Search

Mechanical stretching is commonly used for mesogen alignment which is essential for the muscle-like actuations of liquid crystal elastomers (LCEs). Despite the simplicity of the method, the mesogens are typically aligned in the stretching direction, limiting exclusively the LCE to an actuation mode of cooling-induced elongation. Here, we design an interpenetrating double network consisting of an LCE network and an elastomer network, with one polymerized network stretched before the polymerization of the other network. Depending on the polymerization sequence of the two networks, the double network shows two opposite actuation modes, namely, the conventional cooling-induced elongation or an unusual cooling-induced contraction. Strategic integration of the two opposite behaviors into the same LCE leads to sophisticated actuation difficult to achieve with a conventional LCE design. Coupled with 3D printing, geometrically complexed LCEs with diverse multimodal four-dimensional actuation behaviors are illustrated. Our work expands the design scope of LCE actuators and their potential device applications. [ABSTRACT FROM AUTHOR]

Liquid crystals, which have both liquid and solid properties, inevitably exhibit fluctuations. Some frustrated liquid-crystalline phases with a hierarchical structure, such as cybotactic nematic, modulated smectic, and bicontinuous cubic phases, are fascinating fluctuation-induced phases. In addition to these equilibrium phases, a pattern formation that is a nonequilibrium order through fluctuation is one of the most attractive research areas in soft matter. In this review, the studies on producing these fluctuation-induced orders in liquid crystals are described. Liquid-crystalline supermolecules in which several mesogens are connected via a flexible spacer have been designed. They have not only a characteristic shape but also an intra-molecular dynamic order. The supermolecules induce the fluctuations in layer structures at a molecular level, producing from the frustrated hierarchical to dynamic dissipative structures. In addition to reviewing molecular design for the hierarchical structures, the pattern propagation in a smectic phase is discussed based on the rotation of smectic blocks through Rayleigh–Bénard convection. [ABSTRACT FROM AUTHOR]

This study focuses on the helical conformation of the main chain of syndiotactic poly(substituted methylene)s with 4‐cyanobiphenyl (CB) moieties incorporated at the ends of the alkyloxycarbonyl side chains. The polymers are designated as PCBn, where n is the number of methylene units in the spacer between the main chain and CB. PCB6 and PCB8 assemble the side chains into layers without positional order within the layers. Meanwhile, PCB10 and PCB12 assemble the side chains into layers with a short‐range positional order. Each CB moiety at a side chain end is bonded to a carbon atom, which is arranged along the helical main chain contour, and its position correlates with that of the carbon atom. As the temperature increases, PCB10 undergoes a phase transition, losing the positional order of the side chains within a layer, which alters the main chain conformation. Consequently, the positions of the side‐chain CB moieties affect the helical conformation of the main chain. In contrast, PCB12 maintains the main chain conformation when undergoing a phase transition similar to that of PCB10. PCB12 with the longer spacer allows the main chain to adopt a helix conformation, which is independent of the positions of side‐chain CB moieties. [ABSTRACT FROM AUTHOR]

Mesogens, which are typically stiff rodlike or disklike molecules, are able to self-organize into liquid crystal (LC) phases in a certain temperature range. Such mesogens, or LC groups, can be attached to polymer chains in various configurations including within the backbone (main-chain LC polymers) or at the ends of side-chains attached to the backbone in an end-on or side-on configuration (side-chain LC polymers or SCLCPs), which can display synergistic properties arising from both their LC and polymeric character. At lower temperatures, chain conformations may be significantly altered due to the mesoscale LC ordering; thus, when heated from the LC ordered state through the LC to isotropic phase transition, the chains return from a more stretched to a more random coil conformation. This can cause macroscopic shape changes, which depend significantly on the type of LC attachment and other architectural properties of the polymer. Here, to study the structure–property relationships for SCLCPs with a range of different architectures, we develop a coarse-grained model that includes torsional potentials along with LC interactions of a Gay–Berne form. We create systems of different side-chain lengths, chain stiffnesses, and LC attachment types and track their structural properties as a function of temperature. Our modeled systems indeed form a variety of well-organized mesophase structures at low temperatures, and we predict higher LC-to-isotropic transition temperatures for the end-on side-chain systems than for analogous side-on side-chain systems. Understanding these phase transitions and their dependence on polymer architecture can be useful in designing materials with reversible and controllable deformations. [ABSTRACT FROM AUTHOR]

Copyright of Paint & Coatings Industry (0253-4312) is the property of Paint & Coatings Industry Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The liquid crystal state (LC) in polymer chemistry is a topic discussed in varied materials research. The anisotropic properties typical of these compounds are mostly the result of the presence of mesogens in the structure of liquid crystals. This article traces the development of liquid crystal science, focusing on liquid crystal epoxy resins (LCERs) and emphasizing the crucial role of mesogens and their diverse effect on the materials. It also highlights the importance of understanding the morphology of LC polymers, explaining their profound impact on material properties and performance. It explores the cross-linking process of liquid crystal resins and composites, describing how changes in structural factors affect material structure. The article also provides information about hardeners and their influence on the cross-linked structure. Various nanofillers were also discussed, elucidating their impact on the resulting composites. [ABSTRACT FROM AUTHOR]

