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Although the mesomorphic phase as an intermediate state has been introduced to understand polymer crystallization, the understanding of the mesomorphic phase is far from complete. Here, the effect of chain mobility on the mesophase structuring in melt-quenched poly(ʟ-lactide) (PLLA) treated in low-pressure CO2 at 1.6–2.0 MPa and 0 °C was investigated using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and atomic force microscopy (AFM). The IR and AFM results demonstrated that the final degree of order and the kinetics of structural evolution during the CO2-induced mesophase formation were critically dependent on the CO2 pressure. This was attributed to the distinct dynamics of conformational evolution (gg to gt conformer transition) due to the different CO2 pressures. The thermal behavior from the DSC results showed that CO2 pressure dominated both the scale and dynamics of the chain motion of PLLA. At a lower CO2 pressure of 1.6 MPa, smaller-scale segmental motion was not replaced by the larger-scale cooperative motion that occurred at a relatively higher CO2 pressure of 2 MPa, which was favorable for faster mesophase formation. Consequently, by inhibiting direct crystallization under limited mobility conditions, it was demonstrated that different chain mobility controlled by CO2 pressure and thus CO2 solubility impacted the dynamics of the mesophase formation of PLLA. The present results have implications for understanding the role of chain mobility in determining the intermediate structural phases in semicrystalline polymers. [ABSTRACT FROM AUTHOR]

New Janus-type compounds were synthesised with two different hemispheres structures and properties. The structures contain cyanobiphenyl units linked with 3,4,5-tribenzyloxybenzene or 3,4,5-tridecyloxybenzene units. Also, the influence of the 1,3,4-thiadiazole heterocycle was studied. The mesomorphic properties were studied by differential scanning calorimetry, polarised light optical microscopy and thermal gravimetric analysis. The mesophases obtained depend on the structure of the hemispheres, even obtaining mesophases different from the initial ones. The new materials synthesised presented photoluminescent properties, which were studied in solution. [ABSTRACT FROM AUTHOR]

A series of 2,3-difluorophenylene-based negative liquid crystals which own different terminal groups has been synthesised in high yields through many classical named reactions such as Suzuki coupling and Williamson etherification. Thermal properties of these mesogens were tested by differential scanning calorimetry and the effects of the terminal groups on the melting points of molecules were evaluated. Dielectric anisotropies of the synthesised molecules were then measured and found that relatively long alkyl substituents would decrease the Δε value when compared with the ethyl. For the compound with a polar substitute on the long molecular axis, the introduction of 2,2-difluoroethyl would increase the negative Δε when it was put into the opposite direction of the original polar group, making this strategy a new access for the improvement of negative Δε. DFT calculations were carried out to analyse the orientation of the dipole moment in molecules and found that the introduction of 2,2-difluoroethyl had changed the orientation of the dipole moment into nearly perpendicular to the long molecular axis, which benefited the growth of the negative Δε value, revealing the mechanism of this strategy from the view of molecular level to some extent. [ABSTRACT FROM AUTHOR]

Structurally simple two rod-like mesogens with a three-ring core consisting of biphenyl and phenyl rings are synthesised to investigate the mesophase properties, molecular organisation and the orientational order parameter. In mesogen-1, a dodecyloxy terminal chain is present on the biphenyl ring while the phenyl ring is free from substituent. For mesogen-2, in addition to the dodecyloxy chain, the butyl chain is placed on the phenyl ring. The Hot-stage optical polarising microscopy (HOPM) and differential scanning calorimetry (DSC) measurements show smectic A (SmA), smectic B (SmB), and crystal E (CryE) phases for mesogen-1 and SmA, smectic C (SmC) and smectic F (SmF) phases for mesogen-2. The presence of smectic mesophases is established by X-ray Diffraction (XRD). 1D and 2D 13C solid-state NMR experiments are performed in smectic mesophases to find the orientational order parameters of the phenyl rings of the core. The main order parameter (Szz) of the mesogens in the SmB and SmF phase is in the range of 0.87–0.93. The excellent spectral resolution noticed in 13C NMR spectra in the SmB mesophase (mesogen-1) indicates that the internal rotations of the molecules along the long axis are primarily unhindered. [ABSTRACT FROM AUTHOR]

