LC Properties Research Articles

Recommendations to address uncertainties in environmental risk assessment using toxicokinetic-toxicodynamic models

Providing reliable environmental quality standards (EQSs) is a challenging issue in environmental risk assessment (ERA). These EQSs are derived from toxicity endpoints estimated from dose-response models to identify and characterize the environmental hazard of chemical compounds released by human activities. These toxicity endpoints include the classical x% effect/lethal concentrations at a specific time t (EC/LC(x, t)) and the new multiplication factors applied to environmental exposure profiles leading to x% effect reduction at a specific time t (MF(x, t), or denoted LP(x, t) by the EFSA). However, classical dose-response models used to estimate toxicity endpoints have some weaknesses, such as their dependency on observation time points, which are likely to differ between species (e.g., experiment duration). Furthermore, real-world exposure profiles are rarely constant over time, which makes the use of classical dose-response models difficult and may prevent the derivation of MF(x, t). When dealing with survival or immobility toxicity test data, these issues can be overcome with the use of the general unified threshold model of survival (GUTS), a toxicokinetic-toxicodynamic (TKTD) model that provides an explicit framework to analyse both time- and concentration-dependent data sets as well as obtain a mechanistic derivation of EC/LC(x, t) and MF(x, t) regardless of x and at any time t of interest. In ERA, the assessment of a risk is inherently built upon probability distributions, such that the next critical step is to characterize the uncertainties of toxicity endpoints and, consequently, those of EQSs. With this perspective, we investigated the use of a Bayesian framework to obtain the uncertainties from the calibration process and to propagate them to model predictions, including LC(x, t) and MF(x, t) derivations. We also explored the mathematical properties of LC(x, t) and MF(x, t) as well as the impact of different experimental designs to provide some recommendations for a robust derivation of toxicity endpoints leading to reliable EQSs: avoid computing LC(x, t) and MF(x, t) for extreme x values (0 or 100%), where uncertainty is maximal; compute MF(x, t) after a long period of time to take depuration time into account and test survival under pulses with different periods of time between them.

“Effect of the linking unit on the calamitic-shaped liquid crystal: a comparative study of two homologous series of benzoate and cinnamate linked compounds”

Two homologous series based on three linking groups have been synthesized and well characterized by elemental analyses and spectroscopic techniques such as Fourier transform infrared [FT-IR] and proton magnetic resonance magnetic resonance [1H NMR] spectroscopy. The mesomorphic properties of these compounds were observed by using optical polarized microscopy (POM) and confirmed by differential scanning calorimetry (DSC) analysis. In this present investigation, we have synthesized two homologous series viz. (E)-4-(3-(4-(tetra decanoyloxy) phenyl) acryloyl) phenyl-4-n-alkoxy benzoate (Series-1) and 4-((E)-3-(4-(((E)-3-(4-n-alkoxy phenyl) acryloyl) oxy) phenyl)-3-oxo prop-1-en-1-yl) phenyl tetradecanoate (Series-2). Both of the series are differing with respect to the first linking group. All the homologous in following series displays LC properties on heating as well as cooling condition except first four homologous (C1 to C4) in series-1 and six homologous (C1 to C6) in series-2. To get more insights, the HOMO, LUMO studies are carried out which supports intramolecular charge transfer interactions in this class of mesogens.

Hydrogen-bonded LC nanocomposites: characterisation of nanoparticle-LC interactions by solid-state NMR and FTIR spectroscopies

ABSTRACTAlthough the molecular-level nanoparticle-liquid crystal (NP-LC) interactions are key for forming stable NP dispersions in LC, characterisation of these interactions is scarce in the literature. Recently, we have developed hydrogen-bonded LC nanocomposites based on mesogenic carboxylic acids and NPs functionalised with hydrogen-bond acceptor/donor groups. Here, we apply solid-state 1H and 13C NMR and Fourier transform infrared spectroscopies to model systems consisting of mixtures of trans-4-n-butylcyclohexanecarboxylic acid (4-BCHA), 4-hexylbenzoic acid (6BA) and 4,4ʹ-bipyridine. The binary mixture, 4-BCHA:6BA, was also studied. The results were compared to monolayer quantities of 6BA and 4-BCHA adsorbed on pyridine functionalised zirconia NPs (ZrO2-n3-pyridine) to understand the different effects of the functionalised NPs on the LC properties.

Tailored Colloidal Stability and Rheological Properties of Graphene Oxide Liquid Crystals with Polymer-Induced Depletion Attractions.

