Structure Of Liquid Crystalline Phases Research Articles

Thermal Conductivity and Orientation Structure of Liquid Crystalline Epoxy Thermosets Prepared by Latent Curing Catalyst

Improvements in the performance of electronic devices necessitate the development of polymer materials with heat dissipation properties. Liquid crystalline (LC) epoxies have attracted attention because of the orientation of their polymer network chains and their resultant high thermal conductivity. In this study, a diglycidyl ether of 1-methyl-3-(4-phenylcyclohex-1-enyl)benzene was successfully synthesized as an LC epoxy and the LC temperature range was evaluated via differential scanning calorimeter (DSC). The synthesized LC epoxy was cured with m-phenylenediamine (m-PDA) as an amine-type curing agent and 1-(2-cyanoethyl)-2-undecylimidazole (CEUI) as a latent curing catalyst, respectively. The LC phase structure and domain size of the resultant epoxy thermosets were analyzed through X-ray diffraction (XRD) and polarized optical microscopy (POM). High thermal conductivity was observed in the m-PDA system (0.31 W/(m·K)) compared to the CEUI system (0.27 W/(m·K)). On the other hand, in composites loaded with 55 vol% Al2O3 particles as a thermal conductive filler, the CEUI composites showed a higher thermal conductivity value of 2.47 W/(m·K) than the m-PDA composites (1.70 W/(m·K)). This difference was attributed to the LC orientation of the epoxy matrix, induced by the hydroxyl groups on the alumina surface and the latent curing reaction.

High toughness and thermal conductivity of thermosets from liquid crystalline epoxy with low melting point

AbstractA diphenylcyclohexene‐type liquid crystalline (LC) epoxy was successfully synthesized and characterized by proton nuclear magnetic resonance (1H‐NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and gel permeation chromatography (GPC). Even though the synthesized epoxy monomer showed a low melting temperature (99°C), the LC (smectic and nematic) phase was maintained over a wide temperature range of 99–184°C during the heating process. Moreover, the synthesized LC epoxy was cured with 4,4′‐diaminodiphenylmethane under four different temperature conditions. The LC phase structure, domain size, and LC fraction of the resulting epoxy thermosets were analyzed by X‐ray diffraction (XRD) and polarized optical microscopy (POM). The fracture toughness and thermal conductivity increased with an increase in the size and volume fraction of the LC domains. It was also found that the enhancement of the fracture toughness was more sensitive than that of the thermal conductivity.

3D Lipidic Matrix for Incorporation and Stabilization of Biologically Active Molecules

In aqueous media, biologically active substances are usually unstable, poorly soluble compounds with low bioavailability. Incorporation of these compounds into the structure of lipid-based lyotropic liquid crystalline phase or nanoparticles can increase their solubility and subsequent bioavailability. The aim of this review is to clarify the principle of self-assembly of lipidic amphiphilic molecules in the aqueous environment, to present lipid bicontinuous cubic and hexagonal phases and their current biological application.

Thermal conductivity enhancement of liquid crystalline epoxy/MgO composites by formation of highly ordered network structure

AbstractTo develop a high thermal conductive composite, an MgO filler was incorporated into a liquid crystalline (LC) epoxy containing a mesogenic moiety. The thermal conductivity of the obtained composite was 1.41 W/(m∙K) at 33 vol% content, which was remarkably higher than the value predicted using Bruggeman's model. To investigate the reason for this significant enhancement of the thermal conductivity in the LC epoxy composites, the LC phase structure of the composite was analyzed by a polarized optical microscope, an X‐ray diffractometry (XRD) and a polarized IR mapping measurement. An XRD analysis indicated the local formation of a highly ordered smectic phase structure, even in the high‐loading composite. This result indicated the promotion of the self‐assembly of the mesogenic network polymer chains by the MgO filler loading. We considered that this highly ordered structural formation can lead to an increase in the matrix resin's thermal conductivity, which can result in the effective enhancement of the thermal conductivity in the LC epoxy/MgO composite.

