Columnar Phase Research Articles

Nanoscale View of Alignment and Domain Growth in a Hexagonal Columnar Liquid Crystal.

Highly ordered liquid crystalline (LC) phases have important potential for organic electronics. We studied the molecular alignment and domain structure in a columnar LC thin film with nanometer resolution during in situ heating using four-dimensional scanning transmission electron microscopy (4D STEM). The initial disordered vapor-deposited LC glass thin film rapidly ordered at its glass transition temperature into a hexagonal columnar phase with small (<10 nm), well-aligned, planar domains (columns oriented parallel to the surface). Upon further heating, the domains coarsen via bulk diffusion, then the film crystallizes, then finally transforms back to an LC phase at an even higher temperature. The LC phase at high temperature shows straight columns of molecules, which we attribute to structure inherited from the intermediate crystalline phase. Nanoscale 4D STEM offers direct insight into the mechanisms of domain reorganization, and intermediate crystallization is a potential approach to manipulate orientational order and texture at the nano- to mesoscale in LC thin films.

In silico study of DNA mononucleotide self-assembly.

Recent experiments have demonstrated the self-assembly and long-range ordering of concentrated aqueous solutions of DNA and RNA mononucleotides. These are found to form Watson-Crick pairs that stack into columns that become spatially organized into a columnar liquid-crystalline phase. In this work, we numerically investigate this phase behavior by adopting an extremely coarse-grained model in which nucleotides are represented as semi-disk-like polyhedra decorated with attractive (patchy) sites that mimic the stacking and pairing interactions. We carry out Monte Carlo simulations of these patchy polyhedra by adapting algorithms borrowed from computer graphics. This model reproduces the features of the experimental phase behavior, which essentially depends on the combination of pairing and stacking interactions.

Microstructure and phase composition of Ti-coated cBN powders intended for active coating technology (ACT) processes

Development of an active coating technology (ACT) was aimed at fabricating high strength sinters using metallized powders like in case of titanium coated cubic boron nitride (cBN). It helps to avoid inhomogeneity in distribution of the binder phase during their mixing, being the main defects in such compacts. The information concerning phase composition of the coating formed over cBN during their metallization would be of much help as it concerns setting a proper sintering temperature securing both durable fusion of boride particles and elimination of porosity. Presently, two commercial Ti coated cBN powders are available, i.e. CBN-B-TA, 6–12 µm, from Van Moppes, Switzerland and CeraMicron CM-CBN 80 Ti, 20–30 µm, from Ceratonia, Germany (coded as cBN-VM and cBN-CM, respectively). The present investigation was aimed at characterization of the coatings microstructure and phase composition, being necessary for optimising sintering procedure. The scanning and transmission electron microscopy observations backed with energy dispersive X-ray microanalysis (SEM/TEM/EDS) showed that the cBN-VM particles carried a coating of thickness varying from 50 nm to 150 nm consisting of TiB and TiN phases, while the cBN-CM ones were covered by a much thicker (∼500 nm) coating built of mostly of TiB and TiN2-type crystallites. As the columnar nitride phases formed bulk of the coatings, though at the coating/cBN substrate boundary a nano-crystalline layer of TiB phase was documented in both powders. The crystallites of boride phase were accompanied by a strings of porosity. The XRD measurements indicated also presence of small amounts of the α-Ti(N) phase, which was probably intermixed with the other phases without forming a separate sub-layer. The thinner coating, i.e. one that formed over cBN-VM powder, was contaminated with Cl and K being a residue from the molten salts synthesis (MSS) deposition, as well as some surface oxides. The gathered information makes a basis for elaboration of new generation of cBN sinters of improved properties.

