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A systematic study of a binary system composed of 4-n-pentyl 4′-cyanobiphenyl (5CB) and 4-n-pentyl phenyl 4-n′-hexyloxy benzoate (ME6O.5) mesogens showing an induced smectic A at different molar concentrations has been done. Heat capacity and optical birefringence measurements have been performed around the N-SmA phase transition region. The heat capacity peaks could be fitted well below the N-SmA transition by means of an extended Landau mean-field model. The first-order nature of the transition throughout the composition range can be inferred. This transition is rather close to the tricritical point when the nematic range is sufficiently increased. The latent heat decreases with the increase in the nematic range. For large nematic range, the latent heat drops to zero and the heat capacity peak associated with N-SmA phase transition disappear, contrary to previously reported most of the usual N-SmA phase transition. Precision birefringence measurements also agree well with the heat capacity data. [ABSTRACT FROM AUTHOR]

Using a thermodynamic model developed by us to study the structural and electro-optical properties of ${\rm Sm\; C}_{\rm A}^{\rm \ast }$ Sm C A ∗ phase, we investigate the temperature dependence of helical pitch, tilt angle and spontaneous polarization of a homologous series of fluorinated biphenyl benzoate esters (3FnHBM6, n = 2, 5, 7) and one of the series W-316-3 obtained from the mixture of two chiral liquid crystalline compounds 6F2OBi and 3F6HBM6. The free-energy density of the system exhibiting ${\rm Sm\; C}_{\rm A}^{\rm \ast }$ Sm C A ∗ phase is written as an expansion series in terms of all the relevant degrees of freedom: ${\bf Q}_{{\bf ij}}$ Q i j , ψ, P, q and the resulting coupling terms between these order parameters. The values of Landau coefficients are determined from the experimental data of antiferroelectric mesogens 3FnHBM6 (n = 2, 5, 7) and W-316-3 in the ${\rm Sm}\; {\rm C}_{\rm A}^{\rm \ast }$ Sm C A ∗ phase. Using these coefficients, the electro-optical and structural properties have been studied. We have found good agreements between the theoretical and experimental results. [ABSTRACT FROM AUTHOR]

A new four series of 2,2′-([1,1′- phenyl or biphenyl]-4,4′-diylbis(azanediyl)) bis(N′-((E)-1-(4-alkoxyphenyl) ethylidene) acetohydrazide) [V-XI]a,b and 1,1′-(2,2′-([1,1′- phenyl or biphenyl]-4,4′-diyl bis(azanediyl)) bis- (acetyl)) bis(3-(4-ethoxyphenyl)-1H-pyrazole-4-carbalde hyde) [XII-XVIII]a,b have been synthesized by varying terminal lateral alkoxy chain length (n = 1–3, 5–8), central linkage group (phenyl or biphenyl) and induced pyrazole heterocyclic ring in the main chain. The last two series were synthesized by the cyclization of substituted acetophenone hydrazones with Vilsmeier–Haack reagent (DMF/POCl3) to produce 4-formylpyrazole derivatives. The chemical structures of the synthesized compounds were examined by elemental analysis, FTIR and 1H-NMR. The results are in agreement with the considered molecular structure. The liquid crystalline behaviors were studied by using hot-stage optical polarizing microscopy (OPM) and differential scanning calorimetry (DSC). The correlation between the molecular structures and mesomorphic behavior and transition temperatures was discussed. [ABSTRACT FROM AUTHOR]

Pillar[5]arene (P5A) mesogens were synthesized by decorating the central P5A core with ten benzylether dendron via click reaction. Each benzylether dendron was terminated with multialkoxy chains. Such P5A mesogens can self-assemble into liquid crystal (LC) phases with layer structure (Smectic A phase) and tubular structure (Colhex/p6mm phase). Molecular packing models for these mesophases were initially established. Additionally, such P5A mesogens can act as chemo-sensor to recognize Fe3+ and Cu2+. The influence of the number of terminal alkoxy chain on the self-assembly and chemo-sensor properties of these P5A derivatives were investigated. [ABSTRACT FROM AUTHOR]