Origin and structure of liquid crystalline Blue Phase III

We report here an off-lattice NVT molecular dynamics simulation study of a system of polar chiral ellipsoidal molecules, which spontaneously exhibits Blue Phase III (BPIII), considering coarse-grained attractive-repulsive pair interaction appropriate for anisotropic liquid crystal mesogens. We have observed that suitable selection of chiral and dipolar strengths not only gives rise to thermodynamically stable BPIII but novel Smectic and Bilayered BPIII as well. Further, we have demonstrated that the occurrence of BPIII and its layered counterparts depend crucially on molecular elongation.

Mesoscale structure of wrinkle patterns and defect-proliferated liquid crystalline phases

Thin solids often develop elastic instabilities and subsequently complex, multiscale deformation patterns. Revealing the organizing principles of this spatial complexity has ramifications for our understanding of morphogenetic processes in plant leaves and animal epithelia and perhaps even the formation of human fingerprints. We elucidate a primary source of this morphological complexity-an incompatibility between an elastically favored "microstructure" of uniformly spaced wrinkles and a "macrostructure" imparted through the wrinkle director and dictated by confinement forces. Our theory is borne out of experiments and simulations of floating sheets subjected to radial stretching. By analyzing patterns of grossly radial wrinkles we find two sharply distinct morphologies: defect-free patterns with a fixed number of wrinkles and nonuniform spacing and patterns of uniformly spaced wrinkles separated by defect-rich buffer zones. We show how these morphological types reflect distinct minima of a Ginzburg-Landau functional-a coarse-grained version of the elastic energy, which penalizes nonuniform wrinkle spacing and amplitude, as well as deviations of the actual director from the axis imposed by confinement. Our results extend the effective description of wrinkle patterns as liquid crystals [H. Aharoni et al, Nat. Commun. 8, 15809 (2017)], and we highlight a fascinating analogy between the geometry-energy interplay that underlies the proliferation of defects in the mechanical equilibrium of confined sheets and in thermodynamic phases of superconductors and chiral liquid crystals.

Synthesis of modifiable photo-responsive polypeptides bearing allyloxyazobenzene side-chains

A photo-responsive and modifiable polypeptide with stable helical conformation was synthesized. The self-assembly and liquid crystalline phase structure were subsequently studied.

Vancomycin ocular delivery systems based on glycerol monooleate reversed hexagonal and reversed cubic liquid crystalline phases

Lyotropic bulk reversed hexagonal and reversed cubic liquid crystalline phases (hexagonal and cubic phases) composed of glycerol monooleate (GM) were used to design the vancomycin hydrochloride’s (VHCl) delivery systems aiming to maintain VHCl’s therapeutic concentration during 24 h in the eye, locally (as an insert) and/or intravitreally (as a bulk phase injection).Bulk VHCl’s hexagonal and cubic phases were successfully prepared by melted homogenization and solvent evaporation method, and then an insert was prepared.The structural characteristics of liquid crystalline phases were studied using cross polarized light microscopy and small angle X-ray scattering technique. The presence of VHCl (1–9.5% w/w VHCl solution) did not exhibit any change in the liquid crystalline phase’s structure to another liquid crystalline phase, and showed little effect on the lattice parameter of the existing liquid crystalline phase structure.In order to relate the liquid crystalline phase structure to VHCl’s release rate locally into the eye, in-vitro release test of an implant has been done using a simulated tear fluid. VHCl’s release in the simulated tear fluid from the cubic phase obeyed Higuchi kinetics, with linear VHCl’s release versus the square root of time. The hexagonal phase released VHCl in simulated tear fluid significantly slower than the cubic phase. In order to relate the liquid phase structure to VHCl’s diffusion intravitreally, in vitro release test by the Sirius‘ Subcutaneous Injection Site Simulator (Scissor) has been performed. Comparing the release properties by a Scissor, the VHCl’s cubic phase demonstrated slower permeation through extra-cellular matrix than the VHCl solution.To evaluate the efficacy of the system investigated, the release properties of VHCl’s cubic phase were compared with literature data indicating that the cubic phase could be a potential matrix system in the delivery of VHCl intravitreally during 24 h after intravitreal injection. The release data in the simulated tear fluid indicated that the cubic phase should be further optimized to achieve a therapeutic VHCl concentration locally in the eye during 24 h.

