chains in the TREn glassy phase. Thus, in this study, it was demonstrated that TREn as the simplest trehalose lipid exhibited the glassy formation performance as well as the hydrate Cr formation, which showed less chain length dependence, together with the LC formation and the phase transition between glassy Lα and glassy Lβ phase, which depended on chain length greatly.

Kinetics of the catalytic polymerization of pyrene with AlCl3

The kinetics of the catalytic polymerization of pyrene monomer to pyrene pitch in the presence of aluminum trichloride (AlCl3) were studied at temperatures between 330 and 370 °C in a 1-L batch reactor. Both reactants and reaction products were isolated from the bulk pitch using supercritical extraction (SCE), so that they could be quantified. Concentrations of monomer, dimer, and trimer were measured at discrete reaction times, and each was found to exhibit first-order reaction behavior. Analysis of the oligomerization reaction behavior at differing temperatures enabled the calculation of apparent activation energies and pre-exponential factors for each reaction. Relatively low activation energies that decreased with increasing oligomer size were obtained, suggesting that the reactions are mass-transfer-limited. The microkinetic model that was developed can be used to estimate the reaction time for which the formation of liquid crystalline, mesophase-forming pyrene trimer is maximized. Other groups have developed models for bulk mesophase formation, but this is the first time that reaction kinetics have been measured for individual oligomers in a carbonaceous pitch formed from pure polycyclic aromatic hydrocarbons (PAHs) or mixtures thereof.

Filamentous Viruses as Building Blocks for Hierarchical Self-Assembly toward Functional Soft Materials

Abstract This review describes the utilization of M13 phage, one of the filamentous viruses, for the development of novel functional soft materials. Traditionally, M13 phage has been widely used as a scaffold to display peptides or proteins on the surface of M13 phage through genetic engineering. This technology is well known as “phage display”, and generally used nowadays for the construction of peptide or protein libraries on M13 phage surfaces to identify peptides or proteins with desired functions. Recently, construction of hierarchical assembled structures composed of M13 phage as a building block has generated great interest as a means of using the excellent properties of M13 phage for the development of novel classes of soft materials. In this case, liquid crystalline formation of M13 phage is effectively used to fabricate structurally regulated assemblies. Further combination of the phage display technique and liquid crystalline formation widely expands the applicability of M13 phage to various fields such as devices, sensors, and biomedicines. Such approaches to M13 phage should contribute to novel attractive opportunities for next-generation soft materials for science and technology.

The alkyl polyglucoside/fatty alcohol ratio effect on the formation of liquid crystal phases in binary systems

The present research focuses on the alkyl polyglucoside, a non-ionic surfactant, in combination with a fatty alcohol of the same chain length used as a co-surfactant. A series of solutions were prepared, with varying both APG/FA ratio and its concentration in water. Different structures were then obtained, depending on these two parameters: aqueous micellar solutions, normal hexagonal liquid crystalline phase, α-gel phase, as well as the mixture of normal hexagonal/α-gel phases. A specific term “auto-emulsion” was introduced to describe the pseudo emulsions formed by the APG≤FA containing solutions because of the fatty alcohol, which dispersion in water was similar to an emulsion representation. The presence of the liquid crystals was revealed by optical microscopy under the polarized light, as different anisotropic conformations corresponding to the lamellar phase, the hexagonal phase and the coexistence of the lamellar and hexagonal phases, mainly for the most concentrated samples, were observed. These structures were characterized at the molecular level through the wide-angle X-ray diffraction technique and their macroscopic behaviour was investigated by rheology tests. Two main observations were then made: the variation of the surfactant concentration in solution promotes the transition between micellar region towards the liquid crystalline formation zone, while the APG/FA ratio impacts the formation of hexagonal phases (APG>FA) or of lamellar ones (APG<FA).

Filamentous virus-based soft materials based on controlled assembly through liquid crystalline formation

This focus review describes the utilization of M13 phage, a filamentous virus, for the development of a novel class of materials. Historically, M13 phage has been widely utilized as a scaffold to display desired peptides or proteins on the surface through genetic engineering. This biotechnology is well known as ‘phage display’ and has generally been used for constructing peptide libraries on M13 phage surfaces to screen peptides with a specific affinity for desired molecules or materials. Recently, the preparation of ordered structures composed of M13 phages based on liquid crystal formation has generated great interest as a means of utilizing the outstanding properties of phages for the development of novel soft materials. The combination of phage display technologies and liquid crystal formation can be effectively used to develop structurally regular hybrid materials composed of M13 phages and inorganic or organic materials. M13 phages can be used, for example, as polymeric materials to construct structurally regular hybrid hydrogels, hydrogel matrices for controlled release systems, selective adsorbents for rare earth elements and protein-detecting microarray systems. The excellent properties of M13 phages should further contribute to novel attractive opportunities of next-generation soft materials for science and technology. This focus review describes the utilization of M13 phage, a filamentous virus, for the development of a novel class of materials. Recently, the preparation of ordered structures composed of M13 phages based on liquid crystal formation has generated great interest as a means of utilizing the outstanding properties of phages for the development of novel soft materials. The combination of genetic engineering-based functionalization and liquid crystal formation can be effectively used to develop structurally regular hybrid materials composed of M13 phages and inorganic or organic materials. M13 phages can be used for various functional soft materials.

