Mesogenic Phase Research Articles

Non-conventional multi-arm ester liquid crystal derived from cholic acid: synthesis, thermal and optical behaviour

ABSTRACTWith cholic acid as the core, five multi-arm ester liquid crystals were synthesised with different terminal substituents. B1–B5 were mesogenic arms which were linked to multifunctional chiral core cholic acid. The effect of electron-withdrawing and electron-donating groups on the mesogenic behaviour of the compounds was discussed. All products were structurally well characterised by elemental analysis, 1HNMR, and FT-IR. The phase behaviours were investigated by means of polarised optical microscopy and differential scanning calorimetry. B2, B4, B5 and C2, C4, C5 and D2, D4, D5 exhibited typical nematic texture and belonged to thermotropic enantiotropic nematic liquid crystals. B3, C3 and D3 also displayed typical nematic texture of thermotropic monotropic nematic liquid crystal. B1, C1 and D1 did not have mesogenic performance. Wider mesogenic range for 81.6°C of C5 whose terminal substituent is nitro on heating cycle while 121.1°C on cooling cycle. The results indicated that terminal substituents have a pretty important effect on the mesogenic phase and range of multi-arm liquid crystal compounds. The mesomorphic behaviour of compounds with polar groups terminally substituted performance much better than those without polar groups. In this ester multi-arm liquid crystal system, electron-withdrawing groups terminally substituted behave better than those electron-donating groups substituted.

Investigation of the heliconical smectic SmCSPFhel phase in achiral bent-core mesogens derived from 4-cyanoresorcinol

Investigation of the heliconical smectic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>SmC</mml:mi><mml:mi>S</mml:mi></mml:msub><mml:msubsup><mml:mi mathvariant="normal">P</mml:mi><mml:mrow><mml:mi>F</mml:mi></mml:mrow><mml:mrow><mml:mi>h</mml:mi><mml:mi>e</mml:mi><mml:mi>l</mml:mi></mml:mrow></mml:msubsup></mml:mrow></mml:math> phase in achiral bent-core mesogens derived from 4-cyanoresorcinol

Deconstruction of microfibrillated cellulose into nanocrystalline cellulose rods and mesogenic phase formation in concentrated low-modulus sodium silicate solutions

This work demonstrates for the first time the deconstruction of microfibrillated cellulose (MFC) into rod-like cellulose nanocrystals (CNCs) in concentrated low modulus sodium silicate solutions. To this aim, MFC suspensions at different concentrations were first treated in sodium hydroxide solutions and then amorphous silica powder was added. Optical microscopy and transmission electron microscopy observation showed how MFC was efficiently deconstructed into CNCs, evidencing the occurrence of a phase separation into an isotropic and mesogenic phase. The extracted CNCs were characterized by a remarkably higher length (600–1200 nm) in comparison with the plant-derived ones commonly reported in literature. FT-IR spectroscopy and 29Si MAS NMR confirmed that the Qn equilibrium of the suspended silicate species was affected, proportionally to the amount of MFC. It was also shown, that due to the excluded volume effect exerted by silicate anions, nematic or smectic ordering could be achieved for CNC concentrations far below the critical rod concentration predicted by the Doi-Edwards model.

Electro-optical, thermal and dielectric properties of ternary mixture of E7/6CB/6BA liquid crystal mixture complex

In this study, a novel liquid crystal mixture complex was designed and synthesized from the nematic liquid crystal mixture E7, hexylcyanobiphenyl (6CB) and hexylbenzoic acid (6BA). The thermal and morphological properties were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The DSC and POM results show that the liquid crystal complexes exhibit liquid crystalline properties with smectic and nematic phase. While the E7 ratio is 80%, the mixture complex has the widest nematic range and exhibits E7 properties. When the E7 weight ratio is less than 80%, with the formation of hydrogen bonds the number of mesogenic phases increases and the nematic range decreases. The electrical properties of obtained samples were measured by impedance spectroscopy technique. The birefringence and contrast ratio of samples also investigated by the help of light transmittance experiment.