On the Molecular Interactions in Lipid Bilayer-Water Assemblies of Different Curvatures.

This work concerns the importance of intermolecular interactions present in aqueous lipid assembly systems depending on the type of aggregates they form. We have studied aqueous mixtures of diglycerol monooleate, Capmul glycerol monoleate (GMO-50) and polyoxyethylene (20) sorbitan monooleate (Polysorbate 80, P80) using small-angle X-ray scattering (SAXS) measurements to reveal the structure of liquid crystalline phases. On the basis of the SAXS data, a phase diagram was constructed. We discuss the effect of curvature changes of the lipid-aqueous interface obtained by changing the water content and the temperature. The results are related to the intermolecular interactions, as revealed by Raman spectroscopy, with a focus on the bilayer type of system of different curvature and bilayer flexibility, namely, the lamellar phase, bicontinuous cubic phase, and sponge phase. All phases show large similarities in their chain conformation and head group interactions as revealed by the Raman spectra, arising from the fact that all three structures are formed by lipid bilayers. However, subtle differences in the molecular organization of the sponge phase were revealed by employing Raman difference spectroscopy and by analysis of key spectroscopic indicators, which show a less dense hydrocarbon chain packing compared to the inverse bicontinuous cubic or lamellar phase.

Immune responses induced by nano-self-assembled lipid adjuvants based on a monomycoloyl glycerol analogue after vaccination with the Chlamydia trachomatis major outer membrane protein

Nanocarriers based on inverse hexagonal liquid crystalline phases (hexosomes) show promising potential as vaccine delivery systems. Their unique internal structure, composed of both lipophilic domains and water-containing channels, renders them capable of accommodating immunopotentiating compounds and antigens. However, their adjuvant properties are poorly understood. We hypothesized that the supramolecular structure of the lyotropic liquid crystalline phase influences the immunostimulatory activity of lipid-based nanocarriers. To test this, hexosomes were designed containing the lipid phytantriol (Phy) and the immunopotentiator monomycoloyl glycerol-1 (MMG-1). Self-assembly of Phy and MMG-1 into nanocarriers featuring an internal hexagonal phase was confirmed by small-angle X-ray scattering and cryogenic transmission electron microscopy. The effect of the nanostructure on the adjuvant activity was studied by comparing the immunogenicity of Phy/MMG-1 hexosomes with MMG-1-containing lamellar liquid crystalline nanoparticles (liposomes, CAF04). The quality and magnitude of the elicited immune responses were determined after vaccination of CB6/F1 mice using the Chlamydia trachomatis major outer membrane protein (MOMP) as antigen. MMG-1-based hexosomes potentiated significantly stronger MOMP-specific humoral responses than CAF04 liposomes. The liposome-based vaccine formulation induced a much stronger MOMP-specific cell-mediated immune response compared to hexosome-adjuvanted MOMP, which elicited minimal MOMP-specific T-cell stimulation after vaccination. Hence, our data demonstrates that hexosomal and liposomal adjuvants activate the immune system via different mechanisms. Our work provides valuable insights into the adjuvant potential of hexosomes and emphasizes that engineering of the supramolecular structure can be used to design adjuvants with customized immunological properties.