A distinct feature of the layer spacing has been observed on entering the SmC phase: the layer thickness initially decreases down about few degrees below the SmA to SmC transition temperature and then starts to increase again despite to the molecular tilt angle increases further with a reduction in temperature. This observation cannot be explained by the tilting of the molecule as an entity. Our results of the IR spectroscopy show that the orientational behaviours of terminal chains are distinctly different from that of the rigid core and clearly show that any model considering orientation of the molecule as an entity cannot be correct. A compensation model is used to explain it, where a contraction of the layer caused by the tilt of the mesogen is re-compensated by a simultaneous expansion of the layer of the fluorinated chain. [ABSTRACT FROM AUTHOR]

This paper presents the results of the study of four chiral mesogens with the acronym (4X1X2). The investigated compounds might be of interest for use as components of multicomponent mixtures useful in technical devices. The compounds have high chemical stability. Their mesomorphic properties were tested by means of polarizing optical microscopy and differential scanning calorimetry. The helical pitch of the prepared compounds and mixtures was estimated using the selective reflection method. Their phase smectic layer structure and usefulness for formulation of multicomponent antiferroelectric mixtures were then reported. [ABSTRACT FROM AUTHOR]

Microtextural polarization, phase transitions, and electro-optical effects are studied in a series of nanocomposites, grown by mixing alkyloxybenzoic acids (nOBAs), displaying hydrogen-bonded dimeric liquid crystal (LC) state, with non-mesogens (single-walled carbon nanotubes (SWCNTs), perfluorooctanoic acid) or mesogens (bent-core LC compound D14F3). Each of the studied nanocomposites, in which thenOBA serves as a matrix, forms complexes with bent-shaped dimeric, caused by the interaction between the dopant structural units and the dimer rings. This feature, coordinated with the surface anchoring, bulk and electrical effects, leads to drastic reduction of the LC system symmetry. As a result, transitions from achiral (characteristic for the pristinenOBA) to chiral states (including ferroelectric smectic C with C2symmetry and ferroelectric smectic CGwith the lowest C1triclinic one) take place. The functionalization of the SWCNTs causes drastic increase of the ferroelectricity. [ABSTRACT FROM AUTHOR]

The most important goal of our research is to show the influence of the ‘guest’ (bent-core mesogen, 1,3-phenyldicarboxylatebis{4-[(4-octylbenzoyl)sulphanyl]phenyl} [IFOS8], banana-shaped liquid crystal [BLC]) on the ‘host’ (calamitic liquid crystal [CLC], (S)-(+)-1-methylheptyloxybiphenyl-(4-n-octylphenyl)thiobenzoate [MHOBS8]), on the stability and the destabilization of the antiferroelectric B2 and the ferroelectric smectic C* (SmC*) phases, and change of the temperature ranges of other phases in the binary liquid crystal mixtures. This work is focused on polymorphism of three new binary liquid crystal mixtures, exhibiting a ‘guest–host’ (guest liquid crystal–host liquid crystal [GH-LC]) effect. MHOBS8 has, among others, a ferroelectric SmC* phase, and IFOS8 assumes the B2 phase with antiferroelectric properties. The observed properties of the mixtures, such as variation of the phase transition temperatures, spontaneous polarization, tilt angle and switching time, are characteristic of a ‘guest–host’ mixture. The influence of BLC on the character of the interactions within the CLC host is discussed, with particular attention paid to electro-optical properties of the GH-LC mixtures. [ABSTRACT FROM AUTHOR]

The phase behaviour and mesomorphism of poly(4-(6-propenoyloxyhexyloxy)benzoic acid) (PPOHBA) and 4-pentyloxybenzoic acid (POBA) is studied using variable-temperature Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. PPHOBA exhibits a smectic C phase and POBA, a nematic phase. The temperature dependence of the Fermi resonance bands associated with the hydroxyl groups and of the carbonyl stretching region in the FTIR spectra indicates that there is a dynamic equilibrium between monomers and open and closed dimers formed by hydrogen bonding between benzoic acid moieties. The nematic phase observed for POBA is linked to the anisotropic cyclic dimer, while an abrupt increase in the concentration of monomer drives isotropisation. In PPOHBA, hydrogen-bonded supramesogens promote smectic behaviour, while hydrogen-bonded crosslinks stabilise the lamellae. The increased viscosity arising from this dynamic crosslinking is offset by the flexibility of the acrylate backbone and alkyl spacers. [ABSTRACT FROM AUTHOR]