An FT-IR spectroscopic study of the role of hydrogen bonding in the formation of liquid crystallinity for mixtures containing bipyridines and 4-pentoxybenzoic acid

The relationships between liquid crystallinity and hydrogen bonding are studied in mixtures containing 4-pentoxybenzoic acid, 5OBA, and five bipyridines, XBiPy, with spacers having different flexibilities, by Fourier transform infrared spectroscopy.

Synthesis and phase behavior of a new 2-vinylbiphenyl-based mesogen-jacketed liquid crystalline polymer with a high glass transition temperature and low threshold molecular weight

A new mesogen-jacketed liquid crystalline (LC) polymer was synthesized by NMP. It has a high Tg and a relatively low threshold MW for LC formation.

Relaxations in relation to Liquid Crystalline Formation and Glass Transition for Comb-like Polymer: Structural Relaxation as expressed by Entropy Model and Activation Energy Spectrum

This study demonstrates that the modelling approach for the kinetic phenomenon of glass transition is effective to examine the relaxation. In the enthalpy relaxation of poly(cyanobiphenyl-yloxy) alkyl acrylate, the decrease in enthalpy was measured as a function of ageing time and ageing temperature. Obtained data was analysed at first with the activation energy spectrum (AES) model, and next, with the framework of the entropy model which follows the evolution of the configurational entropy of the sample during the whole thermal history in the experiment. The prediction of DSC curve based on the result of analysis for the glass transition will be presented. AES model gives information about thermally activated processes which are available to contribute to observed enthalpy changes against the thermal history. The activated processes are relevant to the rearrangement of molecules. The rearrangement corresponds to the structural changes of polymer chain which can be observed in our study as the change in optical texture, known as the coarsening dynamics of nematic domain for the liquid crystalline materials. The analysis for the coarsening is also shown to elucidate the specific feature of physical parameter.DOI: http://dx.doi.org/10.3126/jncs.v30i0.9377Journal of Nepal Chemical Society Vol. 30, 2012 Page: 107-110 Uploaded date: 12/19/2013

Two-dimensional correlation infrared spectroscopy studies on the thermal-induced mesophase of 4-nitrobenzohydrazide derivative

Two-dimensional (2D) correlation infrared (IR) spectroscopy has been applied to explore the effect of hydrogen bondings (HBs) on the structure of mesophase in the dissymmetrical 4-nitrobenzohydrazide derivative, N-(4-cetyloxybenzoyl)-N′-(4′-nitrobenzoyl) hydrazine (C16-NO2). The strength and species of HBs as well as the heat-induced structural variations in mesophase have been investigated. It has been found from 2D correlation IR spectroscopy that the sequential order of changes in the different functionalities in the course of liquid crystalline formation is that, firstly, the alkyl chain changes from the significant population of the trans conformation to the significant population of gauche conformation; then, the intermolecular HB between CO and NH groups is weakened, some even being broken, and consequently, the intermolecular distance is enlarged; finally, the skeleton of phenyl ring has enough space to change their conformation to weaken the π–π stacking interaction. In addition, besides a few free and some medium bonded NH and CO groups, strongly bonded NH and CO groups still predominantly exist in the mesophase.

Scalable One‐Step Wet‐Spinning of Graphene Fibers and Yarns from Liquid Crystalline Dispersions of Graphene Oxide: Towards Multifunctional Textiles

AbstractKey points in the formation of liquid crystalline (LC) dispersions of graphene oxide (GO) and their processability via wet‐spinning to produce long lengths of micrometer‐dimensional fibers and yarns are addressed. Based on rheological and polarized optical microscopy investigations, a rational relation between GO sheet size and polydispersity, concentration, liquid crystallinity, and spinnability is proposed, leading to an understanding of lyotropic LC behavior and fiber spinnability. The knowledge gained from the straightforward formulation of LC GO “inks” in a range of processable concentrations enables the spinning of continuous conducting, strong, and robust fibers at concentrations as low as 0.075 wt%, eliminating the need for relatively concentrated spinning dope dispersions. The dilute LC GO dispersion is proven to be suitable for fiber spinning using a number of coagulation strategies, including non‐solvent precipitation, dispersion destabilization, ionic cross‐linking, and polyelectrolyte complexation. One‐step continuous spinning of graphene fibers and yarns is introduced for the first time by in situ spinning of LC GO in basic coagulation baths (i.e., NaOH or KOH), eliminating the need for post‐treatment processes. The thermal conductivity of these graphene fibers is found to be much higher than polycrystalline graphite and other types of 3D carbon based materials.

