Synthesis and mesomorphic properties of some ferroelectric liquid crystals of lactate

A semiperfluorinated chain has been introduced into three series of lactate‐based molecules, and their mesomorphic properties have been studied by DSC and optical polarized microscope. An abnormal phenomenon has been found that the introduction of a triple bond in the core of the molecule, which lengthened the molecule, gave rise to a decrease in the thermal stability of chiral smectic C phase and smectic A phase. 2, 3‐Difluoro substituents of the phenylenic structure hinder the formation of the chiral smectic C phase because of the steric effect.     

Synthesis and mesomorphic behavior of benzothiazole-based liquid crystals having terminal methoxyl group

A homologous series of benzothiazole derivatives, 6-methoxy-2-(4-alkanoyloxybenzylidenamino)benzothiazoles, were synthesized and characterized using FT-IR, ¹H and ¹³C NMR, mass spectrometry and elemental analysis. Enantiotropic nematic phase was observed throughout the entire series. Smectic C phase only emerged from the decanoyloxy derivative onwards. The terminal methoxyl group and the ester linkage influenced the mesomorphic behavior of the present series.     

Synthesis and mesomorphic evaluation of new calamitic liquid crystals containing benzothiazole core

The design and synthesis of new calamitic benzothiazole-based liquid crystals,2-[4-（4-alkyloxybenzoyloxy）-phenyl]ben-zothiazoles are presented.The target compound was characterized using spectroscopic techniques,such as FT-IR,NMR(¹H and ¹³C),microanalysis and EI-MS.The liquid crystalline behaviours of these compounds were thoroughly examined by differential scanning calorimetry and polarizing optical microscope techniques.These materials exhibited enantiotropic nematic phase with high thermal stability（>168℃）.Smectic A phase starts to emerge as monotropic（metastable） phase from C10 member and changes into enantiotropic（stable） phase from C12 and persists up to C16 members.     

Mesomorphic behavior of new benzothiazole liquid crystals having Schiff base linker and terminal methyl group

正A homologous series of heterocycles,6-methyl-2-(4-alkoxybenzylidenamino)benzothiazoles,were synthesized and characterized using FT-IR,~1H and ~(13)C NMR and mass spectrometric analysis.Enantiotropic nematic phase was observed for shorter members.Smectic A phase only emerged from octyloxy derivative onwards.The terminal methyl group at the benzothiazole fragment and the Schiff base linkage influenced the mesomorphic behavior of the present series.     

Computer simulation of liquid crystals

Summary We review recent progress in the computer simulation of liquid crystals, with special emphasis on hard particle models. Surprisingly, the simplest molecular models, taking account only of molecular size and shape, are sufficient to generate a wide variety of liquid crystalline phases, closely analogous to those observed in real life. Thermodynamic stability of different phases is very sensitive to shape, and presumably will also be sensitive to further details of intermolecular interactions as they are incorporated into the model. Realistic atom-atom potential models of liquid crystals are available, but the associated simulations are quite expensive. Thus, while idealized models may be used to study quite general, fundamental properties of mesophases, the modelling of specific liquid crystal systems in a realistic way remains a great challenge. Progress continues to be made on both these fronts.     

Mesomorphic behaviour of new azomethine liquid crystals having terminal bromo substituent

A homologous series of azomethine esters,4-n-alkanoyloxybenzylidene-4’-bromoanilines possessing even number of carbon atoms at the terminal alkanoyloxy chain(C_n-1H_2n-1COO- n = 8,10,12,14,16,18) was synthesized and characterized.Whilst n-octanoyloxy to n-dodecanoyloxy derivatives exhibited enantiotropic smectic A and smectic B phases,n-tetradecanoyloxy to n-octadecanoyloxy derivatives possessed enantiotropic smectic A and monotropic smectic B properties.n-Decanoyloxy derivatives demonstrated the optimum exhibition for both smectic A and smectic B phases.It was found that the length of terminal alkanoyloxy chain has an influence on mesomorphic properties.     

Highly fluorinated liquid crystals with wide nematic phase interval and good solubility

A series of new liquid crystal compounds with both ethylene and difluoromethyleneoxy linking groups have been synthesised and their physical properties were measured. The compounds exhibit lower melting points and broader nematic mesophase temperature range than that of corresponding four-rings compound. Their anisotropic properties are Δε of about 25 and Δn of 0.135. The investigation shows that their solubilities are much better than that of reference compound. A mixture made by equivalent mass ratio of the compounds with side chain of ethyl, propyl and pentyl is found to keep nematic phase from 12°C°C to 109°C, which is rarely observed in highly fluorinated liquid crystals.     