Solution-state self-assemblies of block copolymers to form nanostructures are tremendously attractive for their tailorable morphologies and functionalities. While incorporating moieties with strong ordering effects may introduce highly orientational control over the molecular packing and dictate assembly behaviors, subtle and delicate driving forces can yield slower kinetics to reveal manifold metastable morphologies. Herein, we report the unusually convoluted self-assembly behaviors of a liquid crystalline block copolymer bearing triphenylene discotic mesogens. They undergo unusual multiple morphological transitions spontaneously, driven by their intrinsic subtle liquid crystalline ordering effect. Meanwhile, liquid crystalline orderedness can also be built very quickly by doping the mesogens with small-molecule dopants, and the morphological transitions are dramatically accelerated and various exotic micelles are produced. Surprisingly, with high doping levels, the self-assembly mechanism of this block copolymer is completely changed from intramolecular chain shuffling and rearrangement to nucleation-growth mode, based on which self-seeding experiments can be conducted to produce highly uniform fibrils. Assembly of block copolymers can be controlled to give varying morphologies and functionalities, but there are still aspects of the process that are not well understood. Here, the authors report convoluted self-assembly behaviours of block copolymers with discotic liquid crystalline moieties. [ABSTRACT FROM AUTHOR]

Recently, a large family of at least 14 discotic liquid crystals was discovered that are exceptions to the conventional paradigm that discotic mesogens tend to feature long, flexible tails on their periphery. To understand why these materials are liquid crystals, as well as the structural determinants of discotic phase behavior, we studied a group of closely related small tail-free disk-like molecules, including both mesogenic and non-mesogenic compounds differing only in the position of a single fluorine substituent. The rigidity and structural simplicity of these molecules make them well suited to for study by large, fully all-atom simulations. Using a combination of static and dynamic metrics, we were able to identify several key features of the columnar mesophase and, thereby, conclusively identify a columnar liquid crystalline mesophase present in a subset of our systems. Our simulations feature molecules hopping between columns in the columnar mesophase and distinctive molecular rotations in 60° steps about the columnar axis. The ability to create and characterize columnar mesophases in silico provides a potent tool for untangling the structural determinants of liquid crystalline behavior in these and other tail-free discotic liquid crystals. [ABSTRACT FROM AUTHOR]

A novel homologous series of cinnamoyl ester comprising of elven (C1 to C16) homologues liquid crystal (LC) samples have been synthesized and characterized using instrumental methods (spectral and thermal) of analysis and DFT approach. As results, middle ordered melting type of series with exhibition of nematic mesophase were observed. The observed mesogenic properties and transition temperature are affected by the size of alkyl chains that shows mesomorphism is susceptible to molecular structure. The prepared LCs of cinnamoyl ester derivatives were further examined for their biological activities and the obtained results indicates a good biological potential for the studied LC materials. [ABSTRACT FROM AUTHOR]

Liquid crystalline nanoparticles (LC NPs) are a kind of polymer NPs with LC mesogens, which can form special anisotropic morphologies due to the influence of LC ordering. Owing to the stimuli‐responsiveness of the LC blocks, LC NPs show abundant morphology evolution behaviors in response to external regulation. LC NPs have great application potential in nano‐devices, drug delivery, special fibers and other fields. Polymerization‐induced self‐assembly (PISA) method can synthesize LC NPs at high solid content, reducing the harsh demand for reaction solvent of the LC polymers, being a better choice for large‐scale production. In this review, we introduced recent research progress of PISA‐LC NPs by dividing them into several parts according to the LC mesogen, and discussed the improvement of experimental conditions and the potential application of these polymers. [ABSTRACT FROM AUTHOR]

The recent identification of ferroelectricity within the nematic phase of liquid crystals has triggered significant interest. However, prior to this discovery; the potential existence of ferroelectricity in the nematic phase had already been investigated in the context of cybotactic nematic phases of liquid crystals. Ferroelectricity has previously been reported in chiral and achiral smectic phases. While the presence of nano-sized smectic clusters in the nematic phase of rod-shaped molecules, termed as cybotactic nematic, was recognised, it did not earn substantial attention. However, the cybotactic nematic phase in bent-core mesogens has gained significant attention due to its unconventional ferroelectric-like behaviour. To link the recent advancements in understanding ferroelectricity in the nematic phase, a comprehensive review has been conducted on the cybotactic nematic phase. This review encompasses a foundational explanation of the cybotactic model, followed by an overview of cybotactic phases in rod-shaped mesogens. The central focus lies in evaluating cybotactic phases within bent-core nematic systems, covering early debates, fundamental experimental evidences, and a compilation of mesogens that exhibit the cybotactic nematic phase. Furthermore, the review describes into the physical attributes of mesogens featuring cybotactic nematic phases, including discussions on repolarisation, dielectric properties, and optical characteristics. [ABSTRACT FROM AUTHOR]

To develop smart ionic skins capable of multi‐responsiveness and switchable ionic conductivity, a stimuli‐responsive and ionic conductive azobenzene‐based monomer is newly synthesized, uniaxially oriented, and polymerized for anisotropic liquid crystal elastomers (LCEs). Since the uniaxially oriented monodomain LCE with ionic asymmetric azobenzene monomers (i‐AAM) is prepared by thermal oligomerization, uniaxial stretching, and subsequent photopolymerization, the stimuli‐responsive i‐AAM LCE is thermally contracted by increasing the temperature above TNI as well as is bent along the aligned direction by irradiating it with UV light. In addition to the change of shape, the ionic conductivity of the LCE is reversible in response to heat and light stimuli. Polydomain i‐AAM LCE polymerized without the stretching process exhibits higher ionic conductivity than stretched monodomain LCE due to the initially formed stable ionic pathways. Ionic conductivity can also be switched simultaneously by polarity changes in response to the photoisomerization of i‐AAM, increased mobility from heat, and an elastic mechanoresponse from external stresses. These i‐AAM LCE‐based soft grippers exhibit stimuli‐responsive grasping and releasing actuation and detect ionic conductivity switches finely, suggesting potential as smart skins for advanced soft robots. [ABSTRACT FROM AUTHOR]

