SmA Phase Research Articles

Interdigitated orthogonal smectic and cybotactic nematic mesomorphism in three-ring hockey-stick-shaped 1,2,4-oxadiazole mesogens

Although hockey-stick-shaped liquid crystals with three-ring molecular architecture show remarkable thermal behavior, work on such systems is rarely reported. In particular, the investigations incorporating the novel oxadiazole core, which provides thermal and hydrolytic stability as well as polarity, have been scarcely presented. Given these observations, we intended to investigate such LCs derived from 3,5-diphenyl-1,2,4-oxadiazole. In this study, we report on the synthesis and elaborative characterization of a novel series of hockey-stick-shaped mesogens namely, methyl 4-(5-(4-n-alkoxyphenyl)-1,2,4-oxadiazol-3-yl)benzoate. To reveal the structure-property correlations, the substitution on the C-3 core in the form of methyl ester group has been held constant, while the substituent on the C-5 core has been varied with different n-alkoxy tails. While the thermal gravimetric analysis confirms the thermal stability, the methodical studies on the mesomorphism using optical, calorimetric, and X-ray diffraction techniques confirmed the occurrence of smectic A and nematic phases having interdigitated and cybotactic orders respectively. The lower and middle/higher members, respectively, show the N phase, and N and SmA phases, which follow the general trend reported hitherto for the homologues series of LC compounds. The quantum mechanical calculations using density functional theory revealed the bending angles, dipole moments, and HUMO/LUMO band gaps.

Phase Behaviors and Photoresponsive Thin Films of Syndiotactic Side-Chain Liquid Crystalline Polymers with High Densely Substituted Azobenzene Mesogens.

Azobenzene-containing polymers (azopolymers) are a kind of fascinating stimuli-responsive materials with broad and versatile applications. In this work, a series of syndiotactic C1 type azopolymers of Pm-Azo-Cn with side-chain azobenzene mesogens of varied length alkoxy tails (n=1, 4, 8, 10) and different length alkyl spacers (m=6, 10) have been prepared via Rh-catalyzed carbene polymerization. The thermal properties and ordered assembly structures of thus synthesized side chain liquid crystalline polymers (SCLCPs) have been systematically investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM) and variable-temperature small/wide-angle X-ray scattering (SAXS/WAXS) analyses. P10-Azo-C1 and P10-Azo-C4 with shorter alkoxy tails exhibited hierarchical structures SmB/Colob and transformed into SmA/Colob at a higher temperature, while P10-Azo-C8 and P10-Azo-C10 with longer alkoxy tails only displayed side group dominated layered SmB phase and transformed into SmA phase at higher temperatures. For P6-Azo-C4 with a shorter spacer only showed a less ordered SmA phase owing to interference by partly coupling between the side chain azobenzene mesogens and the helical backbone. More importantly, the series high densely substituted syndiotactic C1 azopolymer thin films, exhibited evidently and smoothly reversible photoresponsive properties, which demonstrated promising photoresponsive device applications.

New Series of Hydrogen-Bonded Liquid Crystal with High Birefringence and Conductivity.

Liquid crystals with high dielectric anisotropy, low operational thresholds, and significant birefringence (Δn) represent a key focus in soft matter research. This work introduces a novel series of hydrogen-bonded liquid crystals (HBLCs) derived from 4-n-alkoxybenzoic, 4-alkoxy-3-fluorobenzoic derivatives (nOBAF), 4-alkoxy-2,3-fluorobenzoic derivatives (nOBAFF), and 2-fluoro-4-nitrobenzoic acid. The HBLCs were characterized using Fourier transform infrared spectroscopy, and their thermal behavior was evaluated via differential scanning calorimetry. Optical observations were conducted using polarized optical microscopy. The results indicate that mixtures containing benzoic acid with a bilateral fluorine substituent exhibit both SmA and SmC phases, while those with a unilateral fluorine substituent exhibit nematic and SmA phases. Moreover, an increase in the length of the alkoxy chain results in an expanded mesophase temperature range. This study demonstrates that the presence of a fluorine substituent and the incorporation of an NO2 group in the molecular structure result in an increase in dielectric permittivity, DC conductivity, dielectric anisotropy, and birefringence.