Terahertz properties of fluorinated liquid crystals

In this article, optical properties of four fluoro-substituted 4-propyl-4′-[(4-ethylphenyl)ethynyl] biphenyls and liquid crystal mixture A are presented in the terahertz (THz) range. Birefringence, refractive indices and absorption coefficients for ordinary and extraordinary ray of liquid crystals are described in the range of 0.3 to 3.0 THz. It shows that the measured parameters are dependent on the number and placement of fluorine atoms in the molecules. Measurements have been performed using time-pulsed spectroscopy.     

Mesomorphic behavior of new azomethine liquid crystals having terminal iodo group

A series of azomethine esters,3-hydroxy-4-{[（4-iodophenyl）imino]methyl}phenyl alkanoates possessing even number of carbon atoms at the terminal alkanoyloxy chain(C_n-1H_2n-1COO-,n = 4,6,8,10,12,14) was synthesized.n-Butanoyloxy was found non-mesogenic,whilst n-hexanoyloxy to n-tetradecanoyloxy exhibited enantiotropic smectic A phase with fan-shaped texture.It was found that the length of terminal alkanoyloxy chain influenced the mesomorphic properties.     

新型含氟液晶类化合物的质谱研究

本文报道66个新型含氟液晶类化合物的电子轰击电离质谱(EIMS). 66个化合物分为三个类型, 即炔醚类, 炔酯类和炔类. 并利用MS/MS联用技术和高分辨质谱(HRMS)数据研究了三种不同类型化合物的裂解机理, 并总结其规律性, 结果将有助于未知的类似化合物的结构鉴定 .     

Polarisation-dependent dielectric processes in ferroelectric liquid crystals

The behaviour of dielectric relaxation process has been investigated in four ferroelectric liquid crystal (FLC) materials having different spontaneous polarisation (Ps) values. Ps effect on the permittivity in four different FLCs has been carried out in highly anchored sample cells around ~8 μm thick. It has been found that the main contribution to the dielectric permittivity in chiral Smectic C (SmC*) phase is due to Goldstone mode (GM) and partially unwound helical mode (p-UHM). In higher PS value FLC materials, the p-UHM process is found to dominate the dielectric properties. It has also been observed that p-UHM process is highly dependent on the probing ac voltage and temperature, whereas GM is found to be weakly dependent of probing voltage and temperature in SmC* phase of all the studied FLC materials. The influential contribution of p-UHM has exhibited the dielectric properties in its intrinsic frequency range making the materials suitable for futuristic display and photonics devices.     

Reinvestigation of liquid crystalline property of dimesogenic compound consisting of cholesterol and cyanobiphenyl

The dimesogenic compound consisting of cholesterol and cyanobiphenyl mesogens interlinked byω-oxyalkanoyl spacer was synthesized.The mesomorphic properties were investigated by differential scanning calorimetry(DSC),polarizing optical microscopy(POM),and X-ray diffraction(XRD).The experimental results indicated that this compound exhibited mesophase over a much wider temperature range and a new mesophase blue phase(BP).Focal conic domains(FCDs) and droplets texture to the smectic A phase(SA),oily streaks...     

Synthesis of deuterium-labelled, optically active, ferroelectric liquid crystals

The synthesis of two selectively deuterium-labelled 4-(((S)-1-((S)-1-((S)-2-methylbutoxy)-1-oxopropan-2-yloxy)-1-oxopropan-2-yloxy)carbonyl)phenyl 4′-(heptyloxy)biphenyl-4-carboxylate derivatives is reported. A new preparation strategy was developed in order to optimise the yields as well as the optical purity, this property being of fundamental importance for the optical applications of this ferroelectric liquid crystal.     

Smectic A liquid crystals from dihydrazide derivatives with lateral intermolecular hydrogen bonding

Six dissymmetrical dihydrazide derivatives, N-(4-alkoxybenzoyl)-N′-(4′-nitrobenzoyl) hydrazine (Cn-NO₂) and N-(4-alkoxybenzoyl)-N′-(4′-biphenyl carbonyl) hydrazine (Cn-Ph), were synthesized and investigated by means of differential scanning calorimetry, polarized optical microscopy and wide angle X-ray diffraction. The compounds exhibit smectic A₁ phase. Based on the results of ¹H NMR and variable temperature FT-IR spectroscopy, lateral intermolecular hydrogen bonding between -CO and -N-H groups was proposed and the effect of hydrogen bonding on the phase transitions was discussed. It was concluded that the combination of lateral intermolecular hydrogen bonding and microphase segregation stabilized the smectic A phase.     