Mirror symmetry breaking in liquids and liquid crystals

ABSTRACTIn the recent two decades liquid crystal science has contributed significantly to the understanding of mirror symmetry breaking and spontaneous emergence of chirality in fluids. This account tries to summarise the current state of understanding of mirror symmetry breaking in the liquid and liquid crystalline mesophases, ranging from isotropic liquids, via cubic, columnar and tetragonal SmQ phases of polycatenar compounds, the twist bend nematic phases of bent dimesogens to the heliconical and conglomerate type smectic phases of bent-core mesogens. Especially, the importance of dynamic chirality synchronisation of molecular conformers, cooperativity, helical superstructures, layer chirality, network formation, as well as chiral and achiral surface effects is discussed. At the end the transition from local to absolute symmetry breaking, chirality amplification and the relevance for the emergence of uniform chirality in prebiotic fluids and biosystems are considered.

Experimental and computational (DFT) studies on induced orthogonal smectic A∗ phase in hydrogen-bonded ferroelectric liquid crystals

Hydrogen-bonded ferroelectric liquid crystals (HBFLC) are designed and synthesized from nonmesogenic chiral proton donor compound of (R)-([Formula: see text])-Methylsuccinic acid (MSA) and mesogenic proton acceptor compound of 4-undecyloxybenzoic acid (11OBA) in a different mole ratio. Intermolecular hydrogen bonds (H-bond) between the nonmesogenic and mesogenic compounds have been confirmed through experimental Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) computational studies. The steric hindrance and inductive effects of the present complex and its influence on the structure are discussed. A rich phase polymorphism in the liquid crystalline complex has been studied using polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The chiral phases observed in the present complex are due to the presence of lone pair (n) to anti-bonding ([Formula: see text]) transition symmetry which is validated by DFT studies. A noteworthy observation of induced smectic A[Formula: see text](Sm A[Formula: see text]) by quenching of traditional phase (nematic) has been identified and the reason for the same has been discussed by DFT studies. The unusual phase order of Sm A[Formula: see text], smectic C[Formula: see text](Sm C[Formula: see text]) and smectic G[Formula: see text][Formula: see text](Sm G[Formula: see text]) mesogenic phases are observed. The other liquid crystalline parameters are evaluated by experimental and theoretical calculations and the same has been compared. Increased tilt angle in liquid crystal (LC) molecules has been theoretically analyzed by natural bond orbital (NBO) studies. Stability of the HBFLC phases and its origination mechanism have been discussed with the help of highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) energies.

H–bonded mesogenic unsymmetric bis-heterocycles

Five new series of bis−heterocycles containing isoxazole and pyrazole were reported, and their mesomorphic properties were investigated. A polar phenolic−OH group incorporated in compounds 1b–c and 1e is to probe the possible H−bonds induced. Two single crystals of mesogenic compounds 1a and 1b (all n=8) were obtained, and their single crystal and molecular structure were resolved. Intra− and intermolecular H−bonds observed in both crystal lattices were probably attributed to the formation of mesophases in these bis−heterocyclic structures. The CH−π interaction was also found to be important. All the precursors 2a−d were mesogenic, giving N, SmA, or/and SmC phases, however, other compounds 2e were not mesogenic. On the other hand, bis−heterocyclic compounds 1a−c were mesogenic, exhibiting SmC or SmA phases, and other compounds 1d−e were not mesogenic. The shape effect and H−bonds induced inherently from the core might be attributed to the formation of the mesophases in these bis−heterocycles. All derivatives showed good stabilities at temperature below T=299−327°C on TGA. The PL spectra of all compounds 1a−e showed one intense peak at λmax=317−386 nm, and these photoluminescent emissions originated from heterocyclic core.

New isothiocyanato liquid crystals containing thieno[3,2-b]thiophene central core

ABSTRACTNew isothiocyanato liquid crystal (LC) materials based on thieno[3,2-b]thiophene core have been synthesised and characterised. Their mesomorphic and physical properties were evaluated. The results indicate that most of the new compounds exhibit only enantiotropic smectic A phases with high clearing points, and the difluorinated compounds (A3 and A6), in particular, also display a stable nematic phase with low melting points. Compared with the corresponding biphenyl and thiophene-phenyl analogues, these thieno[3,2-b]thiophene-based compounds possess increased birefringence (the highest value found to be 0.40) and mesogenic phase intervals. These new thieno[3,2-b]thiophene-based LCs exhibit a high birefringence and a high clearing point and are of potential use as components of high birefringence mixtures.