Tuning Structures of Mesogen‐Jacketed Liquid Crystalline Polymers and Their Rod–Coil Diblock Copolymers by Varying Chain Rigidity

AbstractTwo mesogen‐jacketed liquid crystalline (LC) polymers with different rigid side‐chain cores, poly[2,5‐bis(tert‐butoxylcarbonyl)styrene] (PM1) and poly[2,5‐bis(4‐tert‐butoxylcarbonyl phenyl)styrene] (PM3), as well as their corresponding block copolymers (BCPs), poly(dimethylsiloxane)‐b‐PM1 (PDMS‐b‐PM1) and PDMS‐b‐PM3, are synthesized and characterized. The LC phase structures of the homopolymers and the microphase‐separated structures of the BCPs can be controlled by changing the rigidity of the polymer chains with the different rigid side‐chain cores used. The LC phase structure of PM1 homopolymer is dependent on its molecular weight (MW). On the other hand, PM3 is always amorphous below thermal decomposition temperature regardless of its MW, owing to much higher rigidity of PM3 compared with that of PM1. Although both BCPs can self‐assemble into lamellae (LAM) and hexagonally packed cylinders (HEX) with varying compositions, PDMS‐b‐PM3 can form the HEX structure at a smaller weight fraction of the PM3 block because PDMS‐b‐PM3 possesses a larger geometric asymmetric factor compared with PDMS‐b‐PM1. For PDMS‐b‐PM1 with a large enough MW, it can form hierarchically ordered nanostructures, including the LAM or HEX nanostructure of the BCP and the columnar nematic phase of the PM1 block.

Factors affecting the structure of lyotropic liquid crystals and the correlation between structure and drug diffusion.

Lyotropic liquid crystals (LLCs) formed by the self-assembly of amphiphilic molecules in a solvent (usually water) have attracted increasingly greater attention in the last few decades, especially the lamellar phase (Lα), the reversed bicontinuous cubic phase (Q2) and the reversed hexagonal phase (H2). Such phases offer promising prospects for encapsulation of a wide range of target molecules with various sizes and polarities owing to the unique internal structures. Also, different structures of mesophases can give rise to different diffusion coefficients. The bicontinuous cubic phase and the hexagonal phase have been demonstrated to control and sustain the release of active molecules. Furthermore, the structures are susceptible to many factors such as water content, temperature, pH, the presence of additives etc. Many researchers have been studying these influencing factors in order to accurately fabricate the desired phase. In this paper, we give a review of the characteristics of different structures of liquid crystalline phases, the influencing factors on the phase transition of liquid crystals and the relationship between structures of LLC and drug diffusion. We hope our review will provide some insights into how to manipulate in a controlled manner the rate of incorporating and transferring molecules by altering the structure of lyotropic mesophases.

Influence of alkyl tail length on self-organisation of side-chain liquid crystalline polymers with biphenyl hemiphasmidic mesogens

ABSTRACTA new and simple series of side-chain liquid crystalline polymethacrylates containing biphenyl hemiphasmidic mesogens based on 4-[(3,4,5-trialkan)-1-carbonylbenzoate]biphenyl (denoted as PTmBMA, m = 6, 8, 10, 12, 14, 16, 18, m refers to the carbon number of alkoxy tails) groups was designed and successfully synthesised via free radical polymerisation. The phase structures and transitions of the polymers were investigated by the combination of techniques including differential scanning calorimetry, polarizing microscope, one-dimensional/two-dimensional wide-angle X-ray diffraction, and small-angle X-ray scattering. The experimental results revealed that the liquid crystalline phase structures and behaviours of the polymers were found to be strongly dependent on the alkyl tail length (m). When m = 6, the PTmBMA formed a stable smectic phase above Tg. When m = 8, 10, 12, 14, 16, 18, the sample presented a hexagonal columnar mesophase (Φh), suggesting that the alkyl length has played an important role in the phase behaviours of hemiphasmidic side-chain liquid crystalline polymers.

Liquid Crystalline Epoxies with Lateral Substituents Showing a Low Dielectric Constant and High Thermal Conductivity

In this work, liquid crystalline epoxies with lateral substituents were synthesized and cured with aromatic amines or anhydride. The liquid crystalline phase structure of liquid crystalline epoxies with lateral substituents was determined by polarized optical microscopy. The relationship between thermal conductivity and dielectric properties and liquid crystalline domain structure was discussed in the paper. The samples show high thermal conductivity up to 0.29 W/(m × K), due to the orientation of mesogenic units in epoxies. The sample's low dielectric constant of 2.29 is associated with the oriented mesogenic units and long nonpolar lateral substituents. This indicates a new way to obtain materials with high thermal conductivity and a low dielectric constant by introducing oriented mesogenic units into cross-linked epoxy systems. The water repellency is reflected in the contact angles of 92–98°, which are apparently higher than that of conventional epoxy systems. It was also found that the better toughness of liquid crystalline epoxies with lateral substituents was attributed to the existence of long flexible alkyl lateral substituents.