Ion‐Pairing Chromonic Liquid Crystals via Alternately Stacked Assembly of Amphiphilic Charged π‐Electronic Systems

In this study, a new assembly strategy for lyotropic chromonic liquid crystals (LCLCs) is proposed using iπ–iπ interactions, mainly comprising electrostatic and dispersion forces, between charged π‐electronic systems to form stacking structures supported by the hydration of triethylene glycol (TEG) units. Meso‐TEG‐aryl‐substituted porphyrin AuIII complex, an amphiphilic π‐electronic cation, showed diverse states and assembly modes in ion pairs depending on the coexisting counteranions. The PCCp– ion pair formed a hexagonal columnar (Colh) LC phase based on a charge‐by‐charge assembly, suggesting the formation of an ordered arrangement of charged p‐electronic systems through iπ–iπ interactions, with reduced interactions between the TEG chains. Furthermore, in the presence of water, LCLC behaviors in the Colh and nematic columnar phases according to the amount of water were observed for the PCCp– ion pair via iπ–iπ interactions. Magnetic‐field‐induced orientation of the charge‐by‐charge columnar structures upon dehydration was observed. Furthermore, single‐stranded charge‐by‐charge columnar structures, as components of the LCLCs, were observed using transmission electron microscopy (TEM).

Carbazole capped Schiff base and its boron difluoride complex as luminescent columnar phases with application as turn on chemosensor towards Al3+ as well as WLED

Three carbazole Schiff base derived hexacatenar liquid crystals (LCs) L/n (n = 12, 14, 16) composed of salicylaldimines as the central core with N-trialkoxylbenzyl carbazole capped at one side and trialkoxybenzoate capped at the other side have been synthesized. The BF2 complex of L/12 was also successfully prepared. Both carbazole Schiff bases L/n and BF2 complex L-BF2/12 can self-assemble into luminescent Colsqu/p4mm LC phases with local helical structures in their bulk states. L/n can additionally self-assemble into luminescent organogels with winkled morphologies. Study on the photophysical property indicates that both L/12 and its BF2 complex L-BF2/12 show large Stokes shift with yellow greenish emission. L/12 shows AIEE effect and can be applied as turn on Al3+ chemical sensors. BF2 complex L-BF2/12 with stronger emission than L/12 has been used to generate a white light emission diode (WLED).

Chirality and odd mechanics in active columnar phases.

Chiral active materials display odd dynamical effects in both their elastic and viscous responses. We show that the most symmetric mesophase with 2D odd elasticity in three dimensions is chiral, polar, and columnar, with 2D translational order in the plane perpendicular to the columns and no elastic restoring force for their relative sliding. We derive its hydrodynamic equations from those of a chiral active variant of model H. The most striking prediction of the odd dynamics is two distinct types of column oscillation whose frequencies do not vanish at zero wavenumber. In addition, activity leads to a buckling instability coming from the generic force-dipole active stress analogous to the mechanical Helfrich-Hurault instability in passive materials, while the chiral torque-dipole active stress fundamentally modifies the instability by the selection of helical column undulations.

A Donor-Acceptor Molecular Octopus and the CLICK Procedure in Columnar Liquid Crystal Phases.

Two star-shaped mesogens with a (meso-tetraphenylporphinato) zinc (II) core and bithiophene conjugated arms with 3,4,5-trisdodecyloxyphenyl periphery were synthesized. One of these molecules was decorated with four fullerenes via an aliphatic spacer. This is the sterically overcrowded compound with an octapodal morphology. The other star lacks the fullerenes and provides free space between the conjugated arms. This mesogen does not aggregate in solution, but in solid state it forms a hexagonal columnar and a highly ordered oblique helical columnar phase, while the octopus molecule assembles in an amorphous solid. Photophysical studies of the octapodal compound in solution and the solid thin film reveal the formation of J-type aggregates, in which the interaction between donors (porphyrin) and acceptors (fullerene) dominates leading to absorption bands in the NIR region of the spectra. The mixture of both compounds results in a self-assembly which is called the Click procedure. Fullerenes of the octopus nanosegregate in the pockets of the star mesogens generating hexagonal columnar structures with a regular stacking along the columnar axis. Thus providing free space is a tool to control the competition between supramolecular interactions and nanosegregation. Such liquid-crystalline donor-acceptor structures may play a role in future LC photovoltaic applications.