Two series of C2-substituted dimers carrying a central C2-hexyl- or C2-nonafluorohexyl malonate and two cyanobiphenyls attached via alkoxy spacers of various lengths (n = 6–12) were synthesised, and the mesomorphic properties were studied by differential scanning calorimetry, polarising optical microscopyand X-ray diffraction (wide-angle and small-angle X-ray scattering). The C2-substituent dimers together with the spacer lengths had a pronounced influence on the phase behaviour. In case of C2-hexyl-substituted dimers, shorter spacers favoured N phases (n = 6–9), while longer spacers favoured SmA phases (n ≥ 9). In addition, decreased clearing temperatures were observed. In contrast, C2-nonafluorohexyl-substituted dimers suppressed N phases and displayed only SmA phases. Moreover, clearing temperatures and phase stabilities considerably increased. Based on the experimentally determined layer thickness, a packing model for the SmA phases was proposed, where C2-substituted dimers displaced mesophases with molecules in a Y-conformation. As a result, less stable mesophases for C2-hexyl-substituted dimers due to weakened intermolecular interactions and more stable mesophases for C2-nonafluorohexyl-substituted dimers due to the fluorophobic effect and nanosegregation were obtained. [ABSTRACT FROM AUTHOR]

Two series of ten ester derivatives with four aromatic rings linked together by three different linkages (azo/ester/imine), 4‐((4‐substituted)diazenyl)phenyl 4‐((4‐alkoxybenzylidene)amino)benzoate (IVn X=OCH3 and Vn X=Br) were synthesized. These derivatives have an alkoxy chain in the para position of the phenyl ring with different lengths (n=3, 4, 6, 7, and 12) on one terminal side while the other side was substituted by methoxy and bromo groups linked to the p‐position of phenyl. The structures of all synthesized derivatives were proven by nuclear magnetic resonance (1H‐NMR, 13C‐NMR), elemental analysis (C,H,N), and Fourier‐transform infrared spectroscopy (FT‐IR). The Mesophase textures of the final esters were observed by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Only the nematic texture was observed in the methoxy derivatives while nematic and smectic A textures were shown in the bromo mesogens. All the homologous showed mesogenic behavior with wide thermal stability. From the results, it was found that the liquid crystalline behaviors of these derivatives are dependent on the substituted group (‐X) and the length of the alkoxy chain. The mesogenic behavior of these compounds was compared with other mesogens that have similar structures. [ABSTRACT FROM AUTHOR]

A new series of eight asymmetric homologues was designed and synthesised by the reaction of aroyloxybenzaldehydes with Wittig salt of methyl bromoacetate, where the length of the alkoxy chain was varied. All the compounds were found thermally stable up to 220°C. Differential scanning calorimetry, polarising optical microscopy and X-ray diffraction were used to study the mesomorphic properties, where a mesophase range of up to 80°C was obtained. The two shorter homologues with C3–C4 were nematic, the intermediate lengths were nematic and smectic A (SmA) with a progressive increase of the SmA domains and the longest homologue with C12 was purely SmA. The translational order parameter of the SmA mesophases showed that the molecular order inside the smectic layers increases with molecular length, associated with the higher stabilisation and predominance of the SmA phase. All compounds dispersed in solution absorb light in the ultraviolet region. [ABSTRACT FROM AUTHOR]

In this paper a synthesis, liquid crystal behaviours, photoluminescence and thermal conductivity have been described for new sets of unsymmetrical dimeric molecules with coumarin unit at one end connected to chalcones alky substitution by diether. Chemical proposed structure was confirmed by routine analytical methods using FT-IR, 1D NMR and 2D NMR spectroscopy and CHN elemental analysistechniques. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry and polarising optical microscopy with heating assembly. Most of the compounds are showing nematic mesophases with moderate transition ranges. Photoluminescence of compounds was examined and the results indicated that the emission in the blue region reveals that material has blue light emission properties. Moreover, thermal conductivity of the prepared compounds was measured, result indicated that slight change in the structure increased the thermal conductivity. [ABSTRACT FROM AUTHOR]