Density functional theory of freezing transition in a binary mixture of spheres and soft-ellipsoids

ABSTRACT This study uses the classical density functional theory (DFT) of freezing to investigate phase transitions in ellipsoidal-spherical binary mixtures interacting via a generalised Gay-Berne (GB) intermolecular potential, with a focus on I-N, I-SmA and N-SmA transitions. The mixtures, consisting mainly of ellipsoids, contain spherical additives at concentrations of 5 % , 10 % and 15 % . The pair correlation functions, which are crucial for the DFT, are derived from Percus-Yevick integral equation theory. Our results show a significant influence of spherical additives on liquid crystalline phases formed by ellipsoids. At an ellipsoid length-to-width ratio of 3.0, only the I-N transition is observed, with the SmA phase remaining unstable under all conditions. Increasing the ellipsoidal length-to-width ratio to κ = 4.0 introduces the SmA phase, whose stability depends on the concentration and size of the spherical additives. The stability of the SmA phase decreases with increasing concentration and size of the spheres. Phase diagrams, which are shown in temperature-density and pressure-temperature planes, emphasise the influence of the size of the spherical dopants on the phase stability.

Terminal halogen-containing rod-like liquid crystals: Synthesis, self-assembly, photophysical and mechanochromism properties

Five series of cyanostilbene-based rod-like liquid crystals containing one different terminal atom (H, F, Cl, Br and I) at one end and one terminal aliphatic chain with different numbers of carbon atoms at the other end were reported by Suzuki coupling and Knoevenagel reactions. The influence of terminal halogen atoms and terminal chain length on the self-assembly, AIE behavior, temperature-dependent emission and mechanochromism behavior was explored by POM, DSC, XRD, SEM, absorption spectra and emission spectra. All the compounds are enantiotropic liquid crystals. The lowest non-halogen substituted homologue exhibited solo N phase, but the higher non-halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature. All the lowest halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature and all the higher homologues only exhibited SmA. The distinct mesogenic phase transition could be attributed to the intermolecular interaction produced by terminal halogen and the rigidity of the terminal aliphatic chain. All the non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom) exhibited AIE behaviors, whereas the iodinated compounds exhibited extremely weak emission in solution and aggregated states due to the heavy atoms effect. These compounds also exhibited distinct solid-state emission with blue or cyan fluorescence, which could be quenched by increasing temperature. The reversible mechanochromism behavior was also achieved in all the compounds. The mechanical force induced quench in emission in non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom), whereas enhancement in iodinated compounds. The reversible mechanochromism behavior endowed these compounds with potential applications in rewritable paper and anti-counterfeiting. The interesting properties in these liquid crystals would be attributed to the balance of the halogen-halogen interactions, heavy atom effect, steric-hindrance effect and chain length. These investigations would be helpful to understand the relationship between chemical structures and properties.

Probing the mesophase formation in thermotropic liquid crystal HBDBA using temperature-dependent Raman spectroscopy and DFT method

Liquid crystalline properties of the synthesized liquid crystal (LC) N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene) azines (HBDBA) are probed thoroughly using the comprehensive array of techniques e.g. differential scanning calorimetry (DSC), differential thermal analysis (DTA), polarizing optical microscopy (POM), temperature-dependent Raman spectroscopy and density functional theory (DFT) method. In this study, intricate molecular interactions crucial for mesophase formation of liquid crystalline system HBDBA and molecular rearrangement that occurs during LC transitions are unravelled comprehensively. Remarkably, at the Cr → SmA phase transition, the peak position, linewidth, and intensity of signature Raman bands are prominently changed. A thorough analysis of Raman marker bands and DFT calculation confirm the disruption of intramolecular hydrogen bonds in HBDBA at the Cr → SmA transition. The conclusion of the present study enriches the understanding of the underlying mechanisms of mesophase formation and intricate molecular interactions and arrangement at the molecular level of the thermotropic LC.

Linear and Nonlinear Electro-optic Response of MHPOCBC

This study investigated the linear and second-order electro-optic responses in chiral smectic liquid crystal 4-(1-methylheptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). The result revealed a single Debye-type relaxation in the linear electro-optic frequency dispersion, with a relaxation frequency extending up to one hundred kHz. Conversely, the second-order electro-optic response exhibited intricate temperature-dependence, accurately depicted by a phenomenological Landau theory around the SmA–SmCa* phase transition point. Notably, in the SmCa* phase, critical slowing down of the amplitude mode occurred near the transition to the SmA phase, while at lower temperatures of the SmCa* phase, a distinct low-frequency relaxation mode emerged. Furthermore, the relaxation frequency of the antiferroelectric Goldstone mode in the SmCA* phase remained constant across the entire temperature range. These findings should significantly contribute to the understanding of dynamic behaviors in chiral smectic liquid crystals, shedding light on their complex phase transitions and electro-optic properties.