First series of fluorescein-based hexacatenar mesogens consisting of a central fluorescein unit and two 1,2,3-triazole dendritic wings were designed and synthesized by using the Williamson reaction and Cu-assisted alkyne-azide cycloaddition reaction. Polarized optical microscopy textures, differential scanning calorimetry curves, and X-ray diffraction (XRD) data demonstrated that all the compounds can self-assemble into hexagonal columnar mesophases. Organogel test demonstrated that these compounds could form organogel in some moderate polar solvents with irregularly winkled morphologies. Density functional theory calculation demonstrated that these mesogens adopted distorted conformation which might be the reason why narrow mesogenic temperature ranges and irregularly winkled morphologies in these compounds are observed. [ABSTRACT FROM AUTHOR]

We have designed new chiral smectic mesogens with the -CH2O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics. [ABSTRACT FROM AUTHOR]

Synthesis of a new series of mesogenic dimers and investigation of their liquid crystalline properties with thermal, optical and XRD methods is reported. Unlike dimeric mesogens studied to date, the presently reported dimers are derived from a single-ring mesogen containing a partially fluorinated dodecyl chain, which effects nanosegregation and formation of a lamellar phase. The reported four diesters with the odd-membered connecting alkyl chain exhibit a SmA phase. In contrast, two even-membered analogues have higher melting points and do not exhibit mesogenic behaviour. [ABSTRACT FROM AUTHOR]

Three homologous series of 3‑hydroxy-4-(((-4-benzoxazol-2-yl)phenyl)imino)methyl)phenyl-4-alkoxybenzoate (with ester linkage) and 5-(alkoxy)-2-(((4-(5-benzoxazol-2-yl)phenyl)imino)methylphenol (without ester linkage) Schiff based derivatives, bearing different substituents at 5 position i.e., 5-methylbenzoxazole, benzoxazole and 5-chlorobenzoxazole units at the end of the molecule and their Copper complexes were synthesised. The molecular structure of all the compounds were elucidated by different spectroscopic techniques such as FT-IR, 1H & 13C NMR and mass spectrometry together with elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The structure-property relationships, compounds bearing a variety of polar substituents and changing the spacer from ester linked to without ester-linked has been studied. Substituents with stronger electron-withdrawing properties gave a wider mesomorphic temperature domain, in the order Cl > CH3 >H.

This work presents the synthesis and self-organization of the calamitic fluorinated mesogen, 1,1,2,2–tetrafluoro–2–(1,1,2,2–tetrafluoro–4–iodobutoxy)ethanesulfonic acid, a potential model for perfluorosulfonic acid membranes (PFSA). The compound is derived in three steps from 1,1,2,2–tetrafluoro–2–(1,1,2,2–tetrafluoro–2–iodoethoxy)ethanesulfonyl fluoride, achieving a 78% overall yield. The resulting compound exhibits intricate thermal behavior. At 150 °C, a crystal-to-crystal transition is observed due to the partial disordering of calamitic molecules, which is followed by isotropization at 218 °C. Upon cooling, sample ordering occurs through the formation of large smectic liquid crystalline phase domains. This thermotropic state transforms into a layered crystal phase at lower temperatures, characterized by alternating hydrophilic and hydrophobic layers. Using X-ray diffraction, crystalline unit cell models at both room temperature and 170 °C were proposed. Computer simulations of the molecule across varying temperatures support the idea that thermal transitions correlate with a loss of molecular orientation. Importantly, the study underscores the pivotal role of precursor self-organization in aligning channels during membrane fabrication, ensuring controlled and oriented positioning. [ABSTRACT FROM AUTHOR]

The steroidal derivatives have been found to be extremely good mesogens since their origin. Due to their inherent chirality, they have the potential to induce a wide variety of liquid crystalline phases, including frustrated phases, depending on the structure of the steroidal skeleton and the substituents attached. In this report, thirteen new homologous Schiff's base derivatives were synthesised by condensing 4-n-alkoxy aniline with 4-formyl phenyl cholesteryl carbonate. All the compounds were characterised using elemental analysis, FT-IR, 1H-NMR and 13C-NMR. In order to study the liquid crystalline behaviour of the synthesised compounds, optical texture studies were carried out using polarising optical microscope in heating and cooling cycles. The derivatives showed a variety of mesophases, including chiral nematic (N*), twist grain boundary-A (TGBA), smectic A (SmA) and chiral smectic C (SmC*) phases. The thermal behaviour was determined using a differential scanning calorimeter and thermogravimetric analysis. All the synthesised compounds are UV-active and show photoluminescence in the blue emission region with good quantum yield. [ABSTRACT FROM AUTHOR]

The present investigation focuses on the geometrical optimized parameters, IR and raman activity based on vibrational frequencies, and global reactivity descriptors of mesogens namely; para-azoxyanisole (PAA), ethyl para-azoxybenzoate (EPAB) and non-mesogen biphenyl-4-carboxylic acid (BCA) molecules via the Density functional theory (DFT) and Hartree–Fock (HF) technique accompanied with 6–31++G (d, p) basis set. The wavenumbers/frequencies obtained for utmost of the vibrational modes are in the predicted range but with minimal error. Reactivity of these molecules based on the molecular properties viz., HOMO, LUMO energies, ionization potential, electro negativity, chemical potential, electron affinity, chemical hardness, and softness has also been focused. The DFT method considers all different electronic interactions thereby give accurate results as compared to Hartree–Fock method. The azoxy bond plays an important role in chemical bond formation in liquid crystals, chemical intermediates, process control, and pharmaceuticals etc. Further, the estimated band gap values indicate the understanding of fine tuning mechanism for exploring the possible industrial applications. [ABSTRACT FROM AUTHOR]