Cationic liposome-nucleic acid nanoparticle assemblies with applications in gene delivery and gene silencing.

Cationic liposomes (CLs) are synthetic carriers of nucleic acids in gene delivery and gene silencing therapeutics. The introduction will describe the structures of distinct liquid crystalline phases of CL-nucleic acid complexes, which were revealed in earlier synchrotron small-angle X-ray scattering experiments. When mixed with plasmid DNA, CLs containing lipids with distinct shapes spontaneously undergo topological transitions into self-assembled lamellar, inverse hexagonal, and hexagonal CL-DNA phases. CLs containing cubic phase lipids are observed to readily mix with short interfering RNA (siRNA) molecules creating double gyroid CL-siRNA phases for gene silencing. Custom synthesis of multivalent lipids and a range of novel polyethylene glycol (PEG)-lipids with attached targeting ligands and hydrolysable moieties have led to functionalized equilibrium nanoparticles (NPs) optimized for cell targeting, uptake or endosomal escape. Very recent experiments are described with surface-functionalized PEGylated CL-DNA NPs, including fluorescence microscopy colocalization with members of the Rab family of GTPases, which directly reveal interactions with cell membranes and NP pathways. In vitro optimization of CL-DNA and CL-siRNA NPs with relevant primary cancer cells is expected to impact nucleic acid therapeutics in vivo. This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.

Relaxation behavior of supra-molecular hydrogen-bonded liquid crystal phase structures: SA:11OBA

ABSTRACTLow-frequency (20 Hz–10 MHz) dielectric response in liquid crystalline (LC) phases of hydrogen-bonded (HB) complex, SA:11OBA, is studied. Synthesis of SA:11OBA with non-mesogenic succinic acid (SA) and mesogenic p-n-undecyloxy benzoic acid (11OBA) and its spectroscopic confirmation are detailed. Phase transition temperatures (TC) involving nematic, smectic-C (SmC), and smectic-G (SmG) phases by capacitance C(T) and loss tanΔ(T) anomaly agree with the microscopy (polarizing optical microscope) and calorimetry (differential scanning calorimetry) results. Low-frequency dispersion infers two types of reorientation processes, viz. higher frequency (∼MHz) and lower frequency (kHz) processes. Distinct time scale mechanism are presented. Arrhenius behavior infers influence of HB on activation energy (Ea). Off-centered dispersion, viz. ϵ′(ω) with ϵ″(ω), analyzed through the Cole–Cole plots in N, SmC, and SmG phases infers a strong temperature trend for dielectric strength (Δϵ) and distribution (α) parameters. Temperature dependence of α-parameter reveals on LC phases increasing fixture of molecular dipole in LC phase structure. Results are discussed in the wake of the body of data reported in LC phases exhibited by other LC compounds.

Influence of the spacer on the phase behaviors of side-chain liquid crystalline copolymers based on triphenylene discotic mesogen unit

Based on two analogous triphenylene liquid crystalline monomers (MTS and MT6S), a novel series of binary copolymers poly{[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]methacrylate-co-6-[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]hexyl methacrylate} (poly(MTSx-co-MT6Sy)) were prepared by free radical polymerization using AIBN as initiator. The random nature of the copolymers was expected on the basis of the assumed similar reactivities due to the analogous triphenylene monomers. The phase behaviors of copolymers were studied by DSC, POM and 1D WAXD. The results showed that the content of PMT6S has a significant effect on the liquid crystalline (LC) phase behaviors and phase structures of copolymers. The comparison between PMTS and PMT6S indicates that the content of the spacer was crucial to determine the LC structures. The PMTS formed a stable columnar nematic phase (ΦN) and the PMT6S exhibited a stable hexagonal columnar phase (ΦH). After copolymerization, the glass transition temperature and the phase transition temperature of the copolymers from the LC phase to isotropic phase both decreased with the molar fraction of PMT6S in the feed. The samples whose molar content of PMT6S was below 75% formed stable ΦN, similar to the property of PMTS. The samples whose molar content of PMT6S was above 80% presented the symmetry ΦH, similar to the property of PMT6S. Through copolymerization, one can better understand the interrelation of microstructures and how Tp mesogenic orders constitute the key basis for various applications.