A multiscale constitutive model of magnesium-shape memory alloy composite

In this work, a multiscale constitutive model is established to describe the deformation behaviors of magnesium-shape memory alloy (Mg-SMA) composite in a wide temperature range and reveal the strengthening mechanism of SMA reinforcement on Mg. The model is established at the grain scale firstly and gradually transited to the macroscopic scale by employing a newly developed three-level scale transition rule. At the grain scale, the thermodynamic-consistent constitutive models of Mg and SMA are, respectively, constructed by addressing different inelastic deformation mechanisms. The basal, prismatic, pyramidal, slip systems and extension twinning system are considered for the Mg phase, and the martensite transformation (MT) and austenitic plasticity are addressed for SMA reinforcement. Thermodynamic driving forces of each inelastic deformation mechanism are derived from the dissipative inequality and the constructed Gibbs free energies. At the polycrystalline scale, to evaluate the interactions among the grains and pores, and obtain the whole responses of the polycrystalline Mg and SMA, a thermo-mechanically coupled self-consistent homogenization scheme is employed. At the mesoscopic scale, a modified thermo-mechanically coupled Mori-Tanaka's homogenization scheme is adopted to evaluate the interaction between the Mg phase and SMA phase, and predict the whole responses for the representative volume element (RVE) of the composite. According to the geometrical features and mechanical loadings applied on the specimen, a hypothesis of homogeneous stress and strain fields at the macroscopic scale is adopted to achieve the scale transition from the RVE of the composite to the whole specimen. The capacity of the multiscale model is verified by comparing the predictions with the existing experimental data (Aydogmus, 2015). Moreover, the influences of characteristic information for the microstructures at different spatial scales on the deformation behaviors of the composite are predicted and discussed.

Dynamic change of molecular conformation generating a variation of liquid crystalline phases for triphenylene mesogens with peripheral alkoxyazobenzenes

ABSTRACT A triphenylene mesogen which possesses six dodecyloxyazobenzene units at the periphery linked by propylene-ether chain (2-C12-3) was synthesised and its mesomorphic phase transition behaviour was investigated. It was found that 2-C12-3 exhibits six mesophases including one monotropic phase. The calamitic-discotic bi-mesomorphic phase transition was also observed. As cooling the compound at the temperature of iso phase, SmA phase comes up and further cooling gives Col ob phase. In comparison to the corresponding ester-linked derivative (1-C12-3), which shows only two mesophases (SmA and Colr), the linkage part connecting triphenylene unit and the peripheral alkoxyazobenzenes significantly affect the molecular ordering in mesophase, though the bi-mesomorphic property is maintained in the case of dedecyloxy chains.

Implementation of Expectation Value and Variance in Decision-Making with Risk in Economic Learning in High School

Learning outcomes in economics learning at SMA Phase E that are related to material on production activities are that students understand the economic system as a way of organizing various economic activities to meet the various needs of society. Decision-making is commonly found in production activities, and every decision-making process has risks. To overcome this, the concept of probability is needed. Decision-making needs to be taught to students so that they can understand economic activities, which are always dynamic in nature, and the impact of these economic dynamics. Therefore, in learning economics, especially in material on production activities related to decision-making with risk, teachers can start with the theory of expected value and variance so that production activities do not experience losses and can even increase profits. This research aims to explore the relationship between statistical material and economics learning in high school. The research method used is a literature study method and is descriptive-qualitative in nature. The results show that economics teachers in high schools can teach and implement opportunity theory in economics learning in Phase E high schools to equip students to manage various economic activities, especially production activities.

Terminal methylene biphenyl derived coumarin Schiff base-esters: Synthesis, mesomorphic behaviour and DFT investigations