Graphene oxide liquid crystallinity (GO LC) has been widely exploited for high-performance graphene-based applications. In this regard, colloidal stability of GO LC suspension is a crucial requirement, particularly while polymers are often added to the GO LC. Unfortunately, current level of knowledge on how polymers influence the structure and properties of GO LC is not sufficient to systematically guide the development of applications. Here, we investigate the microstructure and rheological properties of GO LC suspensions in the presence of polymer additives with varying molecular weights and concentrations. Similar to conventional colloidal systems, non-negligible polymer-induced interactions are found in GO LC suspensions, which can effectively modulate the interaction among GO platelets and the relevant physical properties. On the basis of extensive small-angle X-ray scattering and rheological measurements, we demonstrate that, contrary to the general perception, polymer-induced depletion attraction can increase the colloidal stability of GO, while also preventing the vitrification of GO LC. In addition, a proper level of polymer additive can reduce the viscosity of GO LC suspensions by orders of magnitude, providing an effective route to GO LC-based solution processing. After all, the colloidal stability and rheological properties of GO can significantly impact the quality of GO. Therefore, we believe that our finding will be of great interest in the field of graphene-based applications, as it presents effective strategies for improving properties.

Supramolecular columnar self-assembly of wedge-shaped rhodanine based dyes: Synthesis and optoelectronic properties

The development of small π-conjugated functional organic molecules capable of forming supramolecular columnar self-assembly, is a rapidly growing area of material research. In this context, the present work describes the design and synthesis of a new series of wedge-shaped rhodanine derivatives with D-A configuration, viz.RA1–RA5. Their LC properties were studied by employing DSC, POM and XRD techniques. The mesophase behavior was investigated as a function of chain length, density and position of alkoxy terminals to understand structure-property relationship. Interestingly, the longer chain analog, i.e.RA3 demonstrated H-bonded disc-like macrocyclic structures, causing an imperative columnar hexagonal phase at ambient temperature. Further, their photophysical and electrochemical properties were evaluated. They showed a good dye property attributing to effective intramolecular interactions, as confirmed by experimental and theoretical studies. Conclusively, RA3 has been considered to be a potential candidate for its application in organic electronics.

The induction of the Ntb phase in mixtures

ABSTRACTWe report the induction of the Ntb phase over a wide temperature and concentration range in a binary system. This was achieved by addition of a flexible dopant without LC properties to a flexible dimer exhibiting only a nematic LC phase. The Ntb phase was identified by Polarising Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD) techniques.

Preparation, spectral and thermal properties of new Isoflavone derivatives: mesomorphic properties and DFT studies

ABSTRACTThe four new homologous series of symmetric Isoflavon dimers were synthesised using varied alkyl/aryl diamines in linear sense. The chemical structures of the molecules were characterised by IR, NMR and CHNS analysis. Further, Liquid crystalline properties were verified using the combination of differential scanning calorimetry (DSC) and polarised optical microscope (POM). The molecular systems studied here reveal that LC property depends on the length of the middle connecting diamine spacer along with terminal alkyl spacer. The lower members favour to exhibit smectic A phase, whereas higher members exhibit nematic mesophase. The nature of LC property behaviours is supported by molecular geometries studied by DFT calculations.

Self-assembly, conductivity and chemosensor behavior of biphenylsulfone based Janus polycatenar

A novel Janus polycatenar JP-I bearing a bisphenylsulfone central core, with a hydrophobic 3,4,5-tridodecyloxybenzylether unit at one side and a hydrophilic trioligoethylene oxide benzyl triazoly unit at another side has been synthesized via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. JP-I can display SmA2 phase triggered by the addition of alkali metal ions. The LC property of the doped system was well demonstrated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) experiments. The conductivity of the doped system (JP-I:LiOTf) is 4.0 × 10−8 S cm−1. JP-I could gel both in ethanol and aqueous ethanol. Such gel which formed in ethanol showed a helical nanostructure. The XRD displayed that the JP-I could self-assemble into a monolayer structure which had a small tilt angle in the layers. Furthermore, the gel system could be established to remove iodine from water. Additionally, JP-I could recognize Fe3+ with lower detection limit in aqueous ethanol. Finally, JP-I could self-assemble into micelles in aqueous solution and the critical micelle concentration CMC was determined to be 0.002 mg/ mL with the diameter of the spherical micelles about 15–20 nm.