Highly fluorinated monomers precursors of side-chain liquid crystalline polysiloxanes

Two series of monomers, 4-[4-(allyloxy)benzoyloxy]phenyl-3-(perfluoro-n-alkyl)ethyl propanoates and 2-(perfluoro-n-alkyl)ethyl-4-[4-(undec-10-en-1-oyloxy)-benzoyloxy] benzoates have been synthesised. These compounds contain a fluorinated chain obtained from 2-(perfluoro-n-alkyl)ethanol or from 2-(perfluoro-n-alkyl)ethyliodide, and an aliphatic chain containing a double bond attached to a mesogenic moiety. Their hydrosilylation with polymethylhydrogenosiloxane gives the corresponding polysiloxanes with a spacer with three or ten methylene units. These new fluorinated compounds are characterized by a combination of techniques consisting of differential scanning calorimetry (DSC) and thermal optical polarized microscopy. All the monomers exhibited smectogenic properties of type A but for the monomers with a long spacer between the unsaturated function and the mesogenic core (compounds B), the mesophase range decreases dramatically. All of the corresponding polysiloxanes exhibited a liquid crystalline behaviour over a wide temperature range. The influence of the fluorinated chain lengthening leads for the monomers and the polymers to an increasing of the transition temperatures. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4487–4496, 1999     

Periodic electro-optical characteristics of ion-doped Smectic A phase liquid crystals driven by a low-frequency electric field

Functional liquid crystal (LC)-based electro-optical materials are promising candidates in a wide range of smart fields due to their excellent external stimuli-responsive characteristics. Herein, ion-doped Smectic A (SmA)-phase LCs gradually change from a transparent to a scattering state and then return to the transparent state via a circularly driven low-frequency electric field. All optical states can be maintained after removing the electric field. This phenomenon is due to charge transport and convection effects that appear and disappear periodically in SmA LCs doped with suitable ionic liquids. Diverse periodic characteristics were observed upon applying electric fields with different waveforms (e.g. square, sawtooth, and sine). Furthermore, the optical contrast of the periodic feature was abated by increasing the frequency of the electric field. These ion-doped SmA LCs can be widely used in multi-stable optical devices, optical switches, and timers, etc.     

Tolane oligomers: Model thermotropic liquid crystals

The liquid crystalline phases of several rigid-rod, non-polar tolane oligomers are characterized by differential scanning calorimetry and transmitted polarized light microscopy. We determine that a stable nematic phase can be formed at ambient pressure if the molecular axial ratio (length-to-width ratio) is greater than 4.5. A smectic phase forms in addition to the nematic phase if the axial ratio exceeds 6.1. Symmetrical fluorination of the terminal phenyl groups reveals that the liquid crystalline phase behaviour of these rigid rods is highly sensitive to perturbations of the charge distribution along the molecules. Nematic tolane oligomers can exhibit high stregth disclinations (s = ±3/2 and ±2) in their schlieren textures, and we discuss conditions that promote the stability of these defects.     

Phase separation in mixtures of thermotropic liquid crystals and flexible polymers

The spinodal equation and the concentration-induced anisotropic-isotropic transition equation of the mixtures of thermotropic liquid crystals and flexible polymers have been studied by using the molecular field theory The calculations of the phase diagrams of this system show that,besides the isotropic classic spinodal curve,there ex ists an anisotropic spinodal curve which has not been reported in literature.These two spinodal curves can be linked up by the concentration-induced anisotropic-isotropic transition line.In the various phase regions,demixing may take place due to different phase separation mechanisms.The phase equilibrium curve cannot always join the.spinodal curve at a critical point.These results are considered very meaningful for the understanding of the special properties of liquid crystal/polymer composites and very useful for controlling the morphology and the performance of PDLC materials     

Synthesis of novel and regioselectively mesogen-incorporated thermotropic liquid crystals from cellulose derivatives

Regioselectively mesogen-incorporated cellulose derivatives, in which the hydroxy group at C-6 is displaced by a bulky and rigid mesogenic group such as {4-[(4-methoxyphenoxy)carbonyl]phenoxy}acetate or [(4′-cyanobiphenyl-4-yl)oxy]acetate, and the C-2 and C-3 groups are displaced by octanoyl or lauroyl groups, were synthesized. Thermogravimetric and differential scanning calorimetric analyses of the final products, along with polarized optical microscopic observations, revealed that the obtained cellulose derivatives have a thermotropic liquid-crystalline nature and transition from the mesomorphic to the isotropic phase over a wide range of temperatures. These derivatives could be considered to be main-chain liquid-crystalline cellulosic polymers.     

Enhanced thermal response of the SAd1 layer thickness in highly fluorinated thermotropic liquid crystals

X-ray studies of a homologous series of rod-shaped liquid crystal molecules with one tail perfluorinated and the other protonated, reveal large decreases in the smectic A layer spacing with increasing temperature. These materials form unique dimer phases in which the smectic layer spacing is dependent on the length of the perfluorinated tail and independent of the length of the protonated tail. The chain statistics of the perfluorinated tail significantly influence the thermal expansion coefficient since the length of the fluorinated tail defines the smectic layer spacing. Thermal expansion coefficients for the layer spacing observed here are negative and nearly an order of magnitude greater than for typical protonated rod-shaped thermotropic liquid crystals in the SA phase.