In the present investigation new unsymmetrical coumarin-methylene biphenyl MBPCE-(2–16) mesogens were designed and synthesized. Methylene biphenyl end group at one end of molecules have been linked to the 7-alkyloxy substituted coumarin core through imine and ester mesogenic connecting units. The structures of new hybrids have been elucidated employing different analytical techniques including FT-IR, 1H NMR, 13C NMR, Mass & CHN elemental analysis. New molecules have been investigated for their mesomorphic behaviour using DSC (Measurement of transition temperature and enthalpy associated) and POM (Texture study) techniques and the existence of mesophase was established by VT-XRD analysis. Compounds with n = 2 (-OC2H5) to n = 7 (-OC7H15) chain length exhibited enantiotropic nematic mesophase with good thermal stability. As the chain length increases, compounds from n = 8 (-OC8H17) and n = 10 (-OC10H21) displayed enantiotropic nematic as well as smectic-A mesophase whereas compound with n = 12 (-OC12H25) showed only interdigitated SmA phase. Next two members of the series failed to show any mesomorphism. The commencement of SmA phase and disappearance of nematic could be attributed to more layer arrangement with increased van der waals interactions. The density functional theory (DFT) calculations were employed to complement the experimental results concerning the mesomorphic behaviour. Development of smectic phase could be due to the augmentation in the area of the intermolecular interaction which increases the degree of molecular packing. Conversely, it was discovered that higher polarizability leads to lower nematic thermal stability because it strengthens parallel intermolecular interactions, which promotes a higher degree of molecular order while reducing the development of lower-order nematic mesophase.

Novel liquid crystalline fluorene and fluorenone MIDA boronates: influence of alkyl vs alkoxy side chains on the mesomorphic properties

ABSTRACT To obtain novel boron liquid crystals, we successfully combined MIDA boronates with chromophoric fluorene and fluorenone mesogenic units and studied the influence of alkoxy versus alkyl side chains by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). The fluorenes showed broader temperature ranges of the SmA phase compared to their fluorenone counterparts. By replacing the alkoxy side chains with alkyl side chains, the mesophase ranges could be significantly enlarged and the thermal stability increased.

Glassy relaxation in a de Vries smectic liquid crystal consisting of bent-core molecules.

We report experimental investigations of a liquid crystal comprising thiophene-based achiral bent-core banana shaped molecules. The compound exhibits the following phase sequence on cooling: Isotropic (517.4K), N (514.9K), de Vries SmA (402K), SmC. Practically no layer contraction was observed across the SmA to SmC transition, confirming the "de Vries" nature of the SmA phase. Interestingly, the crystallization does not occur on cooling the sample, unlike most other liquid crystals. Instead, the SmC phase undergoes a glass transition at 271K even at a slow cooling rate. The dielectric spectroscopy studies carried out on the sample reveal the presence of a dielectric mode whose relaxation process is of the Cole-Cole type. The relaxation frequency of the mode was found to drop rapidly with decreasing temperature, confirming the glassy behavior. The variation of relaxation frequency with temperature follows the Vogel-Fulcher-Tammann equation, indicating the fragile glassy nature of the sample. This report identifies a bent-core liquid crystal exhibiting a "de Vries" SmA phase and glassy behavior at lower temperatures.

The interplay of chirality and restricted rotation: stabilisation of chiral, frustrated mesophases over a wide thermal range.

Introducing restricted rotation in a molecule, often achieved through the incorporation of double or triple bonds, constitutes a crucial approach to induce a frustrated mesophase. Furthermore, the inclusion of a chiral moiety, such as cholesterol, serves to enhance the stabilization of chiral frustrated mesophases. This study presents the synthesis and characterization of novel optically active dimers incorporating cholesterol and phenyl 3-phenylpropiolate segments interconnected by an ω-oxyalkanoyloxy spacer with varying lengths and parity. Comprehensive characterization using POM, DSC, and X-ray diffraction techniques reveals that these mesogens exhibit enantiotropic liquid crystal (LC) phases. Due to the restricted rotation caused by the triple bonded system, these dimers stabilized the frustrated chiral mesophase TGBC* over a wide temperature range. The identified phases include BP-I/II, N*, and SmA, with odd-membered dimers commonly displaying N* and SmA phases and one member additionally exhibiting BP-I/II. Even-membered dimers exhibit N* and TGBC* phases, with the latter spanning an impressive thermal range of 37 °C to 84 °C. Notably, the thermal range of the TGBC* phase widens with an increase in the terminal tail length. Across the series, clearing temperatures generally decrease with the elongation of the terminal tail, and even-membered dimers consistently exhibit higher clearing temperatures than their odd-membered counterparts, illustrating the spacer's parity-dependent odd-even effect on the dimers' phase transition behavior.

Lithium salt of a pro-mesogenic [closo-CB11H12]- derivative: anisotropic Li+ ion transport in liquid crystalline electrolytes.