Enhanced Interfacial Modification by Ordered Discotic Liquid Crystals for Thermotolerance Perovskite Solar Cells.

Traditionally used phenylethylamine iodide (PEAI) and its derivatives, such as ortho-fluorine o-F-PEAI, in interfacial modification, are beneficial for perovskite solar cell (PSC) efficiency but vulnerable to heat stability above 85 °C due to ion migration. To address this issue, we propose a composite interface modification layer incorporating the discotic liquid crystal 2,3,6,7,10,11-hexa(pentoxy)triphenylene (HAT5) into o-F-PEAI. The triphenyl core in HAT5 promotes π-π stacking self-assembly and enhances its interaction with o-F-PEAI, forming an oriented columnar phase that improves hole extraction along the one-dimensional direction. HAT5 repairs structural defects in the interfacial layer and retains the layered structure to inhibit ion migration after annealing. Ultimately, our approach increases the efficiency of solar cells from 23.36% to 25.02%. The thermal stability of the devices retains 80.1% of their initial efficiency after aging at 85 °C for 1008 hours without encapsulation. Moreover, the optimized PSCs maintained their initial efficiency of 82.4% after aging under one sunlight exposure for 1008 hours. This study provides a novel strategy using composite materials for interface modification to enhance the thermal and light stability of semiconductor devices.

Enhanced Interfacial Modification by Ordered Discotic Liquid Crystals for Thermotolerance Perovskite Solar Cells

Traditionally used phenylethylamine iodide (PEAI) and its derivatives, such as ortho‐fluorine o‐F‐PEAI, in interfacial modification, are beneficial for perovskite solar cell (PSC) efficiency but vulnerable to heat stability above 85 °C due to ion migration. To address this issue, we propose a composite interface modification layer incorporating the discotic liquid crystal 2,3,6,7,10,11‐hexa(pentoxy)triphenylene (HAT5) into o‐F‐PEAI. The triphenyl core in HAT5 promotes π‐π stacking self‐assembly and enhances its interaction with o‐F‐PEAI, forming an oriented columnar phase that improves hole extraction along the one‐dimensional direction. HAT5 repairs structural defects in the interfacial layer and retains the layered structure to inhibit ion migration after annealing. Ultimately, our approach increases the efficiency of solar cells from 23.36% to 25.02%. The thermal stability of the devices retains 80.1% of their initial efficiency after aging at 85 °C for 1008 hours without encapsulation. Moreover, the optimized PSCs maintained their initial efficiency of 82.4% after aging under one sunlight exposure for 1008 hours. This study provides a novel strategy using composite materials for interface modification to enhance the thermal and light stability of semiconductor devices.

Oxacalix[4]arene functionalized macrocycle with columnar liquid crystal phase and self-assembly tuned by reversible photoisomerization process

Oxacalix[4]arene is a unique type of macrocyclic compound closely related to calixarenes. It consists of four aromatic rings connected by oxygen bridges. This molecule exhibits a remarkable blend of rigidity and flexibility, making it adaptable to various molecular interactions. In present study, we present our findings on the synthesis and characterization of four new supramolecular bowl-shaped materials (FOC1-FOC4) originating from the robust core structure of tetranitro oxacalix[4]arene. The thermal decomposition was analyzed through the thermogravimetric analysis. All four oxacalix[4]arene-based macrocycles adopted a 1,3-alternate (saddle-like) conformation and exhibited a columnar hexagonal phase with a behavior to self-assemble at room temperature. All four macrocycles (FOC1-FOC4) displayed enantiotropic mesophases within a temperature range of 56.0 °C to 63.0 °C. Further, the relationship between the molecular structure, particularly the varying alkyl chains, and the mesomorphic properties of these compounds was also examined. It was found that the mesomorphic behavior of FOC3 and FOC4 was significantly influenced by cis and trans isomerization. These two compounds exhibited photoswitching behavior, transitioning between their cis and trans forms when exposed to 365 nm light. Notably, they displayed a prolonged stability in the cis form after UV exposure, which is valuable for applications requiring precise control over the switching process.

