Isotropic Temperature Research Articles

Tunable optical, electro-optical and dielectric properties of eco-friendly graphene quantum dots-nematic liquid crystal composites

ABSTRACT The changes in physical properties obtained by dispersing hydrophilic carboxylated graphene quantum dots (GQDs, <10 nm), which are non-toxic, biocompatible, and eco-friendly, into a room-temperature nematic liquid crystal, 5CB (4-pentyl-4ˈ- biphenylcarbonitrile) are described. Nematic–isotropic transition temperatures, polarising microscopy, electro-optic, photoluminescence, and dielectric investigations are reported for two composites having concentrations of GQDs of 0.25 and 1.0 wt.% in 5CB and compared to pristine 5CB. At the lower concentration (0.25%) of GQDs there is an enhancement in the order parameter by 5.49%, the birefringence by 1.28%, and the activation energy for dielectric relaxation by 4.4% compared to pure 5CB. However, at the higher concentration (1%), aggregation of GQDs occurs. This is apparent in optical textures and resulted in the deterioration of optical and electrical properties compared to 5CB. The photoluminescence spectrum of both concentrations of GQDs are centred at the same wavelength; however, the 1% GQD-5CB mixture exhibits significant quenching and may be suitable for some optical devices. Overall, our results support that, in addition to promoting sustainable, heavy-metal-free, and environmentally safe technologies, a low concentration of GQDs in LCs produces composites that have superior electrical and optical properties; thus, making them suitable for a variety of photonics and display applications.

Dimeric cyanopyridine with methylenebis(oxy)-based linker: A tactic to luminescent molecules exhibiting room temperature liquid crystalline property

The first example of luminescent, room temperature liquid crystalline molecules with methylenebis(oxy)-based linker, namely, 2,2'-(methylenebis(oxy))bis(4,6-bis(4-(alkyloxy)phenyl)nicotinonitrile) has been reported in the present work. The designed molecules have been synthesized using dichloromethane (DCM) as the reagent to obtain the methylenebis(oxy)-based linkers. The structural characterizations of the synthesized molecules were carried out by using ATR-IR, 1H NMR, 13C NMR, MALDI-TOF, and elemental analysis. Photophysical property examination of the molecules in the solution state indicated the deep blue emissive nature of the molecules with a relative quantum yield of about 27–32%. Further, electrochemical studies were performed on the molecules by using cyclic voltammetry and determined their underlying HOMO and LUMO energy levels as well as the associated band gaps. In contrast, DFT analysis was performed on the representative compound bearing methoxy groups in place of flexible alkoxy chains to obtain optimized geometry and further studied the distribution of electron density in its HOMO and LUMO energy levels. Furthermore, the liquid crystalline property examination revealed that all the molecules exhibited a smectic C phase upon cooling from isotropic temperature. Finally, the present study paves the way for the synthesis of dendrimer-type liquid crystals with methylenebis(oxy)-based linkers.

Synthesis and mesomorphic properties of novel multi-arm side-chain liquid crystal polymers with different terminal substituents

ABSTRACT In this study, two novel aromatic ester multi-arm liquid crystal monomers M 1 and M 2 with different terminal substituents centred on 3,4,5-trihydroxybenzoic acid, and a rod-shaped chiral liquid crystal monomer N were designed and synthesised. The synthesised liquid crystal monomers M and N were grafted and copolymerised with polymethylhydrosiloxane (PMHS). The structural characterisation of the synthesised liquid crystal compounds was carried out by FT-IR and 1H-NMR. The mesomorphic properties of the synthesised liquid crystal compounds were characterised by POM and DSC, and the results showed that the multi-arm liquid crystal monomers M 1 and M 2 are typical enantiotropic nematic liquid crystal compounds and N is typical thermotropic enantiotropic cholesteric liquid crystal. Polymers P 1 and P 2 are both cholesteric liquid crystal polymers. The glass transition temperatures and liquid crystal isotropic transition temperatures of polymers P 1 and P 2 series both tend to increase with the increase of multi-arm liquid crystal monomer M.