Li+ ion conduction in two aligned liquid crystalline electrolytes consisting of 10 mol% Li+ salt of a pro-mesogenic anion derived from [closo-1-CB11H12]- in non-ionic hosts was investigated. Using electrochemical impedance spectroscopy (EIS), the ionic conductivity in the parallel (σ‖) and perpendicular (σ⊥) directions of the electrolyte samples was determined using two types of cells: an interdigitated gold electrode and a nylon 6-coated ITO cell. The ratio of ionic conductivities σ⊥/σ‖ in the electrolyte with a nona(ethylene oxide) spacer was about 3 in the entire SmA phase, while in the shorter homologue, the ratio monotonically increases from about 0.4 to 2.9. The liquid crystalline behavior of the hosts and the electrolytes was investigated by optical, thermal, and powder XRD methods.

Optical and calorimetric studies near the smectic-A to smectic-C tricritical point

Detailed heat capacity and birefringence measurements have been performed to investigate the transitional behavior near the orthogonal smectic-A to tilted smectic-C (Sm-A–Sm-C) phase transition on several liquid crystalline mixtures comprising of a rod-like mesogen and a hockey stick-shaped compound having substitution of methyl group in the lateral position. Both probing methods were found to be rather successful in assessing the phase transitional behavior with reasonably good accuracy. The data shows a divergent pretransitional excess above and below the transition temperature. Analysis of the data have been performed in detail with the renormalization-group expression with correction-to-scaling terms. The extracted effective critical exponents were observed in between the tricritical and 3D-XY limit. Detailed investigations carried out in this work reveal the dependence of the Sm-A–Sm-C phase transition on the width of the Sm-A phase and the existence of a broad tricritical range.

Influence of the molecular structure of compounds differing with terminal polar group on the induction of the smectic A phase. Part III

ABSTRACT The aim of this work is to determine the influence of the terminal polar group of nematic compounds, namely -OCF3, -NCS, -CN, -F, on the induction of the SmA phase in their mixtures with compounds having terminal non-polar groups. The former group of compounds has positive dielectric anisotropy, and the latter negative. The phase transition temperatures of binary mixtures were measured using polarising thermomicroscopy, and phase diagrams for investigated systems were constructed. The strength of the SmA phase induction increases upon the increase of the polarity of compounds. The strongest induction is observed in systems with compounds having a terminal trifluoromethoxy group. Although compounds with the cyano group have the highest polarity, their ability for the SmA phase induction is smaller due to their dimerisation.

Smectic behaviour of α,ω-alkanediol diesters of a partially fluorinated 4-dodecyloxybenzoic acid: the odd-even effect

ABSTRACT 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.

Synthesis and mesomorphic properties of bent liquid crystals containing triazole mesogenic unit with terminal flexible alkyl chain and laterally ethoxy substituted Schiff base

ABSTRACT A new series of bent-shaped liquid crystals containing a triazole ring were synthesised and characterised at ambient and elevated temperatures. The triazole-cored and bent liquid crystals possess a flexible alkyl chain at one terminal, while the other side of the core is connected by a laterally ethoxy Schiff base consisting of a CN-biphenyl moiety. The evaluation on optical and thermal properties was carried out by polarising optical microscope and differential scanning microscope which revealed the length of the alkyl chain, –CnH2n + 1, that influenced the mesophase and the related clearing temperatures (Tc). Whilst the compounds with higher number of n possess lower Tc points, the presence of SmA phase seemed to be more favourable for the compounds in which the alkyl chain length was n ≥ 12. This observation can be associated with its bending angle and charge distributions along the two arms of which the interaction between the opposite counterparts of both arms in these bent-liquid crystals would promote the formation of SmA phase. The computational calculations based on density functional theory were performed to further support the transition from non-mesomorphic to SmA phases upon the increase in alkyl chain length (n), dipole moment and polarity which contribute to its stability.

Electric field effects on N–Sm-A–Sm-C phase transitions

A liquid crystalline system formed by rod-shaped molecules that have a small transverse dipole moment is analyzed in the presence of an external electric field normal to the smectic layers. The approach focuses on the phase transition diagram displaying the N–Sm–A-Sm-C phases, when both negative and positive dielectric anisotropies are considered. The analysis is carried out within the framework of an extended mean field theory, which shows the emergence of a re-entrant Sm-C phase in the strong field regime, accompanied by a suppression of the translational ordering of the Sm-A phase, in the case of a negative anisotropy. A different scenario is observed in the case of positive anisotropy, as the electric field tends to suppress the Sm-C phase because the molecular alignment is driven by the field along its direction. In this case, the emergence of a residual nematic phase is also observed, which replaces the isotropic phase and is characterized by a low-value orientational order parameter.