A systematic study of a binary system composed of 4-n-pentyl 4′-cyanobiphenyl (5CB) and 4-n-pentyl phenyl 4-n′-hexyloxy benzoate (ME6O.5) mesogens showing an induced smectic A at different molar concentrations has been done. Heat capacity and optical birefringence measurements have been performed around the N-SmA phase transition region. The heat capacity peaks could be fitted well below the N-SmA transition by means of an extended Landau mean-field model. The first-order nature of the transition throughout the composition range can be inferred. This transition is rather close to the tricritical point when the nematic range is sufficiently increased. The latent heat decreases with the increase in the nematic range. For large nematic range, the latent heat drops to zero and the heat capacity peak associated with N-SmA phase transition disappear, contrary to previously reported most of the usual N-SmA phase transition. Precision birefringence measurements also agree well with the heat capacity data. [ABSTRACT FROM AUTHOR]

Using a thermodynamic model developed by us to study the structural and electro-optical properties of ${\rm Sm\; C}_{\rm A}^{\rm \ast }$ Sm C A ∗ phase, we investigate the temperature dependence of helical pitch, tilt angle and spontaneous polarization of a homologous series of fluorinated biphenyl benzoate esters (3FnHBM6, n = 2, 5, 7) and one of the series W-316-3 obtained from the mixture of two chiral liquid crystalline compounds 6F2OBi and 3F6HBM6. The free-energy density of the system exhibiting ${\rm Sm\; C}_{\rm A}^{\rm \ast }$ Sm C A ∗ phase is written as an expansion series in terms of all the relevant degrees of freedom: ${\bf Q}_{{\bf ij}}$ Q i j , ψ, P, q and the resulting coupling terms between these order parameters. The values of Landau coefficients are determined from the experimental data of antiferroelectric mesogens 3FnHBM6 (n = 2, 5, 7) and W-316-3 in the ${\rm Sm}\; {\rm C}_{\rm A}^{\rm \ast }$ Sm C A ∗ phase. Using these coefficients, the electro-optical and structural properties have been studied. We have found good agreements between the theoretical and experimental results. [ABSTRACT FROM AUTHOR]

Chemical, optical, and thermal characterization are carried out for seven hydrogen bond thermotropic liquid crystalline complexes formed between pentyloxy benzoic acid (5BAO) and p-n-alkyl benzoic acids (nBA, where n refers alkyl carbon chain length which varies from ethyl to octyl. FTIR, ¹H, and 13C Nuclear Magnetic Resonance (NMR) establishes the chemical investigations. Nematic and smectic F are the mesophases observed. Polarizing Optical Microscopic (POM) studies ensures the mesophases identified. Thermal investigation using Differential Scanning Calorimeter (DSC), provides the phase transition temperatures, enthalpy values, thermal stability factor, specific heat capacity values, and thermal equilibrium of the mesogenic complexes. [ABSTRACT FROM AUTHOR]

Antiferroelectricity is a desirable property of liquid crystalline materials. Therefore, we synthesised and studied two new chiral rod-like mesogens with a molecular core based on two biphenyls connected via ester linkage, with the phenyl substituted by a fluorine atom. The studied mesogens are characterised by nuclear magnetic resonance spectroscopy and mass spectrometry analysis. They have methyl heptyl in the chiral chain and exhibit an antiferroelectric phase in a very broad temperature range. We investigated their mesomorphic properties and confirmed the phase identification by differential scanning calorimetry and broad-frequency dielectric spectroscopy measurements. Additionally, we compared the studied mesogens with previously synthesised analogous materials. Two mixtures were formulated using a base mixture and new mesogens. The helical pitch of the synthesised mesogens and formulated mixtures was estimated using the selective reflection method. [ABSTRACT FROM AUTHOR]

Structurally simple two rod-like mesogens with a three-ring core consisting of biphenyl and phenyl rings are synthesised to investigate the mesophase properties, molecular organisation and the orientational order parameter. In mesogen-1, a dodecyloxy terminal chain is present on the biphenyl ring while the phenyl ring is free from substituent. For mesogen-2, in addition to the dodecyloxy chain, the butyl chain is placed on the phenyl ring. The Hot-stage optical polarising microscopy (HOPM) and differential scanning calorimetry (DSC) measurements show smectic A (SmA), smectic B (SmB), and crystal E (CryE) phases for mesogen-1 and SmA, smectic C (SmC) and smectic F (SmF) phases for mesogen-2. The presence of smectic mesophases is established by X-ray Diffraction (XRD). 1D and 2D 13C solid-state NMR experiments are performed in smectic mesophases to find the orientational order parameters of the phenyl rings of the core. The main order parameter (Szz) of the mesogens in the SmB and SmF phase is in the range of 0.87–0.93. The excellent spectral resolution noticed in 13C NMR spectra in the SmB mesophase (mesogen-1) indicates that the internal rotations of the molecules along the long axis are primarily unhindered. [ABSTRACT FROM AUTHOR]

Spiropyran (SP) based mechanochromic systems are intensively interesting in the research area of mechanochromic materials. Herein, an SP mechanophore is chemically incorporated into a liquid crystalline elastomer (LCE) network through Michael addition. The rigidity of mesogens and the orientation of polymer main chains, in which the aligned mesogens and SP moieties are covalently attached, facilitate the transduction of applied force to SP mechanophore to trigger mechanochromic reaction. The LCE network provides enough elasticity for mechanochromic activation. The obtained SP‐LCEs demonstrate strong and reversible mechanochromic response upon mechanical compression. The mechanochromic efficiency and sensitivity are substantially enhanced by doping the SP‐LCE matrix with nano zinc oxide such that it is easy to write on the material surface by using a thin iron wire. The authors hope such SP‐LCE materials will be further developed for real‐time stress detection applications. [ABSTRACT FROM AUTHOR]