We report the synthesis, characterization and properties of a series of coordination polymers (CP) in which paddle‐wheel diruthenium (II,II) tetracarboxylate units are linked by tetrazine as axial ligand, a combination aimed to promote electron delocalization along the CP axis. The use of bulky equatorial 3,4,5‐tri(alkoxy)benzoates (B3OCn, n=10, 14, 18) warranted the columnar liquid crystalline nature of the targeted Ru2(B3OCn)4tz CP, which allowed their processing as extruded fibers. The liquid crystalline phases of both the polymers and their Ru2(B3OCn)4 precursors have been studied by means of polarized optical microscopy, differential scanning calorimetry, X‐ray diffraction and small and wide angle X‐ray scattering. We suggest herein some models for the supramolecular organization in the hexagonal and rectangular columnar mesophases these CP exhibited. Extrusion form the CLC phase lead to fibers in which the columnar axes were colinear with the fiber axis at a macroscopic scale. Electrical conductivity measurements on these fibers revealed high values (0.4 S/m) for the targeted CP. [ABSTRACT FROM AUTHOR]

New mesomorphic homologue series of laterally fluorinated azo/esters, 2-fluoro-4-((4-alkoxy)phenyl)diazenyl)phenyl 4-(alkoxy)benzoate (In/m), were synthesized and investigated their behaviour via experimental and computational tools. The prepared series bearing eight derivatives that differ from each other by the terminally attached alkoxy chain groups at their ends. Elemental analyses, FT-IR and NMR spectroscopy were carried out to elucidate their molecular structures. Mesophase and optical examinations of the synthesized homologues are conducted using differential scanning calorimetry (DSC) and polarised optical microscopy (POM). Mesomorphic characterisations revealed that all the laterally F substituted derivatives are monomorphic exhibiting nematic (N) mesophase with enantiotropic properties, except the longest terminal chain member possesses N phase monotropically. The comparative studies between the present group, I6/m, and the laterally-neat series revealed that the type and stability of the produced phase are dependent upon the influenced molecular dipole moment of the mesogenic core which is mainly dependent on the insertion of the lateral F atom. Computational approaches were carried by DFT calculations and the optimised structures of present investigated series have been deduced. DFT results revealed that, the incorporation of lateral F atom has essential effects on the stability of possible geometries as well as their thermal and physical parameters. [ABSTRACT FROM AUTHOR]

A new series of polysiloxane glassy cholesteric liquid crystal copolymers with menthyl- and cholesteryl-based mesogenic units in the side chains, denoted as P-MtxChy (x, y expresses the molar ratio of monomers Mt and Ch in copolymeric synthesis, and x + y = 7.) were successfully synthesised by hydrosilylation reaction. The mesomorphic properties and phase behaviours were studied by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction. Optical properties were investigated by the UV-VIS spectrum. Using the volume-excluding action of mesogenic units in side chains, we obtained glassy cholesteric liquid crystal copolymers. By varying molar ratio of Mt and Ch in copolymers, the helical pitch was adjusted into visible light region. With the increase of Mt, the maximum reflection wavelength off normal 8 ° shifted from 548 nm of P-Mt3Ch4 to 650 nm of P-Mt4Ch3 to 872 nm of P-Mt5Ch2, and the reflected colours changed from green to red. These well-oriented glassy films have shown good morphological stability below the glass-transition temperature (Tg) for more than a year. [ABSTRACT FROM AUTHOR]