Mesomorphism dependence on central bridge and tail ended polar group

A novel azoester homologous series of laterally and terminally substituted viz, RO–C6H4–CH=CH–COO–C6H3–(CH3) –N=N–C6H4–Cl is synthesized, characterized and studied with a view to understand and establish the relation between molecular structure and thermotropic liquid crystalline property of its homologs. Series consists of twelve homologs. LC properties commence from very first member of a series and continue up to last homolog as enantiotropic nematic with absence of smectic property even in the monotropic condition. Transition temperatures of homologs were determined by polarizing optical microscopy equipped with a heating stage. The transition curves Cr?N and N?I behaved in normal manner. Thermal stability for nematic is 196.7?C whose mesophaselength ranges from 35°C to 131°C.

Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumichrome ions (M = Li-Cs) in the gas phase.

The photochemical properties of flavins depend sensitively on their environment and are strongly modified by coordination with metal ions. Herein, the electronic spectra of cold complexes of the smallest flavin molecule (lumichrome, LC, C12N4O2H10) with alkali ions (M+LC, M = Li-Cs) are measured by photodissociation in the visible range (VISPD) in a cryogenic ion trap coupled to a tandem mass spectrometer and an electrospray ionization source. The observed vibronic spectra of all ions are assigned to the optically bright S1 ← S0 (ππ*) transition of the most stable O4 isomer of M+LC by comparison with quantum chemical calculations at the PBE0/cc-pVDZ level coupled to multidimensional Franck-Condon simulations. The rich vibronic spectra indicate substantial geometry changes upon S1 excitation. Large red shifts of the S1 origins upon metal complexation and progressions in the intermolecular in-plane metal stretch and bend modes demonstrate that the strength of the metal-flavin interaction in M+LC(O4) strongly increases by S1 excitation. The stronger M+LC bond in the S1 state of M+LC(O4) is rationalized by the charge reorganization upon ππ* excitation of the LC chromophore. The computations confirm that the optical properties of LC can be strongly modulated by metalation via both the type and binding site of the metal ion.

Characterisation of Lactococcus lactis isolates from herbs, fruits and vegetables for use as biopreservatives against Listeria monocytogenes in cheese

The control of Listeria monocytogenes in soft cheese manufacture remains a challenge due to its widespread occurrence, ability to grow at refrigerated temperatures and salt resistance. The application of antimicrobial compounds produced by lactic acid bacteria (LAB) as natural preservatives for improving cheese quality and safety has attracted significant research interest. The aim of this study was to select non-dairy origin LAB strains with anti-Listeria activity and to characterise their industrially relevant properties for potential roles as biopreservative adjunct cultures for use in cheese production. A total of 897 LAB isolated from herbs, fruits and vegetables were screened for their anti-Listeria activity using an MRS agar overlay assay. Fourteen isolates with strong activity were identified by 16S rRNA gene sequencing as Lactococcus lactis and all contained the nisin gene cluster. Of these fourteen isolates, four strains also showed detectable anti-Listeria activity in a milk medium. These wild Lc. lactis strains possessed slow lactose utilisation and acidification capacity in milk despite exhibiting high growth rates. This was likely due to the adoption of the mixed acid fermentation pathway since ethanol was a major metabolic end product. Analysis of volatiles in milk and laboratory scale cheese fermented with wild and industrial Lc. lactis strain combination using headspace solid phase microextraction (SPME) GC-MS identified up to a 300–400 fold increase in the production of 3-methylbutanal, an important cheese odorant with a malty flavour. Whole genome sequencing of four wild strains provided some genetic insights into their phenotypes. The wild Lc. lactis lack the lactose utilisation operon (lacABCDFEG) commonly found in industrial strains, but contain genes encoding a putative β-galactosidase and a previously characterised alternative lactose assimilation pathway with slow lactose uptake. Wild strains also contain genes encoding α-keto-acid decarboxylase (kdcA) required for 3-methylbutanal production. These results provide insight into technological properties of wild non-dairy Lc. lactis strains which could be potentially used as biopreservative adjunct cultures to control the growth of L. monocytogenes in cheese.