In order to study the influence of molecular structure peculiarities on supramolecular organization and properties in the bulk and thin films of discotic mesogens six new mix-substituted phthalocyanine derivatives with 3,6-dioctyloxyphthalonitrile and 3,4,5,6-tetrachlorophthalonitrile fragments were synthesized. Temperatures of phase transitions, types of mesophase and their dependence on molecule structure, chemical nature, position and ratio of different substituents as well as presence of holmium in the metal complexes were analyzed. The behavior of the studied molecules on the boundary between water and air was investigated and the peculiarity of supramolecular organization in floating layers as well as in thin films was determined. Quenching of luminescence in solutions of the studied compounds in the presence of fullerene C60was determined, thus giving prospects for application of these compounds as sensors for fullerene microquantities. [ABSTRACT FROM AUTHOR]

The liquid crystal monolayer was obtained on Si (100) wafer using a hydrosilylation reaction catalyzed by Pt compounds. The chemical modification of the surface of silicon wafer was characterized using the attenuated total reflection IR spectroscopy and X-ray photoelectron spectroscopy. The silicon surface texture was evaluated with atomic force spectroscopy and high-resolution scanning electron microscopy. [ABSTRACT FROM AUTHOR]

The temperature dependence of the layer spacing of a series of chiral bi-mesogen organosiloxane liquid-crystal materials is presented. The detailed measurements were taken at the ELETTRA radiation source in Trieste on thin specimens contained between glass coverslips. In the materials with 10 and 11 spacers between the siloxane and the mesogenic moiety, it is observed that the temperature dependence of the layer spacing is not monotonous. In the material with six spacers, there is an abrupt change of 0.01 nm in the layer spacing between 35 °C and 36 °C. In this temperature range, domains with both layer spacing coexist. This observation is in agreement with polarised light microscopy observations; however, detailed differential scanning calorimetry (DSC) measurements show no heat associated with this transition. [ABSTRACT FROM AUTHOR]

The thermodynamic model, developed by us previously (Singh S, Singh S. Application of thermodynamic model to study the ferroelectric properties ofnALandnHLhomologous series. Phase Transit. 2013;86:531–540), has been modified to investigate the phase transition properties of SmC* phase and SmA–SmC* phase transition. As usual, in this approach, the free energy density of a system is written as an expansion series in powers of order parameters (tensor orientational order, scalar smectic order ψ and polarization vector order) and the couplings between these order parameters. Sincegoverns the tilt vector ξ, no term is included in the free energy density involving only ξ. The coupled equations for these order parameters are obtained by the minimization of the free energy density with respect to respective order parameters. A detailed analysis of the relative contribution of each individual term of the expansion series and the values of spontaneous polarization (P0), tilt angle (θ0) and pitch (p) as a function of temperature for the two homologous seriesnAL(n= 9, 10, 12) andnHL(n= 9, 10, 12, 14, 16) of ferroic mesogens is presented. The influence of the alkyl chain length on the ferroelectric properties has been analysed and found to be substantial. A close agreement between theory and experiment for all the mesogens has been observed. [ABSTRACT FROM AUTHOR]

Two new mesogenic homologous series of Schiff's base ester with chloroethyl tail having the following general formula have been synthesized. The molecular structures of the synthesized compounds were characterized by the standard spectroscopic methods and elemental analysis. The mesomorphic behaviour of these new Schiff's base esters was mainly investigated with the help of optical polarizing microscope. For some representative compounds differential scanning calorimetric study was carried out to support the optical observation of transition temperatures and associated enthalpies. In series I, lower members are non-mesogenic, whereas higher members exhibit smectic mesophase. In series II, methoxy to n -hexyloxy derivatives exhibit nematic mesophase, while the smectic A phase commences from n -propyloxy derivative and persists up to the last member synthesized. The mesomorphic properties of these two series of compounds are compared with each other and with structurally related systems. [ABSTRACT FROM AUTHOR]