Can even-membered liquid crystal dimers exhibit the twist-bend nematic phase? The preparation and properties of disulphide and thioether linked dimers

ABSTRACTCyanobiphenyl-based liquid crystal dimers containing a disulfide link in the spacer, the 4-[4-[2-[2-[4-(4-cyanophenyl)phenyl]alkyldisulfanyl]alkyl]-phenyl]benzonitriles (CBnSSnCB), are reported. The alkyl fragment is varied from two to nine carbon atoms, and all eight homologues exhibit nematic behaviour. In addition, the dimer containing heptamethylene fragments (CB7SS7CB) exhibits a twist-bend nematic phase despite having an even-membered spacer. The values of the nematic–isotropic transition temperature, TNI, are higher for dimers containing an odd number of carbon atoms in each alkyl fragment. This surprising behaviour is interpreted in terms of the C-S-S-C torsion angle being around 88° that ensures that the molecular shape is bent irrespective of the parity of the alkyl fragments. For odd-membered fragments, however, the average shape is less bent and higher values of TNI are observed. The more uniform molecular curvature of CB7SS7CB accounts for the observation of the NTB phase. We also report the behaviour of two members of the 4-[4-[3-[2-[4-(4-cyanophenyl)phenyl]alkyldisulfanyl]-alkyl]phenyl]benzonitriles (CBnSmCB) which contain a thioether link embedded in the spacer. Both dimers exhibited nematic behaviour. The thioether link reduces the value of TNI compared to that of the dimer with an alkyl spacer. A much larger decrease in the nematic-twist-bend nematic temperature is observed and is attributed to a change in shape.

Gas kinetic schemes for solving the magnetohydrodynamic equations with pressure anisotropy

In many astrophysical plasmas, the Coulomb collision is insufficient to maintain an isotropic temperature, and the system is driven to the anisotropic regime. In this case, magnetohydrodynamic (MHD) models with anisotropic pressure are needed to describe such a plasma system. To solve the anisotropic MHD equation numerically, we develop a robust Gas-Kinetic flux scheme for non-linear MHD flows. Using anisotropic velocity distribution functions, the numerical flux functions are derived for updating the macroscopic plasma variables. The schemes are suitable for finite-volume solvers which utilize a conservative form of the mass, momentum and total energy equations, and can be easily applied to multi-fluid problems and extended to more generalized double polytropic plasma systems. Test results show that the numerical scheme is very robust and performs well for both linear wave and non-linear MHD problems.

Switching Chirality in Arrays of Shape-Reconfigurable Spindle Microparticles.

The giant circular photo-galvanic effect is realized in chiral metals when illuminated by circularly polarized light. However, the structure itself is not switchable nor is the crystal chirality in the adjacent chiral domains. Here spindle-shaped liquid crystalline elastomer microparticles that can switch from prolate to spherical to oblate reversibly upon heating above the nematic to isotropic transition temperature are synthesized. When arranged in a honeycomb lattice, the continuous shape change of the microparticles leads to lattice reconfiguration, from a right-handed chiral state to an achiral one, then to a left-handed chiral state, without breaking the translational symmetry. Accordingly, the sign of rotation of the polarized light passing through the lattices changes as measured by time-domain terahertz spectroscopy. Further, it can locally alter the chirality in the adjacent domains using near-infrared light illumination. The reconfigurable chiral microarrays will allow us to explore non-trivial symmetry-protected transport modes of topological lattices at the light-matter interface. Specifically, the ability to controllably create chiral states at the boundary of the achiral/chiral domains will lead to rich structures emerging from the interplay of symmetry and topology.

Fluorinated Poly(pentylene 4,4′-bibenzoate)s with Low Isotropization Temperatures and Unique Phase Transition Behavior

Fluorinated Poly(pentylene 4,4′-bibenzoate)s with Low Isotropization Temperatures and Unique Phase Transition Behavior

Enabling liquid crystal elastomers with tunable actuation temperature

Liquid crystalline elastomers are regarded as a kind of desirable soft actuator material for soft robotics and other high-tech areas. The isotropization temperature (Ti) plays an important role as it determines the actuation temperature and other properties, which in turn has a great effect on their applications. In the past, the common physical methods (e.g. annealing) to tune Ti is not applicable to tune the actuation temperature. The new Ti obtained by annealing immediately goes back to the old one once it is heated to a temperature above Ti, while actuation needs a temperature higher than Ti. For a fully cross-linked LCE material, once it is synthesized, the actuation temperature is fixed. Accordingly, the actuation temperature can not be tuned unless the chemical structure is changed, which usually needs to start from the very beginning of the molecular design and material synthesis. Here, we found that different Ti achieved by annealing can be preserved by reversible reactions of dynamic covalent bonds in covalently adaptable LC networks including LC vitrimers. Thus, a variety of soft actuators with different actuation temperatures can be obtained from the same fully cross-linked LCE material. As the tuning of Ti is also reversible, the same actuator can be adjusted for applications with different actuation temperature requirements. Such tuning will also expand the application of LCEs.