Thermal and phase transformation behavior of epoxy‐functional graphene oxide/liquid crystalline epoxy composite

In this study, epoxy‐functional graphene oxide/liquid crystalline epoxy (efGO/LCE) composite was obtained by mixed LCE with efGO, which was obtained by modifying graphene oxide (GO) with LCE in alkaline condition. The influence of efGO content on glass transition temperature (Tg), thermal stability, and phase transformation behaviors of the composite were characterized by thermogravimetric analysis, differential scanning calorimetry, and polarized optical microscopy. The results reveal that the right amount of efGO can keep the LC property of LCE while GO inhibits the formation of LC phase of LCE. POM photographs of efGO/LCE composites show clear bright specks under polarized light, suggesting heterogeneous nucleation effects is in favor of formation of LC phase. Moreover, the initial decomposition temperature of efGO/LCE composite is increased to 380°C from that of pure LCE at 350°C when efGO content is 1 wt%. It suggests that efGO is effective to increase thermal decomposition temperature and glass transition temperature (Tg) due to cross‐linking between efGO and LCE. POLYM. COMPOS., 39:E1391–E1397, 2018. © 2017 Society of Plastics Engineers

Mesomorphism dependence on molecular rigidity and substitution of same functional group on lateral or terminal position of tailed phenyl ring

ABSTRACTNovel liquid crystal materials (LCs) of low temperature range (53°C to 75°C) have been synthesized through a series of chalconyl derivatives consisting of two phenyl rings bonded through a –CH˭CH‒CO‒ central bridge to study the effect of molecular structure on LC properties in general and with a focus on molecular rigidity. The novel homologues series (C1 to C18) consists of thirteen homologues with general formula RO‒C6H4‒CH˭CH‒CO‒C6H4‒OC10H21(n) (meta). The C1, C2, C3 homologues are nonliquid crystals (NLC) and the rest of the homologues (C4 to C18) are either monotropic or enantiotropic liquid crystals. C4 to C6 homologues are enantiotropicnematic and the rest of the mesomorphic homologues are (C7 to C18) monotropicsmectic in addition to monotropicnematic character. Transition and melting temperatures including textures of homologues were determined by an optical polarizing (POM) microscopy equipped with a heating stage. Textures of a nematic phase are threaded or Schlieren, and that of the smectic phase are of the type Smectic A or C as judged directly from the heating top of the microscope. Thermal stability for smectic is very poor and of the nematic is (N-I) 69.3°C whose, total mesophase length ranges between 07.0 to 14.0°C at C8 and C4 homologues respectively.

Switchable Fresnel lens based on hybrid photo-aligned dual frequency nematic liquid crystal

In this article we disclose a method to fabricate a polarization independent dual frequency liquid crystal (DFLC) Fresnel lens (FL) with relatively high efficiency. The switchable FL is based on a patterned hybrid photo-aligned nematic (HPAN) DFLC cell assembled by one substrate providing the homeotropic anchoring and the other one providing the in-plane patterned alignment, with mutually orthogonal easy axis in the neighboring alignment domains, which has been prepared by means of two-step photo-alignment technique. Due to the electro-optical properties of dual frequency LC, the proposed HPAN DFLC FL, which manifests relatively high diffraction efficiency of 38.5% and low driving voltage, has the possibility of achieving a fast response by alternatively switching between high frequency and low frequency electric fields. Thus, with an excellent rewritable performance leading to the alternative focus/defocus switch, the HPAN DFLC FL would definitely be practical and promising in many modern devices.

The effect of geometrical shape and molecular rigidity on mesomorphism

ABSTRACTA novel nonlinear homologous series RO‒C6H4‒CH˭CH‒COO‒C6H4 (meta) ‒CO‒CH˭CH‒C6H4‒OC12H25(n) (para) consisting of three phenyl rings, two central bridges ‒CH˭CH‒COO‒ and ‒CO‒CH˭CH‒ as well as ‒OR and ‒OC12H25(n) as flexible and constant terminal end groups respectively. The object in view is aimed to understand and establish the effect of molecular structure on LC properties of nonlinear inverted “V” shaped molecules. Novel homologous series consists of thirteen homologues. Transition temperatures and textures were determined by polarizing optical microscopy (POM) equipped with a heating stage. Textures of nematic phases are threaded or schlieren and that of a smectic phases are of the type-A or C. Transition curves of a phase diagram behaved in a normal manner. Sm-N and N-I transition curves exhibited odd-even effect. Analytical, Thermal and Spectral data confirms the molecular structure of homologues.