Induced Smectic X Phase Through Intermolecular Hydrogen-Bonded Liquid Crystals Formed Between Citric Acid and p-n-(Octyloxy)Benzoic Acid

Hydrogen-bonded liquid crystal (HBLC) is synthesized from citric acid (CA) and 4-(octyloxy)benzoic acid (8OBA) with different mole ratios. Fourier transform infrared spectroscopy (FT-IR) confirms the presence of hydrogen bond between CA and 8OBA. Nuclear magnetic resonance (NMR) spectroscopic studies validate the intermolecular complementary, cyclic type of hydrogen bond, and molecular environment in the designed HBLC complex. Powder X-ray diffraction analysis reveals the monoclinic nature of liquid crystal complex in solid phase. Liquid crystal parameters such as phase transition temperature and enthalpy values for the corresponding mesogenic phases are investigated using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). It is observed that the change in chain length and steric hindrance while increasing the mole ratio in HBLC complex induces a new smectic X (Sm X) along with higher-order smectic G (Sm G) phases by quenching of smectic C (Sm C). From the experimental observations, induced Sm X phase has been identified as a finger print texture. Also, Sm G is a multi-colored mosaic texture in 1:1, 1:2, and 1:3 mol ratios. The optical tilt angle, thermal stability factor, and enhanced thermal span width of CA + 8OBA complex are discussed.

Low-temperature nematic phase in asymmetrical 1,3,4-oxadiazole bent-core liquid crystals possessing lateral methoxy group

ABSTRACTAsymmetrical bent-core molecules based on 1,3,4-oxadiazole bent-core unit have been synthesised as a new design with a lateral methoxy group at outer phenyl ring of the molecule. These new asymmetrical bent-core molecules resemble hockey-stick shaped due to the presence of two different arms of different lengths. One arm of these molecules is elongated having two phenyl rings and possesses a 4-n-alkyloxy chain of a different number of carbon atoms (n = 4, 8, 12 and 18) and other arm is short and has one phenyl ring with fixed 4-n-octyloxy chain. The bent-core molecules possess a lateral polar methoxy group at the elongated arm of the molecule. These bent-core compounds exhibited fluorescence emission in the UV wavelength region (~377–386 nm) whereas in acetonitrile and dimethylformamide, solvent displays blue emission peak with a large stoke shift.The bent-core molecules with the number of carbon atoms (n = 4, 8 and 12) at the elongated arm exhibited monotropic nematic phase at low temperature, while the 4-n-octadecyloxy chain at the elongated arm displayed smectic A phase. Dielectric studies were performed in the nematic phase of the bent-core mesogens confirm the formation of the cybotactic cluster in the nematic mesophases.

Emergent Optical Phononic Modes upon Nanoscale Mesogenic Phase Transitions.

The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in inelastic X-ray scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems. The understanding of collective mode behavior with a Q-dependence is the key to implement heat management based on the control of a sample structure. The latter has great potential for a large number of energy-inspired innovations. As a first step toward this goal, we carried out high contrast IXS measurements on a liquid crystal sample, D7AOB, which exhibits solid-like dynamic features, such as the coexistence of longitudinal and transverse phononic modes. For the first time, we found that these terahertz phononic excitations persist in the crystal, smectic A, and isotropic phases. Furthermore, the intermediate smectic A phase is shown to support a van der Waals-mediated nonhydrodynamic mode with an optical-like phononic behavior. The tunability of the collective excitations at nanometer-terahertz scales via selection of the sample mesogenic phase represents a new opportunity to manipulate optomechanical properties of soft metamaterials.