High thermal conductivity epoxies containing substituted biphenyl mesogenic

In this work, a series of high thermal conductivity epoxies containing substituted biphenyl mesogenic were prepared and characterized. The liquid crystalline phase structure of substituted biphenyl epoxies was determined by polarized optical microscopy. Differential scanning calorimetry and thermogravimetric were used to characterize the thermal properties of substituted biphenyl epoxies. The relationship between thermal conductivity and liquid crystalline domain structure was discussed in our paper. The samples show high thermal conductivity up to 0.28 W/(m*K), owing to the introduction of biphenyl mesogenic into epoxes, which indicates that the thermal conductivity was apparently better than that of conventional epoxy systems. The high glass transition temperatures ranging from 128 to 178 °C and high thermal resistance can make contribute to a stable fixed shape. The high thermal conductivity and high thermal properties can make this epoxy very suitable for the application in microelectronics.

Molecular structure of the discotic liquid crystalline phase of hexa-peri-hexabenzocoronene/oligothiophene hybrid and their charge transport properties.

Using atomistic molecular dynamics simulation, we study the discotic columnar liquid crystalline (LC) phases formed by a new organic compound having hexa-peri-Hexabenzocoronene (HBC) core with six pendant oligothiophene units recently synthesized by Nan Hu et al. [Adv. Mater. 26, 2066 (2014)]. This HBC core based LC phase was shown to have electric field responsive behavior and has important applications in organic electronics. Our simulation results confirm the hexagonal arrangement of columnar LC phase with a lattice spacing consistent with that obtained from small angle X-ray diffraction data. We have also calculated various positional and orientational correlation functions to characterize the ordering of the molecules in the columnar arrangement. The molecules in a column are arranged with an average twist of 25° having an average inter-molecular separation of ∼5 Å. Interestingly, we find an overall tilt angle of 43° between the columnar axis and HBC core. We also simulate the charge transport through this columnar phase and report the numerical value of charge carrier mobility for this liquid crystal phase. The charge carrier mobility is strongly influenced by the twist angle and average spacing of the molecules in the column.

Tactile friction of topical formulations.

The tactile perception is essential for all types of topical formulations (cosmetic, pharmaceutical, medical device) and the possibility to predict the sensorial response by using instrumental methods instead of sensory testing would save time and cost at an early stage product development. Here, we report on an instrumental evaluation method using tactile friction measurements to estimate perceptual attributes of topical formulations. Friction was measured between an index finger and an artificial skin substrate after application of formulations using a force sensor. Both model formulations of liquid crystalline phase structures with significantly different tactile properties, as well as commercial pharmaceutical moisturizing creams being more tactile-similar, were investigated. Friction coefficients were calculated as the ratio of the friction force to the applied load. The structures of the model formulations and phase transitions as a result of water evaporation were identified using optical microscopy. The friction device could distinguish friction coefficients between the phase structures, as well as the commercial creams after spreading and absorption into the substrate. In addition, phase transitions resulting in alterations in the feel of the formulations could be detected. A correlation was established between skin hydration and friction coefficient, where hydrated skin gave rise to higher friction. Also a link between skin smoothening and finger friction was established for the commercial moisturizing creams, although further investigations are needed to analyse this and correlations with other sensorial attributes in more detail. The present investigation shows that tactile friction measurements have potential as an alternative or complement in the evaluation of perception of topical formulations.