Mesomorphic Investigation of Binary Mixtures of Liquid Crystal Molecules with Different Mesogenic Architectonics

Different binary phase diagrams, made from two differently substituted three-rings azo/ester and azomethine/ester compounds of the same terminal alkoxy side chain of six carbons, as opposed to the other terminal polar substituent, which can either donate electrons or withdraw electrons including H. The thermal behavior of the prepared derivatives was investigated by differential scanning calorimetry and phases identified by polarized optical microscope. The first group of the binary mixtures was made from laterally F-substituted azo/ester derivatives and their laterally neat analogues. The second group of binary mixtures was made from laterally methoxy-substituted azomethine/ester derivatives and their laterally neat analogues. The final type of investigated phase diagrams was made from the laterally substituted azo and azomethine components bearing different lateral polar groups and different mesogenic moieties. Results were reviewed using phase diagrams that were produced and it was found that different mesomorphic characteristics were seen to depend on the mesogenic component as well as lateral and terminal polar groups. In all cases, these mixtures have been determined to have low melting-temperature eutectic compositions, while linear or negative deviation of nematic or smectic isotropic composition temperature dependence was observed.

THE CRYSTAL STRUCTURE OF La3Pb0.1Ga1.6Se7 AND Pr3Pb0.1Ga1.6Se7 COMPOUNDS

Samples of the stoichiometric composition La3Pb0.1Ga1.6Sе7 and Pr3Pb0.1Ga1.6Sе7, weighing 0.8 gram each, were prepared by fusing components of semiconductor purity in vacuumed quartz containers to a residual pressure of 10-2 Pa. The synthesis was carried out in a muffle furnace with software control of MP-30 technological processes. The maximum temperature of synthesis is 1100°C, homogenizing annealing lasted 240 hours at temperature of 500°C.&#x0D; The diffraction patterns for X-ray phase analysis were recorded at a DRON 4-13 diffractometer for 2Q range of 10-100° (CuKα radiation, scan step 0.02°, 20 s exposure in each point). Data processing and the determination of the crystal structure utilized WinCSD software package. Visualization of the crystal structure, stacking and coordination polyhedra was performed using the VESTA program.&#x0D; The crystal structure of the selenides La3Pb0.1Ga1.6Sе7 and Pr3Pb0.1Ga1.6Sе7 was studied by the X-ray powder diffraction method and its belonging to the hexagonal crystal system was established (space group P63). The refinement of atom coordinates and isotropic temperature displacement parameters in this model yielded satisfactory values of fit factors. Analysis of hkl reflex indices and their intensity indicates that the structural of La(Pr)3Pb0.1Ga1.6Sе7 compounds belong to the structural type La3CuSiS7 (space group P63; a = 1.028 nm, c = 0.575 nm)&#x0D; Crystal structure of selenides La3Pb0.1Ga1.6Se7 (a = 1.05595(4) nm, c = 0.63868(3) nm, RI = 0.0983, Rp = 0.1672) and Pr3Pb0.1Ga1.6Se7 (a = 1.03727(6) nm, c = 0.63772(5) nm, RI = 0.0868, Rp = 0.2286) was studied by X-ray powder method. It was established that the structure of the synthesized selenides belongs to the structural type La3CuSiS7 (SG P63; PS hP24). In their structure, R = La(Pr) atoms are localized in site 6c and, together with selenium atoms, form trigonal prisms with one additional atom [R 1Se13Se23Se3]. Atoms of statistical mixtures M1 (0.64 Ga + 0.09 Pb) and M2 (0.58 Ga + 0.11 Pb), concentrated in site 2a, form octahedra [M1 6Se2] and [M2 6Se2]. These octahedra are interconnected by faces and form columns in the direction of the c axis. The Ga (site 2b) atoms are surrounded by four selenium atoms. The formed tetrahedra are oriented in the direction of the c axis and are isolated from each other. Gallium-containing selenides La3Pb0.1Ga1.6Sе7 and Pr3Pb0.1Ga1.6Sе7 based on lanthanum and praseodymium are promising chalcogenides based on which materials for nonlinear optics and thermoelectricity can be created.&#x0D; Keywords: rare-earth metals; chalcogenide; crystal structure; X-ray powder diffraction.

Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission.

Two neutral copper(I) halide complexes ([Cu(BTU)2X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N'-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI-MS, elemental analysis, IR, and NMR spectroscopies (1H and 13C), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH…X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 × 10-7 S·cm-1 was achieved at 430 K for the chloro-complex and 1.37 × 10-6 S·cm-1 at 440K for the related bromo-complex.

Synthesis and characterization of semiconducting copper oxide nanoparticles and their impact on the physical properties of a nematic liquid crystalline material 4-pentyl-4′-cyanobiphenyl

Green synthesis of nanoparticles is a biological, eco-friendly and less expensive method which is free from chemical contaminants. In this work, copper oxide nanoparticles (CuO NPs) have been synthesized via green synthesis method. This method proved to be efficient for preparing CuO NPs at room temperature without using any inert atmosphere. The CuO NPs have been characterized using X-Ray Diffraction, Ultraviolet–Visible Spectroscopy and Fourier Transform Infrared Spectroscopy techniques which confirmed the proper synthesis of CuO NPs of the size 2–3 nm. Two different weight percents (0.2 and 0.5) of the synthesized CuO NPs have been dispersed in the nematogenic liquid crystalline material 4-pentyl-4′-cyanobiphenyl (5CB). The physical properties of pure 5CB and its nanocomposites were studied by differential scanning calorimetry, ultraviolet–visible spectroscopy and impedance spectroscopy. Thermodynamic and dielectric results show enhancement in the nematic to isotropic transition temperature of nanocomposites along with enhancement in conductivity as compared to its value for the pure 5CB. Through optical studies, the band gap has been estimated by the Tauc plots which suggest decrease in the optical band gaps of dispersed samples.

Ab initio predictions of the structural, electronic, optical, elastic, and thermoelectric properties of quasi-two-dimensional BaFZnP

We studied the structural parameters, elasticity, electronic structure, linear optical spectra, and thermoelectric coefficients of quasi-two-dimensional BaFZnP using ab initio methods. The computed equilibrium coordinates of atomic positions and lattice parameters were in good agreement with existing results. We derived numerical values for the elastic moduli and related physical parameters, such as the independent monocrystalline elastic constants, modulus of compressibility, modulus of shear, Poisson's ratio, Young's modulus, isotropic sound velocities, Debye temperature, ductility/brittleness nature, and elastic anisotropy. We examined the electronic properties including the energy band dispersions, density of states, and charge carrier effective masses, and concluded that BaFZnP is a semiconductor with a direct bandgap. The linear optical functions were explored in an energy window of 0–15 eV for incident electromagnetic waves polarized parallel to the [100] and [001] crystal directions. Numerical evaluation of the dependencies of the thermoelectric coefficients on charge carrier concentration and temperature shows that the thermoelectric characteristics of the p-doping BaFZnP are better than the corresponding ones of the n-doping BaFZnP over the charge carrier concentration range of 1016−1021cm−3. The p-doping BaFZnP with a hole concentration of around 1.81×1020 cm−3 possesses a figure of merit of 1.16 at 900 K, making it suitable for thermoelectric application.

INSTALLATION FOR DETERMINING THE THERMAL CONDUCTIVITY OF PLATES BY THE STATIONARY METHOD

When measuring the thermal conductivity of thermal insulation materials made by powder metallurgy and building porous materials, complications arise due to the fact that heat flows through the samples are commensurate with heat losses. The steady-state heat flow (SSHF) method is simple, does not require sophisticated equipment, and allows determining the thermal conductivity not in the near-surface layer but in the entire sample volume. Its disadvantage is low accuracy and the need to use reference samples. This work aims to develop an installation for measuring the thermal conductivity of largesized samples of low-conductivity material using the steady-state heat flow method with significantly higher accuracy than existing installations using this method. This is achieved by sandwiching the sample, which is a thin square plate of large dimensions, between the heater chamber and the refrigerator. The heating chamber is made of insulating material and its front wall, which is in contact with the sample, is made of the copper plate (which has good thermal conductivity). In the operating mode, the temperature in the heater chamber is maintained equal to the ambient temperature, which allows us to neglect heat losses and assume that in the steady-state mode, the heater power is equal to the heat flux through the sample. The thickness of the sample is much smaller than the size of its side (the sample should be square). This assumption is necessary to use the condition of isotropic temperature distribution in the cross-section of the sample. The refrigerator is filled with water and ice. The isotropic temperature distribution in the sample is ensured by its contact with the copper walls of the heater and refrigerator chamber. The temperature of the heated surface of the sample is measured using a thermocouple inserted through a hole in the front wall of the heater chamber. The proposed design of the installation and its operating conditions make it possible to significantly improve the accuracy of determining the thermal conductivity coefficient and make the error less than 2%.