Design, synthesis and characterization of hydrogen bonded thermotropic liquid crystals

ABSTRACTA homologous series of seven linear hydrogen bonded thermotropic liquid crystals are isolated from p-n-octyloxy benzoic acid (8BAO) and p-n alkyl benzoic acids (nBA, where n varies from 2 to 8). In all the seven complexes, hydrogen bonding is a result of complementary proton-donor and electron-acceptor pairs derived from carboxylic acids of 8BAO and nBA. Spectroscopic characterization such as Fourier Transform Infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (1HNMR, 13CNMR) are performed for all the seven complexes to confirm the intermolecular hydrogen bonding and the nature of chemical environment respectively. Seven mesogen are examined by Polarizing Optical Microscope (POM) for identification of the phase polymorphism through standard textures. Transition temperatures and corresponding enthalpy values of the individual mesogenic phases are experimentally obtained from the analysis of the respective Differential Scanning Calorimetry (DSC) thermograms. Phase diagram of this homologous series is constructed based on the data of transition temperatures, further qualitative analysis of the phase abundance is discussed. Thermal stability factor for each of the mesogenic phase has been determined. Order of phase transition is experimentally obtained by Navard and Cox technique. Specific heat for each phase transition of individual complexes is derived from the DSC data. Change of color of the texture with temperature in the same phase is referred as parachromatism and is observed in nematic phase of two mesogens.

Experimental investigation on the effect of mesogenic ratio in hydrogen-bonded liquid crystal complexes

ABSTRACTHydrogen-bonded liquid crystal complex (HBLC) is synthesized from mesogenic 4-hexyloxy benzoic acid (6OBA) and aliphatic non-mesogenic citric acid (CA). The presence of intermolecular hydrogen bond in the HBLC complex is confirmed by FTIR spectrum. Phase transition temperature and enthalpy values are identified using different techniques. Induced highly ordered smectic G phase has been noticed in the present HBLC complex. Thermal span width and thermal stability factor of the individual mesogenic phase are discussed. The complexes are synthesized in different mole ratios, and their corresponding influence on the phase transitions is also discussed.

1A14 キラルバナナ型液晶のB2相の強誘電・反強誘電性発現における偶奇効果(物理・物性)

1A14 キラルバナナ型液晶のB2相の強誘電・反強誘電性発現における偶奇効果(物理・物性)

The global liquid crystal phase diagram of the nematogenic square-well line model

ABSTRACTMonte–Carlo simulations in the isothermal–isobaric ensemble are employed to characterise the boundaries of isotropic, nematic, smectic and hexatic phases of square-well prolate spherocylinders with a continuous line of interaction sites. Our results show clear first-order phase transitions between the different mesogenic phases. This work considers different issues not previously published for this model that largely comprised the features of real substances without explicit energetical anisotropy parameters. Particular emphasis is given to the enhancement of the stability of the nematic phase in comparison with other prolate fluids of ellipsoidal and spherocylindrical geometry.

Investigation on Thermal and Optical Properties of Hydrogen-Bonded Binary Liquid Crystals

A homologous series of hydrogen-bonded liquid crystals (HBLCs) are synthesized and characterized. Intermolecular hydrogen bonding occurs between 4-methoxycinnamic acid (4MCA) and p-n-alkyloxy benzoic acids (nOBA, where n = 3, 7 to 12). These binary complexes have been obtained by following well-designed synthesis route. The subsequent binary complexes have been characterized by polarizing optical thermal microscopy (POM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The present work explains the details of the association between the mesogenic phase behavior and H-bonding in the homologous series of 4MCA + nOBA. Nematic phase is interrelated with the closed dimers between acid molecules through the formation of strong hydrogen bonds. But, high concentrations are linked to the manifestation of smectic phases that disturb the local order of the nematic phase. As a result, the higher-order mesophases are observed in the present binary complex series. The inclusion of nematic LC (4MCA) in the nOBA alters the melting temperature and the clearing temperature as lower than those of the individual. Also, the wide mesophase regions of the present series are identified compared to those of the constituent mesogens. The optical tilt angle of binary mixtures for smectic C phase and thermal stability factors of the mesogenic phases have been discussed.