Structural Relaxations in Liquid Crystalline Formation and Glass Transition for Comb‐Like Polymer: Activation Energy Spectrum Analysis

SummaryThis study demonstrates that the modelling approach for the kinetic phenomenon of glass transition is effective to examine the relaxation. In the enthalpy relaxation of poly(cyanobiphenyl‐yloxy) alkyl acrylate, the decrease in enthalpy was measured as a function of ageing time and ageing temperature. Obtained data was analysed at first with the activation energy spectrum (AES) model, and next, with the framework of the entropy model which follows the evolution of the configurational entropy of the sample during the whole thermal history in the experiment. The prediction of DSC curve based on the analysis for the glass transition is presented. AES model gives information about thermally activated processes which are available to contribute to observed enthalpy changes against the thermal history. The activated processes are relevant to the rearrangement of the polymer chain. The effect of molecular weight on the peak maximum appeared in AES is reported.

Two-Dimensional Packing of Short DNA with Nonpairing Overhangs in Cationic Liposome–DNA Complexes: From Onsager Nematics to Columnar Nematics with Finite-Length Columns

We report the formation of liquid crystalline (LC) phases of short double-stranded DNA with nonpairing (nonsticky) overhangs, confined between two-dimensional (2D) lipid bilayers of cationic liposome-DNA complexes. In a landmark study (Science2007, 318, 1276), Nakata et al. reported on the discovery of strong end-to-end stacking interactions between short DNAs (sDNAs) with blunt ends, leading to the formation of 3D nematic (N) and columnar LC phases. Employing synchrotron small-angle X-ray scattering, we have studied the interplay between shape anisotropy-induced and DNA end-to-end interaction-induced N ordering for 11, 24, and 48 bp sDNA rods with single-stranded oligo-thymine (T) overhangs modulating the end-to-end interactions. For suppressed stacking interactions with 10-T overhangs, the volume fraction of sDNA at which the 2D isotropic (I)-to-N transition occurs for 24 and 48 bp sDNA rods depended on their length-to-width (L/D) shape anisotropy, qualitatively consistent with Onsager's theory for the entropic alignment of rigid rods. As the overhang length is reduced from 10 to 5 and 2 T for 24 and 48 bp sDNA, the N-to-I transition occurs at lower volume fractions, indicating the onset of some degree of end-to-end stacking interactions. The 11 bp sDNA rods with 5- and 10-T overhangs remain in the I phase, consistent with their small shape anisotropy (L/D ≈ 1.9) below the limit for Onsager LC ordering. Unexpectedly, in contrast to the behavior of 24 and 48 bp sDNA, the end-to-end interactions between 11 bp sDNA rods with 2-T overhangs set in dramatically, and a novel 2D columnar N phase (N(C)) with finite-length columns formed. The building blocks of this phase are comprised of 1D stacks of (on average) four 11 bp DNA-2T rods with an effective L(stacked)/D ≈ 8.2. Our findings have implications for the DNA-directed assembly of nanoparticles on 2D platforms via end-to-end interactions and in designing optimally packed LC phases of short anisotropic biomolecules (such as peptides and short-interfering RNAs) on nanoparticle membranes, which are used in gene silencing and chemical delivery.

Imidazolium camphorsulfonamides: Chiral catanionic liquid crystals with tunable thermal properties

We report the synthesis of novel chiral catanionic liquid crystals bearing camphorsulfonamide substructures. The phase behaviour of these long-chain substituted imidazolium sulphates and sulfonates was investigated using X-ray diffraction (XRD), polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). We observed that the phase behaviour clearly depends on the substitution of both cation and anion. The chiral camphorsulfonamide substructures have an unfavourable influence on the formation of liquid crystalline (LC-) phases. Contrary to N, N′-di-alkyl-imidazolium salts, the formation of LC phases was only observed when both cation and anion are substituted with long alkyl chains (C 12 or C 16). Furthermore, the phase transition temperatures depend on the chain length of the alkyl groups, as higher phase transition temperatures were observed for compounds bearing longer alkyl chains. However, no macroscopic evidence for the formation of chiral mesophases was obtained.

Bending Deformation Mechanism and Defective Properties of Liquid Crystalline Carbon Nanotubes in Evaporating Droplets

Here, we explore the liquid crystalline behavior of carbon nanotubes (CNTs) through two types of commonly physical parameters (the Frank elastic constants kii (i = 1, 2, 3) in the liquid crystal field that typically describe the nature of molecular orientation, and the Young's modulus E that characterizes the peculiar mechanical properties of CNTs). Droplets of aqueous multiwall carbon nanotube (MWNT) suspensions are evaporated on silica wafer at room temperature in air and the resultant deposits exhibit the hallmark property of liquid crystalline formation, birefringence. And scanning electron microscopic (SEM) characterization further presents the concentric bending arrangement of MWNTs along the circumference at the edge. Then in analogy with liquid crystals, based upon the restraint of circular boundary as in the model of droplets, the CNTs' Frank elasticity is introduced and expresses the relationship with E, showing the dependence of nanotube rigidity and dimensions. By comparing the values of plane parameters k11 and k33, defective properties about CNT-assemblies are provided, with Frank elastic constant anisotropy (k11 ≠ k33) contributing to their various distortion structures in the central core of the defects.