Molecular structure and the twist-bend nematic phase: the role of spacer length in liquid crystal dimers

ABSTRACT The liquid crystal dimers, the 1-(4-substitutedazobenzene-4′-yloxy)-4-(4-cyanobiphenyl-4′-yl)butanes (CB4OABX), are reported in which the terminal substituent is either a methyl, methoxy, butyl, butyloxy, cyano or nitro group. The butyloxy spacer endows these dimers with the required molecular curvature to exhibit the twist-bend nematic phase in addition to showing the conventional nematic phase. Their transitional properties are compared to those of the corresponding dimers with either a pentyloxy or hexyloxy spacer. As expected, the even-membered pentyloxy-based dimers show the highest nematic–isotropic transition temperature, TNI, and exhibit smectic behaviour. These observations are attributed to their linear molecular shapes. The values of both the twist-bend nematic–nematic transition temperature, TN TB N, and TNI increase on passing from the butyloxy to hexyloxy spacer, but the change in TNI is greater than that in TN TB N. Thus, the ratio TN TB N is greater for the shorter spacer reinforcing the view that molecular curvature drives the formation of the NTB phase relative to the N phase. By comparison, the melting point decreases on passing from the butyloxy to hexyloxy spacer. Thus, increasing molecular curvature simultaneously increases both the melting point and NTB phase stability and this highlights the design challenge in obtaining dimers that exhibit enantiotropic NTB–I transitions.

The role of lateral substituent size in azobenzene chromophores on photo- and chiro-optical properties of photoactive polymethacrylates

Properties of functional liquid crystalline (LC) macromolecular materials, especially those showing self-organizing behaviour and targeted for specific purposes, strongly rely on the molecular structure of the mesogens used as side-chains. In order to get inside this relationship, new series of chiral LC polymethacrylates (PMA6Azo-R) with azobenzene groups having different lateral substituents (R), namely the methyl (-Me) and ethyl (-Et) groups on the central benzene ring, were synthesized and their comparative study was carried out. The synthesized polymers consist of photochromic azobenzene fragments that differ in the size of the lateral substituent (R = -H, -Me, -Et). All polymers exhibit the cholesteric phase, whereas the polymer without lateral alkyl group in addition forms the low-temperature SmĈ* phase. Investigations of the photoorientation process under linearly polarised visible light irradiation reveal that an increase in the size of side substituent considerably reduces the values of maximum achievable photoinduced dichroism (from 0.89 for PMA6Azo-H to 0.33 for PMA6Azo-Et that is associated with a decrease in the degree of mesogen anisometry). The effect of the lateral substituent size in azobenzene photochrome on the chiro-optical properties and mesomorphic behaviour of studied polymers was established. The presence of the lateral substituent in the photochrome/mesogen fragment leads to a significant decrease in isotropization temperature. Chiro-optical properties of the polymers and their photoswitching were studied, and it was found, that the introduction of the lateral substituent in the azobenzene fragment prevents the formation of exciton couples, that leads to a decrease in the circular dichroism (CD) values. UV irradiation and E-Z isomerisation of the azobenzene chromophores results in complete disappearance of CD signal; subsequent visible light irradiation does not lead to its full recovery. On the other hand, annealing of the films at temperatures higher than the glass transition almost fully recovers the initial CD values. The designed polymethacrylates can be considered as promising materials for various photonic applications.

Metal oxide alumina nanowire-induced polymer-dispersed liquid crystal composites for low power consumption smart windows

Herein, polymer dispersed liquid crystals (PDLCs) based smart windows are proposed using a host thiol-ene-based UV curable photopolymer and nematic liquid crystals (E7). The proposed PDLC was prepared by polymerization-induced phase separation technique. PDLCs were doped with alumina nanowires (ANWs) in different concentrations and investigated their dispersion effect on various physical properties. An increase in nematic to isotropic transition temperature was observed in ANWs doped PDLC nanocomposite. Reduction in threshold and saturation voltages by 62.5% (1.5 V) and 56.57% (16.5 V), at 1.0 and 0.25 wt.% of doped ANWs respectively in PDLC was noticed. This reduction could be attributed to an increased electric field caused by lowering medium resistivity and increased cell capacitance. A decrease in dielectric anisotropy with temperature and ANWs doping in all samples was also observed. The maximum absorbance for 0.5 wt.% ANWs doping in PDLC at a wavelength of 511 nm were observed. The electric field-induced results indicate that the proposed ANWs doped PDLC composite film can operate at a much lower voltage (19.5 V) and show improved transparency. These findings may assist to develop fast-switching smart windows and other energy-saving devices.