Design and synthesis of hydrogen bonded binary mixture liquid crystals

ABSTRACTAn intermolecular hydrogen bond is formed between 4-undecyloxy benzoic acid (11BAO) and cholesteryl acetate (CHA) which has been confirmed by Fourier transform infrared (FTIR) spectroscopic studies. Phase transition temperatures and enthalpy values are experimentally evaluated by polarizing optical microscopic (POM) and differential scanning calorimetric (DSC) studies. An interesting feature in this paper is that the observation of wider thermal span of the mesogenic phases and decreased enthalpy values of all phases in the binary mixture compared to the individual mesogen. The resultant hydrogen bonded liquid crystal mixture complexes possess a Nematic phase with a high clearing point, and a low melting point compared to constituent in the complex.

Bulk organisation and alignment in Langmuir and Langmuir–Blodgett films of tetrachloroperylene tetracarboxylic acid esters

Perylene derivatives with chlorine atoms attached at the bay position to the dye core are expected to affect organisation and tendency to aggregation in Langmuir and Langmuir–Blodgett (LB) films. Therefore, newly synthesized core–twisted homologous series of tetrachloroperylene tetracarboxylic acid esters with n = 1,4,5,6,9 carbon atoms in terminal alkyl chains were studied. Phase transitions and crystalline structures were specified by differential scanning calorimetry (DSC) and single crystal X–ray diffraction (XRD), respectively. Intermolecular interactions and organisation of the dyes in monomolecular films were investigated by means of Brewster angle microscope (BAM), UV–Vis absorption and emission spectroscopy, fluorescence microscopy and atomic force microscopy (AFM).The dyes investigated do not form thermotropic mesogenic phases in bulk. The crystalline triclinic elementary cell with P–1 symmetry is revealed from X–ray experiments. In Langmuir and Langmuir–Blodgett films molecular tilted head–on alignment is postulated. Spectroscopic research confirmed by AFM texture images of the LB films show that in the Langmuir and LB films the dyes, depending on length of terminal chains, have a tendency to create H or I molecular aggregates. The impact of the twisted core on the molecular behavior in a bulk and thin films is discussed.

Search for microscopic and macroscopic biaxiality in the cybotactic nematic phase of new oxadiazole bent-core mesogens

The possibility of biaxial orientational order in nematic liquid crystals is a subject of intense current interest. We explore the tendencies toward local and global biaxial ordering in the recently synthesized trimethylated oxadiazole-based bent-core mesogens with a pronounced asymmetric (bow-type) shape of molecules. The combination of x-ray diffraction and optical studies suggests that the biaxial order is expressed differently at the short- and long-range scales. Locally, at the scale of a few molecules, x-ray-diffraction data demonstrate biaxial packing. However, above the mesoscopic scale, the global orientational order in all three compounds is uniaxial, as evidenced by uniform homeotropic alignment of the nematic phase which is optically tested over the entire temperature range and by the observations of topological defects induced by individual and aggregated colloidal spheres in the nematic bulk.

Analysis of hydrogen-bonded liquid crystals formed between nitro-substituted benzoic acid and p-n-alkyloxy benzoic acids

ABSTRACTA novel series of hydrogen-bonded liquid crystals (HBLC) comprising of eight mesogenic complexes are formed between 3-Nitrobenzoic acid (NBAO) and p-n-alkyloxy benzoic acids (nBAO). The formation of inter molecular hydrogen bonding is evinced through FTIR spectra. Mesogenic phases are confirmed through the textural observations made by Polarizing Optical Microscope (POM) and their transition temperatures are correlated with the data obtained from Differential Scanning Calorimetry (DSC) studies. Phase diagram is constructed from POM and DSC studies. Odd–even effect has been evinced in the transition temperature and enthalpy values corresponding to the smectic C phase transition. Optical tilt angle in smectic C phase is fitted to a power law which reveals that the temperature variation of the tilt angle measurement follows the Mean Field theory predicted value. Thermal stability factor for the individual phase is also elucidated. Dielectric dispersion curves are obtained for the complexes exhibiting nematic phase.