Thermotropic "Plumber's Nightmare"-A Tight Liquid Organic Double Framework.

Gyroid, double diamond and the body-centred "Plumber's nightmare" are the three most common bicontinuous cubic phases in lyotropic liquid crystals and block copolymers. While the first two are also present in solvent-free thermotropics, the latter had never been found. Containing six-fold junctions, it was unlikely to form in the more common phases with rod-like cores normal to the network columns, where a maximum of four branches can join at a junction. The solution has therefore been sought in side-branched mesogens that lie in axial bundles joined at their ends by flexible "hinges". But for the tightly packed double framework, geometric models predicted that the side-chains should be very short. The true Plumber's nightmare reported here, using fluorescent dithienofluorenone rod-like mesogen, has been achieved with, indeed, no side chains at all, but with 6 flexible end-chains. Such molecules normally form columnar phases, but the key to converting a complex helical column-forming mesogen into a framework-forming one was the addition of just one methyl group to each pendant chain. A geometry-based explanation is given.

Thermotropic “Plumber’s Nightmare” ‐ A Tight Liquid Organic Double Framework

Gyroid, double diamond and the body‐centred “Plumber’s nightmare” are the three most common bicontinuous cubic phases in lyotropic liquid crystals and block copolymers. While the first two are also present in solvent‐free thermotropics, the latter had never been found. Containing six‐fold junctions, it was unlikely to form in the more common phases with rod‐like cores normal to the network columns, where a maximum of four branches can join at a junction. The solution has therefore been sought in side‐branched mesogens that lie in axial bundles joined at their ends by flexible “hinges”. But for the tightly packed double framework, geometric models predicted that the side‐chains should be very short. The true Plumber’s nightmare reported here, using fluorescent dithienofluorenone rod‐like mesogen, has been achieved with, indeed, no side chains at all, but with 6 flexible end‐chains. Such molecules normally form columnar phases, but the key to converting a complex helical column–forming mesogen into a framework‐forming one was the addition of just one methyl group to each pendant chain. A geometry‐based explanation is given.

Smart design of highly luminescent octupolar mesogenic tetra styryl-alkynyl bipyrimidine-based chromophores presenting non-linear optical properties

The research investigations reported in this paper focuses on the influence of rational design on the photophysical properties of new all-organic multifunctional chromophores. Nonlinear optical (NLO) behavior, optical properties and mesogenicity of several new π-conjugated octupolar chromophores, presenting alkoxy styryl-alkynyl donor groups carrying aliphatic achiral and chiral chains in the 3,4/3,5/2,4 position, connected to electron-accepting 2,2-bipyrimidine cores are investigated by various techniques (light-transmission measurements, polarized-light optical microscopy, differential scanning calorimetry measurements, two-photon excited fluorescence and Hyper Rayleigh Scattering). The mesogenic properties were investigated depending on the position of the alkoxy chain and the 3,4 derivatives were found to exhibit liquid-crystal properties with the formation columnar phases over large temperature ranges which were confirmed by small-angle X-ray scattering analysis. All the molecules exhibit exceptional high fluorescence quantum yields values around 80 % and excellent nonlinear optical properties.

Triphenylene diimides: A new class of discotic liquid crystals

Unlike the well-explored perylene diimides and naphthalene diimides, the synthesis and characterization of triphenylene diimides have not been reported to date. In this study, several di(decyloxy)-substituted triphenylene 2,3,6,7-tetracarboxyldiimides with various imide substituents were synthesized and comprehensively analyzed for their photochemical properties and mesophase behavior. It was observed that different imide substituents significantly affect self-assembly in both solution and the liquid-crystalline state. Specifically, diimide 2–1, with two n-octyl chains at the imide nitrogens, exhibits a tendency to self-assembly at relatively high concentrations in CDCl3 and displays a hexagonal columnar (Colh) phase near room temperature. Remarkably, its isomer, diimide 2–2, with two branched 2-ethylhexyl chains, exhibits an enatiotropic Colh phase with an unusually large range of 292 °C, extending from 7 °C to 299 °C. Furthermore, the study also reports two triphenylene monoimide diesters as room temperature liquid crystals, each composed of one imide, two alkoxycarbonyl, and two alkoxy side chains. These findings not only enrich the diversity of aromatic diimides but also highlight the potential applications of these novel diimides in the field of liquid crystals.