Electron heating mechanisms at quasi-perpendicular shocks – revisited with magnetospheric multiscale measurements

ABSTRACTWe demonstrate that measurements obtained from NASA’s magnetospheric multiscale (MMS) mission support quasi-adiabatic electron heating in quasi-perpendicular shocks with temperature Te⊥ ∝ B1 + α, where B is the magnetic field strength and α represents departure from adiabaticity. Adiabatic heating (α = 0) results from the conservation of magnetic moment on spatially increasing magnetic field inside the shock ramp. Negative α &amp;lt; 0 is observed in most situations, where perpendicular energy gain from adiabatic heating is redistributed by interactions with waves to the parallel direction leading to a lower isotropic temperature increase. Positive α is observed when the stochastic heating of electrons is activated by the E × B wave acceleration mechanism by electrostatic waves leading to a higher temperature increase. By using test-particle simulations in a realistic shock model we have elucidated the process of stochastic wave acceleration. We have also shown the equivalence of adiabatic heating and acceleration by gradient B drift at shocks with low Mach numbers and demonstrated that the cross-shock potential does not contribute to the electron heating. Signatures of quasi-adiabatic heating and/or stochastic heating of electrons are observed in all shocks analysed with measurements by the MMS.

Synthesis, Structural and Theoretical Analyses of C≡N···I Halogen-Bonded Liquid Crystalline Complexes of 4-Cyano-4′-alkoxy Biphenyl Systems

A series of 4-cyano-4′-alkoxybiphenyl compounds were synthesized by varying the spacer chain lengths (−CH2−)n, where n = 3–10, for the systematic study of a halogen-bonded (XB) complex with 1,4-diiodotetrafluoro benzene. The XB liquid crystalline complexes obtained from the liquid-assisted grinding method were characterized by FTIR, Raman, DSC, and PXRD studies. Further, C≡N···I XB interaction was established by single-crystal X-ray diffraction analysis. The odd-even analysis has suggested that the even carbon chain length containing XB liquid crystalline complexes shows slightly higher alteration in their isotropic temperature compared to the odd carbon chain lengths of such complexes. Furthermore, it is interesting to note that the higher alkyl chain complexes (n = 6–10) showed liquid crystalline temperature at lower values with respect to their ligands. The Hirshfeld and energy framework analyses have also been carried out to assess the stability and percentage contribution of XB noncovalent interaction. The frontier molecular orbital, noncovalent interaction, molecular electrostatic potential, and QTAIM analysis were performed using DFT to evaluate the nature of XB in these halogen-bonded liquid crystalline systems.

Photo/heat/electricity/pressure-driven photonic pattern with multimode memory effect

The multimode memory effect of cholesteric liquid crystals (CLCs) photonic patterns has promising applications for the development of optical sensors, responsive colour decors, and camouflaging techniques. The present memory pattern is mainly aroused from the elastic effect of the polymer network or bistability of the CLC, it is desired for the development of alternative memory mode in non-polymerizable system, which may be helpful for the recyclable use of LC materials for the expired pattern. There remains a challenge for designing photonic patterns with multimode memory effects in a non-polymerized system owing to the limited availability of responsive materials. Herein, photo/heat/electricity/pressure multimode photonic memory pattern was firstly fabricated from non-polymerized cholesteric LC by mixing host LC E7, axially chiral azobenzene-based molecules (ACAMP), and S-form chiral dopants (S5011) based on the combination of PVA alignment layer and photoisomerization of ACAMP. The formed photonic patterns can be reversibly hidden/reappear by controlling the ambient temperature above/below the isotropic temperature or applying combined stimuli of electricity/pressure. The multi-memory pattern from the non-polymerizable system is friendly-environmental (recyclable use) with the simultaneous colour-change of the pattern and background under external stimulus. This study provides new insights into the development of multiresponsive nanostructures with tailorable functionalities, thus presenting new applications in diverse fields ranging from display technologies to information communication.