In this work, we aim to model the reorientation process of mesogens in nematic liquid crystal elastomers within the context of dynamics. We consider a continuum model with separate mappings for the deformation of the monolithic material and the orientation of the nematic director, where the latter describes the inclination of the mesogens. We achieve the inextensibility of the nematic director through the introduction of drilling degrees of freedom. We combine this approach with the application of the principle of virtual power and a mixed finite element formulation, in order to formulate distinct momentum and angular momentum balance laws for the two separate mappings. Furthermore, we include in our continuum model a volume load and a surface load associated only with the orientation mapping. We show in the presented three numerical examples that our formulation enables the fulfillment of all momentum and angular momentum balance laws. [ABSTRACT FROM AUTHOR]

Previous theoretical studies of calamitic (i.e., rod-like) ionic liquid crystals (ILCs) based on an effective one-species model led to indications of a novel smectic-A phase with a layer spacing being much larger than the length of the mesogenic (i.e., liquid–crystal forming) ions. In order to rule out the possibility that this wide smectic-A phase is merely an artifact caused by the one-species approximation, we investigate an extension that accounts explicitly for cations and anions in ILCs. Our present findings, obtained by grand canonical Monte Carlo simulations, show that the phase transitions between the isotropic and the smectic-A phases of the cation–anion system are in qualitative agreement with the effective one-species model used in the preceding studies. In particular, for ILCs with mesogens (i.e., liquid–crystal forming species) carrying charged sites at their tips, the wide smectic-A phase forms, at low temperatures and within an intermediate density range, in between the isotropic and hexagonal crystal phases. We find that in the ordinary smectic-A phase, the spatial distribution of the counterions of the mesogens is approximately uniform, whereas in the wide smectic-A phase, the small counterions accumulate in between the smectic layers. Due to this phenomenology, the wide smectic-A phase could be interesting for applications, which hinge on the presence of conductivity channels for mobile ions. [ABSTRACT FROM AUTHOR]

A number of wedge-shaped amphiphilic mesogens, derivatives of 1,2,3-tris(dodecyloxy)-benzene, which are precursors of polymer ion conducting membranes, were synthesized. The synthesized compounds included asymmetric 2,3,4-tris(dodecyloxy)benzenesulfonic acid and its sodium and pyridine salts. The self-organization processes of the synthesized mesogens were studied in thin films at different temperatures. Thermotropic liquid crystalline properties of these compounds were studied by DSC method. The structure of the liquid crystalline phases was studied using polarized thermooptical microscopy and X-ray diffraction. The influence of an orientation of magnetic field vector on phase composition of thin films was analyzed. It was shown that the texture of mesogenic films containing different counterions can be controlled by a combination of heating and applying a magnetic field. [ABSTRACT FROM AUTHOR]

Short, partially complementary, single-stranded (ss)DNA strands can form nanostructures with a wide variety of shapes and mechanical properties. It is well known that semiflexible, linear dsDNA can undergo an isotropic to nematic (IN) phase transition and that sufficiently bent structures can form a biaxial nematic phase. Here, we use numerical simulations to explore how the phase behavior of linear DNA constructs changes as we tune the mechanical properties of the constituent DNA by changing the nucleotide sequence. The IN-phase transition can be suppressed in so-called DNA "nunchakus": structures consisting of two rigid dsDNA arms, separated by a sufficiently flexible spacer. In this paper, we use simulations to explore what phase behavior to expect for different linear DNA constructs. To this end, we first performed numerical simulations exploring the structural properties of a number of different DNA oligonucleotides using the oxDNA package. We then used the structural information generated in the oxDNA simulations to construct more coarse-grained models of the rod-like, bent-core, and nunchaku DNA. These coarse-grained models were used to explore the phase behavior of suspensions of the various DNA constructs. The approach explored in this paper makes it possible to "design" the phase behavior of DNA constructs by a suitable choice of the constituent nucleotide sequence. [ABSTRACT FROM AUTHOR]

In this study, novel achiral mesogens containing 4,4'-biphenyl central core connected on both sides through an ester function to 1-(4-(alkyloxy)phenyl)-1 H-[1,2,3]-triazolyl group have been synthesised and characterised. Different mesophases have been identified, with the appearance of both a periodic striped pattern and propeller-patterned droplets close to the transition between the nematic and the smectic-C phases. This periodic texture has been found to be independent of the geometry of the sample cell. These observations suggest a spontaneous symmetry breaking, which can result either from an intrinsic enantioselective self-sorting process with a chirality synchronisation mechanism, or from an extrinsic surface mechanism at the interface between the two phases. [ABSTRACT FROM AUTHOR]

Triphenylene-based pentaalkynylbenzene dyads and naphthophenanthridine derivativediscotic mesogens have been proven a backbone-like utility for modern optoelectronic applications. Herein, we present the charge transport and organic electronic applications of naphthophenanthridine derivatives and a dimer composed of pentaalkynylbenzene (PA) and triphenylene (TP) discotic liquid crystals (DLCs). Naphthophenanthridine derivatives exhibit a hexagonal columnar (Colh) phase; whereas, triphenylene-pentaalkynylbenzene dyads show a columnar centred rectangular (Colr) phase and transform into Colh phase on doping the pure compounds with an electron-acceptor 2,4,7-trinitrofluorenone (TNF) in a 2:1 TNF/compound ratio. The ambipolar charge transport behaviour of the compounds mentioned above has been investigated by the time-of-flight technique. Naphthophenanthridine derivative renders an ambipolar charge transport, showing temperature-independent electron and hole mobility of the order of 3 × 10−4 cm2/Vs; whereas, TP-PA dimer yields an ambipolar charge carrier mobility of order 10−3 cm2/Vs. The phenazine-fused triphenylene DLC shows unipolar hole mobility of the order of 10−4 cm2/Vs; whereas, hydrogen-bonded Hpz-C9-TP DLCs exhibit ambipolar charge mobility of the order of 10−2 cm2/Vs. The high ambipolar charge carrier mobility in the investigated DLC compounds makes them suitable for fabricating organic semiconducting electronic devices. [ABSTRACT FROM AUTHOR]