Interface strengthening mechanism of TZM/Q235 joint by ultrasonic-assisted electron beam welding with high entropy alloy interlayer

The high-strength joints of TZM/CoCrFeNiMo0.2/Q235 were realized by ultrasonic-assisted electron beam welding. The effects of ultrasonic vibration on the microstructure evolution and mechanical properties of the reaction layers were analyzed. A reaction layer with a thickness of >10 μm was observed at the TZM side region. The reaction layer was characterized by columnar Fe2Mo phases growing perpendicular to the fusion line and FCC solid solutions with different grain orientations. Under the action of ultrasonic vibration, the eutectic structure of Fe2Mo phases and FCC solid solutions was evenly distributed in the reaction layer, and the grain orientation of the FCC solid solutions in the reaction layer changed to be the same as that in the fusion zone. Compared with the joint without ultrasonic vibration, the difference of nanoindentation hardness between the Fe2Mo phases and FCC solid solutions and the residual stress inside the reaction layer of the welding joint with an ultrasonic power of 80 W were significantly reduced. The maximum tensile strength of the joints was 318.4 ± 26 MPa, which was 18.9% higher than that of the joint without ultrasonic vibration.

Carrier transport and mesomorphic properties of deformable fluorinated perylene bisimide bearing disiloxane chains

We synthesized liquid crystalline difluorinated perylene bisimide derivatives bearing oligosiloxane moieties. At room temperature, these compounds exhibited columnar phases which were stabilized thermodynamically, compared to that of a non-fluorinated analog. The absorption bands in the thin films of the fluorinated compounds exhibited a slight bathochromic shift compared to that in the solution state, indicating a weak electronic coupling between the fluorinated perylene bisimide cores in the columnar phases. The electron mobilities in the columnar phases of the difluorinated compounds were determined to be on the order of 10−2 cm2V−1s−1 at room temperature by the time-of-flight measurements. The LUMO levels of the difluorinated compounds were lowered by 0.1 eV from that of non-fluorinated analog. Anion radicals of the fluorinated compounds were stable as that of the non-fluorinated analog while dianions of the fluorinated compounds were unstable unlike that of the non-fluorinated analog. The difluorinated compounds was soft waxy solid. In particular, the 1,7-difluorinated derivative is deformable to form various shapes at room temperature. A study on the surface morphology of the thin film indicated formation of microscopic grooves, which should enhance the softness of the compound.

Mesomorphism, high-contrast negative fluorosolvatochromism and photoinduced fluorescence conversion of thienylcyanostyrene-pyridinium salts

Novel thienylcyanostyrene and pyridinium-based luminescent ionic liquid crystals (ILCs) characterized with different length of N-alkyl chains (N–C3H7 and N–C8H17) and different size of counter anions (Br−, BF4−, PF6− and Tf2N−) on pyridinium moiety have been synthesized. The chemical modifications of N-alkyl chains and counter anions are easily achieved via pyridine alkylation followed with further ion exchanges, which played a key role in tuning supramolecular self-assembly of these ILCs. The compounds with shorter N–C3 alkyl chain (E-CTPC3X, X = Br−, BF4−, PF6− and Tf2N−) can self-assemble into 3D cubic phase or 2D hexagonal columnar phase depending on the size of counter anion, while the analogues with longer N–C8 alkyl chain (E-CTPC8X, X = BF4− and Tf2N−) only result smectic A phases. Moreover, the prolongation of the N-alkyl chain or enlargement of counter anion could significantly decrease the clear points of LC phases avoiding the thermal decomposition at high temperature, whereas introducing counter anions such as BF4−, PF6− that can form hydrogen bonds have stabilized the LC phases. The notable negative fluorosolvatochromism and the photoinduced fluorescence conversion with high-contrast of these ILCs were observed using UV–vis absorption and photoluminescence (PL) spectra, and was further analyzed by dynamic 1H NMR. These ILCs had been used as dopant to modify the n-Si/PEDOT:PSS heterojunction solar cells (HSCs) with 2 fold hole mobility (μhole) enhancement of the PEDOT:PSS layer.