Role of specific and nonspecific intermolecular interaction in electro-optical response of doped 6CHBT nematic liquid crystal with azo dyes

Investigations done so far have shown that dopant material have a considerable effect on the electro-optical responses of dye-doped liquid crystal. But the type of inter or intra-molecular interaction roles in electro-optical properties and nonlinearity of doped liquid crystalline systems has uncovered. In this work, to study of the kind of molecular interaction effects on electro-optical properties of doped LC, two dyes with dissimilar interactional and functional groups were used as LC dopants. Therefore, doping these dyes into liquid crystals allows us to understand and analyze the effect of interaction type on electro-optical responses of the pure and doped samples. The electro-optical Kerr behavior, the pre-transition temperature and third order nonlinear susceptibility of pure and doped LC by two dyes with different interactional groups were having studied. The obtained results revealed that the electro-optical response of nematic liquid crystal can be strongly enhanced or decreased, depending on dopant's nature, concentration and type of specific and nonspecific interaction between doped dye and liquid crystal molecules. In other words, it will be shown that dopants molecular interactions with each other and liquid crystal molecules are important factors for controlling of electro-optical responses of dye doped liquid crystal system.

New mesogenic compounds possessing a biphenyl ester and ether moiety comprising 1,3-dimethylbarbituric acid: synthesis, characterisation and mesomorphic studies

ABSTRACTNew substituted derivatives of 5-vinyl-1,3-dimethylbarbituric acid were synthesised and evaluated for liquid crystal properties. Two sets of molecules were prepared. One end of all the molecules possesses the 1,3-dimethylbarbituric core. The first set comprises biphenyl ethers, 4a–n and the second set biphenyl esters, 5a–g. Liquid crystalline properties were investigated by POM and DSC techniques. All the compounds exhibited enantiotropic smectic A and nematic mesophases. The LC properties were found to depend on the spacer and terminal alkoxy- chain and alkoxy- ester moiety of the molecules. Smaller alkyl chain members showed a smectic phase, while higher alkyl chain members showed a nematic phase.

Synthesis mesomorphic and theoretical studies of some new unsymmetrical dimeric ethers of 6-amino-1,3-dimethyluracil and biphenyl cores

New sets of unsymmetric calamitic molecules with uracil unit at one end and biphenyl core at another end were synthesized. Liquid crystal property of these molecules was investigated by POM and DSC techniques. All compounds exhibit LC property depending on the spacer and terminal alkoxy chain of the molecules. First set shows smectic phase in lower members and nematic phase appeared in higher members. The second set favour nematic liquid crystalline phase with respect to spacer alkyl chain length. Molecules are escaped from the planarity as a result disturbing the layer stacking leads to nematic phase in higher analogues. Theoretical studies have been performed for all the compounds and are found to be in agreement with the results of the current studies.

Mesomorphic properties of chiral three-arm liquid crystals containing 1,2,4-butanetriol as core

A series of symmetric and asymmetric three-arm liquid crystals (TALCs) of which the molecular structure with a central core of 1, 2, 4-butanetriol attached by three rod-like mesogenic moieties have successfully been synthesized. The rod-like mesogenic side arms are 4′-(4-(trifluoromethyl) benzoyloxy) biphenyl-4-carboxylic acid (TFBA) and 4′-(4-(allyloxy) benzoyloxy) biphenyl-4-carboxylic acid (AOBA), respectively. BTA0 and BTA3 are symmetric TALCs with three TFBA or three AOBA as LC side arms, respectively. BTA1 is an asymmetric TALC with one AOBA and two TFBA as side arms. BTA2 is an asymmetric TALC with two AOBA and one TFBA as side arms. The chemical structures and LC properties of the LC side arms and TALCs were characterised by FTIR, 1H NMR, elemental analysis, DSC, TG, POM and X-ray diffractometer. TFBA displayed smectic B (SmB) phase, AOBA exhibited nematic (N) phase. The TALCs all displayed chiral mesophase properties. BTA0 displayed chiral smectic C (SmC∗) mesophase. BTA1, BTA2 and BTA3 exhibited cholesteric (ch) mesophase. In addition, a chiral smectic A (SmA∗) mesophase was observed for BTA1. The results indicated that the 1, 2, 4-butanetriol is vital in inducing chiral mesophase of the TALCs. The side arms also played an important role in the mesophase type and mesogenic region. The TALCs displayed cholesteric mesophase when nematic LC side arm AOBA was introduced into the chiral core. The mesogenic region of the TALCs increased with the content of the wide-mesophase-region LC side arm AOBA introduced into the TALCs increasing. The melting temperature and the clear temperature of the TALCs were lower than those of the LC side arms (TFBA and AOBA). The mesophase regions of the TALCs were wider than those of the LC side arms.

Влияние димеризации молекул азокрасителей на свойства систем ЖК-краситель при взаимодействии с лазерным излучением

Влияние димеризации молекул азокрасителей на свойства систем ЖК-краситель при взаимодействии с лазерным излучением