Columnar mesogens constitute a fascinating class of supramolecular nano‐architectures owing to the exceptional properties induced by their self‐assembling behavior. Extending the π‐conjugated core in such systems by incorporating heteroatoms extensively influences their mesomorphic, photophysical properties, etc., presenting them as potential candidates for optoelectronic applications. In the present work, a series of novel nitrogen and oxygen‐incorporated chromenonaphthophenanthridine‐based elliptical dimers have been synthesized through tandem Pictet‐Spengler cyclization followed by ipso‐aromatic substitution in one‐pot. Mesophase characterization has been carried out by employing POM, DSC, and X‐ray diffraction studies. Photophysical properties were investigated using UV‐vis and emission spectroscopy. Furthermore, the charge transport properties were analyzed by time‐of‐flight measurements, and the observed ambipolar mobilities were found to be of the order of 10−3 cm2 V−1 s−1. The high solubility, excellent thermal stability, self‐organizing properties, and ambipolar charge transport characteristics make them promising candidates for applications in organic electronics. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs), whose refractive index can be changed by light irradiation, can be used as photoresponsive optical materials. In this study, an LC viologen was proposed as a novel photoresponsive compound that induced a change in the alignment of LC molecules (mesogens). An extended viologen with an asymmetric core, that exhibits a low-order LC phase at room temperature, was mixed with the well-known nematic LC compound (5CB) to prepare homogeneously aligned films. The change in the alignment of the mesogens was successfully induced by triggering a one-electron reduction reaction of the viologen moieties by light irradiation. [ABSTRACT FROM AUTHOR]

A homologous series comprises of eight mesogenic hydrogen bonded liquid crystal (HBLC) referred as nBAO + 4BU BA are designed, synthesized and characterized. All eight mesogens in nBAO + 4BU BA series are subjected to spectral, thermal and optical characterization. Formation of hydrogen bond in the resultant compounds is evinced by FTIR study. All eight mesogens obtained in this series exhibits only nematic phase in their entire thermal spans which are coined as Nematogens. Essential characteristic studies carried out on these nematogens are Parachromatism as a function of temperature, phase transition temperatures,mesogenic thermal span and enthalpy involved during phase transition respectively. [ABSTRACT FROM AUTHOR]

While the halogen bond has been recognised and studied for over a hundred years, it is only in more recent times that chemists have begun to apply it and see its possibilities as another supramolecular interaction that can be deployed in the preparation of materials. This review takes one of those areas, liquid crystals, and considers examples of motifs that have been deployed successfully to generate new mesogens. In particular, rather than attempting to be comprehensive, the article reviews critically data from well‐characterised systems and seeks to first make some comparisons with analogous hydrogen‐bonded materials, before considering how the lability and flexibility of the halogen bond expresses itself in liquid crystal behaviour. [ABSTRACT FROM AUTHOR]

The effect of core fluorination on the mesomorphic properties of rod-like Schiff base-derived liquid crystalline materials was reported. For this purpose, two new series of laterally fluorinated Schiff base liquid crystals are synthesised and investigated in detail. The two series differ from each other's in the length of the terminal alkoxy chain attached to one end of the aromatic core, where in the first series an octyloxy chain is used and in the second series it is replaced by a longer dodecyloxy chain. At the other end in both series of compounds, in addition to the nonsubstituted end (X = H) four different substituents were used (X = CH3O, C6H13O, CH3 and F). The molecular structures of all synthesised compounds were confirmed using different spectroscopic techniques. The molecular self-assembly was investigated using differential scanning calorimetry (DSC) and polarised optical microscope (POM). Depending on the length of terminal alkoxy chain at one end and nature of the substituent X at the other end, different types of mesophases were observed, including nematic and two different types of smectic phases. [ABSTRACT FROM AUTHOR]

Four series of di-flouro, namely; 4-substituted phenylazo-3-flouro phenyl-4'-n-alkoxy 3-flouro phenylazo benzoates (Ina-d) based on aromatic rings with the azo/ester/azo linkages core, were prepared and investigated for their mesomorphic properties. An alkoxy group with chain length varied from n = 6 to 16 is attached to the terminal phenylazobenzoate moiety and the other terminal is a compact group (X = --CH3O, --CH3, H and Br) attached to phenylazo moiety. The mesophases were investigated by DSC and POM and compared with previously investigated dilaterally methyl substituted analogues. Terminally unsubstituted and Br substituted analogues displayed dimorphic N and SmA phases, except the lower homologue (n = 6), while terminally -- CH3O analogues exhibited monomorphic N phase. For terminally -- CH3 substituted, compounds with n = 6-12 exhibited only N phase, while compounds with n = 14 and 16 displayed N and SmA phases. Meanwhile, the dilateral F substituents result in an enhancement in clearing thermal transitions compared with dilateral methyl substituents with a wide mesophase range. TGA analysis revealed that the prepared compounds are thermally stable within mesophase temperature range, except -- CH3O, --CH3 and Br derivatives with n = 6. Binary mixtures of I6a-d/I16a-d derivatives were investigated. The photo-physical property was also studied. [ABSTRACT FROM AUTHOR]