Dynamic Dipole Moment of Luminescent Liquid Crystals Enabled Highly Efficient Active Waveguide Materials Design and Synthesis

AbstractOrganic optical waveguide materials have attracted considerable attention for their promising applications in photonic and optoelectronic devices. However, for most materials, excellent light‐loss properties at high temperature cannot be obtained due to many factors. Consequently, realizing efficient optical waveguide materials that perform well at elevated temperatures remains a significant challenge. In this study, relying on the luminescent properties and self‐assembly properties of luminescent liquid crystals (LLCs), successfully fabricated materials are present for highly efficient active optical waveguides. A systematically synthesized set of LLCs with different structures is named according to the substituent type and the position of the cyano group, namely α‐DECN, α‐DEEOCN, β‐DECN, and β‐DEEOCN. Notably, α‐DECN and β‐DECN reveal hexagonal columnar phase, while α‐DEEOCN and β‐DEEOCN exhibit smectic phase. Optical waveguide experiments have revealed that the obtained LLCs showed highly efficient optical waveguide behavior, where the lowest light loss reached 0.15 dB mm−1 at room temperature. Remarkably, these LLCs show even lower light loss at high temperatures, with the light loss reaching 0.11 dB mm−1 as the lowest point. Further experimental results indicate that this phenomenon is attributed to the change in the dipole moment of these molecules. This research forms a significant groundwork for advanced exploration in optical waveguide material.

Simulating the Lyotropic Phase Behavior of a Partially Self-Complementary DNA Tetramer.

DNA oligomers in solution have been found to develop liquid crystal phases via a hierarchical process that involves Watson-Crick base pairing, supramolecular assembly into columns of duplexes, and long-range ordering. The multiscale nature of this phenomenon makes it difficult to quantitatively describe and assess the importance of the various contributions, particularly for very short strands. We performed molecular dynamics simulations based on the coarse-grained oxDNA model, aiming to depict all of the assembly processes involved and the phase behavior of solutions of the DNA GCCG tetramers. We find good quantitative matching to experimental data at both levels of molecular association (thermal melting) and collective ordering (phase diagram). We characterize the isotropic state and the low-density nematic and high-density columnar liquid crystal phases in terms of molecular order, size of aggregates, and structure, together with their effects on diffusivity processes. We observe a cooperative aggregation mechanism in which the formation of dimers is less thermodynamically favored than the formation of longer aggregates.

Current Trends in Liquid Crystal Polymers and Their Applications: A Review

Liquid crystal polymers (LCPs) are now highly focused by researchers due to their improved thermal properties, mechanical strength, excellent dielectric strength, resistance to solvents, better dimensional stability, and gas barrier properties. LCPs can be used in valuable widespread applications such as energy storage, high-performance polymer fibers, actuators, information technologies, surface modification, shape memory materials, data storage, fiber optics, the medical field, electrical or electronics devices, aircraft, chemical, domestic equipment, ultra-high-strength fibers, biosensing, advanced communication systems, satellite systems, biosensing, bio-oscillators, and bioprocess monitoring. LCPs can self-assemble into different liquid crystalline phases like nematic, cholesteric, smectic, and columnar phases. The self-assembling structures of LCPs can be affected by the chemical and structural structures of the backbone of the polymeric material, nearby alkyl tails, mesogenic units, flexible spacers, etc. Depending on the mesogenic units in their molecular architecture, LCPs are basically classified into various categories, such as crosslinked, main chain, and sidechain. Again, they are also classified as cholesteric, nematic, and smectic mesophases. This paper provides a fundamental understanding, an informative overview, and details of structural aspects, properties, classification, commercial aspects, and applications of LCPs.