Many studies on the basis of cholesteric liquid crystal (CLC) have focused on dynamic optical changes utilizing photochemical reactions raising helical pitch variations. However, the conventional dyes doped in CLC system often show reversible isomerization such as trans‐cis, E‐Z, and open‐close forms that hampers the fixation of desired color cues. Here, a cyanostilbene‐based reactive mesogen (CSRM) for phototunable and subsequently polymerizable smart CLC paints is newly designed and synthesized. The structural color of the CLC paint can be precisely manipulated in remote controllable manner by inducing a photochemical reaction of CSRM. Due to the irreversible isomerization behaviors of CSRM, the constructed periodic structures with different helical pitches are intactly fixed via in situ photopolymerization under 460 nm light. In addition, the combination of helical nanostructures and cyanostilbene luminophore produces a circularly polarized light emission. The dissymmetry factor of circularly polarized luminescence is dependent on the photoregulated helical nanostructures in CLC films. The decoupled system of triple photofunctionality in a single component of chirophotonic crystalline material is applied to develop advanced optical information storages. [ABSTRACT FROM AUTHOR]

A new, 19 π‐delocalized electrons planar Blatter radical building block was developed and used to obtain paramagnetic bent‐core liquid crystals. The mesogens were investigated by optical, thermal, powder XRD and DFT methods in the pure form and as binary mixtures. Comparison of their properties with those of the classical Blatter radical analogues revealed that planarization of the central angular element results in a significantly higher stability of the mesophases and increased molecular organization suitable for the formation of ordered banana and columnar mesophases with tighter π–π interactions. These results indicate access to a new, potentially rich class of functional paramagnetic soft materials. [ABSTRACT FROM AUTHOR]

Secondary metabolites are considered one of the inspirations for designing new materials. Steroids form a diverse category of secondary metabolites, the derivatives of which constitute a prominent class of soft materials exhibiting various self-assembled structures. This report attempts to illustrate the importance of the oligo-ethyleneoxy side chain on the liquid crystallinity of steroidal mesogens. The ethyleneoxy benzoates of sterols were found to show cholesteric and polymorphic smectic mesophases along with frustrated phases such as TGB and blue phase. The mesogenic tendency of these molecules was analyzed as a function of the length of the ethyleneoxy side chain as well as the steroidal moiety. Furthermore, these derivatives have been investigated for their amphotropic behavior. The analysis was carried out using POM, DSC, SAXS, and SEM techniques. [ABSTRACT FROM AUTHOR]

Flexoelectric polarization, which is caused by symmetry breaking in a distortion of material, was investigated in liquid crystalline elastomers composed of wedge-shaped mesogens prepared by cross-linking under horseshoe-shaped deformation. X-ray diffractometry suggested that splay distortion along the depth direction was induced in the pseudo-isotropic phase. While almost no electric charge was observed in the smectic A phase, an electric charge caused by polarization due to the flexoelectric effect appeared and reached −1367 pC/mm2 in the pseudo-isotropic phase. We tentatively conclude that the macroscopic polarization due to the flexoelectric effect emerged and was fixed in the liquid crystalline elastomers by cross-linking under horseshoe-shaped deformation. [ABSTRACT FROM AUTHOR]

The synthesis and thermotropic behaviour of some di-alkyloxy-phenyl-1,2,4-triazolium trifluoromethane-sulfonate salts bearing a seven-carbon atom perfluoroalkyl chain on the cation is herein described. The fluorinated salts presenting a 1,2,4-triazole as a core and differing in the length of two alkyloxy chains on the phenyl ring demonstrated a typical liquid crystalline behaviour. The mesomorphic properties of this set of salts were studied by differential scanning calorimetry and polarized optical microscopy. The thermotropic properties are discussed on the grounds of the tuneable structures of the salts. The results showed the existence of a monotropic, columnar, liquid crystalline phase for the salts tested. An increase in the temperature mesophase range and the presence of two enantiotropic mesophases for the sixteen-atom alkyloxy chain salt can be observed by increasing the length of the alkyloxy chain on the phenyl ring. [ABSTRACT FROM AUTHOR]

The correlation between the size of nanoparticles, the structure and shape of mesogenic ligands and the ensuing assembly behaviour is not really understood. Closer inspection shows very surprising features. Here, 2‐ and 4‐nm gold nanoparticles (NPs) were synthesized, and grafted with a forked ligand containing two rod‐like mesogens in its branches: one cholesterol, the other with azobenzene. The 4‐nm NPs also contained n‐hexylthiol as co‐ligand. They were found to form a FCC cubic superlattice, whereas the 2‐nm NPs form hexagonal HCP with weak birefringence, hence with partially oriented ligands. The structures were compared with those of related systems containing a range of different azobenzene‐to‐cholesterol ratios, all giving body‐centred tetragonal superlattices with various degrees of anisotropy. Geometric analysis is presented in terms of the asphericity of the NPs' surroundings, requirement for space‐filling and structural anisotropy. Some general rules are derived to help design the soft corona around the NPs in order to obtain superlattices with the desired structure and anisotropy. [ABSTRACT FROM AUTHOR]

We are considering the propagation of circularly polarized light normally impinging on a cholesteric elastomer slab doped with metallic spheres. The slab is composed of two layers: the first layer is a right-handed chiral structure, and the second one is a helix with left-handedness; however, the pitch of the chiral structure remains constant. We performed a theoretical model to find numerically, reflection and transmission spectra for circularly polarized light impinging on the slab. We considered the effects of mechanical strains along the helical axis since the force exerted on the structure can tilt the mesogens in the slab along the helical axis. The Photonic Band-Gap(PBG) of the elastomer slab becomes narrowed because of the strain; there we also observe high reflectance (hyper-reflectivity) that depends on the filling factor of the silver doping and on whether the defect is located at a position that contains complete periods of the structure. Additionally, the spectra display reflection bands for both right- and left-polarized light. We expressed the PBG edges in terms of material parameters; this allows us to select the region of the electromagnetic spectrum for the reflection bands. This medium exhibits a hyper-reflective photonic band when the pitches of both right- and left-handed helical layers are identical. [ABSTRACT FROM AUTHOR]

Magnetorheological fluids (MRFs) are promising smart materials that can respond to an external field. In order to obtain stable suspension and investigate the settlement law of these synthesised MRFs, polymerised ionic liquid crystalline (PILC) ferroferric oxide nanocomposites (Fe3O4@PILCs), the dispersed phase in MRFs, were obtained by self-assembly of magnetic Fe3O4 nanoparticles with PILCs. The structural properties, thermotropic liquid crystal characteristics, morphology and microscopic magnetic response characteristics were investigated in this study. Fe3O4@PILCs showed nematic liquid crystal behaviour, and the mesogenic phase range was affected by the content of cholesteryl-based LC mesogen containing carboxylic acid groups. Series of MRFs were prepared by the Fe3O4@PILCs with 5% particles mass fractions in different volume fractions. The settlement stability as well as the settlement laws was investigated comprehensively and systematically for these MRFs. The Fe3O4@PILC-based MRFs exhibited better sedimentation stability than the bare Fe3O4-based MRFs, indicating that the Fe3O4 particles self-assembled with PILCs could reduce the density of the dispersed phase and showed the good compatibility with silicone oil carrier fluid. The sedimentation velocity curves of the Fe3O4@PILC-based with different particle volume fractions were investigated by use of some relevant theoretical models, indicating that they were the most consistent with the Dick's model. [ABSTRACT FROM AUTHOR]

Liquid crystalline elastomers (LCEs) represent a promising class of responsive polymers whose physical properties are peculiar to both fluids and solids. Thanks to their microscale structure made of elongated rigid molecules (mesogens)-- characterized by their capability to reversibly switch from an isotropic to an ordered state--LCEs exhibit a number of remarkable physical effects, such as self-deformation and mechanical actuation triggered by external stimuli. Efficient and physics-based modelling, aimed at designing and optimizing LCEbased devices (such as artificial muscles, deployable structures, soft actuators, etc.), is a fundamental tool to quantitatively describe their mechanical behaviour in real applications. In the present study, we illustrate the multi-physics modelling of lightdriven deformation of LCEs, based on the photothermal energy conversion. The role played by the light diffusion and heat transfer within the medium is considered and their effect on the obtainable actuation is studied through numerical simulations based on the multi-physics theory developed. [ABSTRACT FROM AUTHOR]

We review computer simulation studies of aided and self-assembly of nanoparticles that are decorated with liquid crystalline (mesogenic) ligands, termed hereafter as liquid crystalline nanoparticles (LCNPs). In bulk, LCNPs self-assemble into ordered morphologies, typically displaying a polydomain structure. We demonstrate that a range of monodomain morphologies can be grown by changing the density of ligands and employing external fields of specific symmetry, which act on mesogens. It is also demonstrated that the speed of self-assembly of LCNPs with chromophoric (e.g. azobenzene) mesogens can be increased by applying illumination at a certain wavelength and polarisation. Another case study covers the formation of an interconnected macromolecular network in a solution of the LCNPs in a polar solvent. Here, the network structure depends strongly on the decoration pattern of the LCNPs. Finally, the adsorption of LCNPs on a compatible liquid crystalline brush is discussed with a focus on the prerequisites and optimal conditions for this phenomenon. The review demonstrates the ability of classical particle-based models to produce a molecular-based understanding of the structure and interactions of LCNPs, and also to reproduce a wide set of physicochemical phenomena related to LCNP aided- and self-assembly processes. [ABSTRACT FROM AUTHOR]

Ferroelectricity is a desirable property of liquid crystalline materials. To enhance the ferroelectric properties, we optimised the molecular structure of the previously synthesised compounds DLm/n and prepared a series of (S)-lactate mesogens denoted ZL, which differ in a linkage of the non-chiral chain by an additional ether group. By this modification, we have succeeded in broadening the temperature range of a ferroelectric SmC* phase and spreading it down to room temperature, as well as in decreasing the melting points in comparison with the previously studied compounds. Also, the spontaneous electric polarisation of ZL compounds was found to be higher than that of parent mesogens. [ABSTRACT FROM AUTHOR]

The synthesis of bent-shaped mesogens and mesogenic dimers has renewed the field of liquid crystals in many ways during the previous decades, for example, through the discovery of 'exotic' mesophases such as the twist-bend nematic phase and the biaxial SmA phase (SmAb). Recently, we reported on the observation of a SmAb with a bent-shaped dimer, and on its fast electro-optic effect that we interpreted as a biaxial Fréedericksz transition (BFrTr) of the secondary m-director under applied electric field (C. Meyer et al., Phys. Rev. X, 11, 031012 (2021)). In this study, we used dielectric and birefringence techniques to directly measure the splay, K 11 m , and bend, K 33 m , elastic constants that characterise the elastic distortion modes of the m-director. We observed that during the BFrTr, domains of opposite tilt appear and are often enclosed in elliptical defect loops, just like those observed during the usual Fréedericksz transition of common nematics, which allowed us to obtain the third (twist) elastic constant K 22 m , from the defect loop ellipticity. Although K 11 m and K 33 m are of the same order of magnitude as K 11 and K 33 in the nematic phase of bent-shaped dimers, K 22 m is an order of magnitude smaller than K 11 m and K 33 m and also than K 22 of 5CB. We argue that these features could be generic for the intercalated SmAb phase of bent-shaped dimers. [ABSTRACT FROM AUTHOR]