Herein, we aim to investigate the influence of the cooling rate from the melt on stereocomplex formation of equimolar blends of enantiomeric star-shaped poly(lactide)s with a dipyridamole core. As evidenced by differential scanning calorimetry, wide-angle X-ray scattering and Fourier-transform infrared spectroscopy, melt cooling of equimolar blends of star-shaped poly(L -lactide) (SSPLLA) and star-shaped poly(D -lactide) (SSPDLA) resulted in the non-crystalline state. A careful analysis of WAXS and FTIR data revealed that the slow-cooled sample (10 °C min−1) exhibited the amorphous phase and the fast-cooled sample (50 °C min−1) resulted in the mesophase. On subsequent heating, the slow-cooled sample remained in the amorphous phase, whereas the fast-cooled sample crystallized (cold crystallization) exclusively into the stereocomplex at ∼90 °C. Aging of the slow-cooled sample at room temperature and subsequent heating led to the formation of the stereocomplex. Photoluminescence studies revealed that the cooling rate from the melt has a strong influence on core molecule (dipyridamole) aggregation and determines the geometry of interactions between the branches of SSPLLA and SSPDLA. In the slow-cooled sample, because of the longer residence time above the glass transition temperature, dipyridamole molecules form aggregated structures, whereas in the fast-cooled sample, dipyridamole molecules are distributed within the polymer matrix without much aggregation. Based on these results, we propose antiparallel chain packing in fast-cooled SSPLLA/SSPDLA blends because of the non-aggregation of dipyridamole core molecules and this geometry favored the exclusive formation of stereocomplex. On the other hand, due to the possible aggregation of dipyridamole molecules, the slow-cooled sample led to topological and geometric constraints where the interactions between SSPLLA and SSPDLA chains prevented the crystallization. The present findings could open new avenues for the design of a variety of macromolecular architectures for a better understanding of the stereocomplex formation mechanism of chiral polymers. [ABSTRACT FROM AUTHOR]

Three sets of new rod-shaped liquid crystals with one terminal fixed branched alkyl chain, other terminal with varying normal alkyl chain, and central naphthalene with terminal branched chain derived symmetric molecules were synthesized and characterized. Chemical structures were confirmed by standard analytical methods. Liquid crystal properties were evaluated with the help of differential scanning calorimetry, polarized optical microscopy and X-ray studies. All the compounds favoured to exhibit highly birefringent smectic and nematic mesophase textures. Further, symmetric naphthalene derivatives preferably exhibited nematic mesophase with elevated transition temperatures. [ABSTRACT FROM AUTHOR]

A novel series of calamitic, complementary hydrogen-bonded (HB), meta-extended Schiff base core containing liquid crystalline (LC) complexes with ethoxy chain at one end and varied flexible chain at other end, viz., (4)EoBD(3)AmBA:nOBAs for n = 3–12 is reported. 1H, 13C NMR and FTIR spectroscopy confirm complex formation. LC phases, phase transition temperatures (TC) and enthalpy are characterized by polarizing optical microscopy and differential scanning calorimetry(DSC). SmA, SmC, SmBcryst,SmF, SmI, SmE, SmG and SmH phases are exhibited. Clearing and melting temperatures exhibit odd–even effect. Schiff base bridged by oxygen atom promoted of smectic phase occurrence. Complementary HB-induced and -enhanced tilted smectic phase range. Large LC phase variants, i.e., tetra, penta and hexa are observed. Hexa LC phase variant for n = 6 and 12. Unlike in p-n-alkoxy benzoic acids (nOBAs), Nematic phase is quenched. Quasi two-dimensional LC SmF and SmI phases identified. Lower (for n = 3,5), intermediate (for n = 6,7) and higher (n = 9) homologues exhibit 3D SmBcryst phase. Monotropic LC phase occurrence is also noticed. Apart from other LC phase transitions, SmA–SmC transition is mostly found to be second order or very weakly first order nature. Phase diagram by DSC infers existence of multi-critical points in the vicinity of SmF and SmI phase structures with psuedo hexagonal packing. Influence of meta-extended core, complementary HB and flexibility component are discussed for LC phase abundance. Role of orientational disorder induced by flexible component discussed. In comparison with LC phase occurrence in (4)MeoBD(3)AmBA:nOBAs, shielded inductomeric effect is argued for large thermal range of tilted smectic phases. Integrated and differential heat energies are estimated in successive heating and cooling scans to investigate optimized realization of LC phases. Results are discussed in the wake of contemporary reports in other LCs. [ABSTRACT FROM AUTHOR]

C3‐symmetrical, alkoxyphenyl substituted 2,5,8‐(tris‐1,3,4‐oxadiazol‐2‐yl)benzo [1,2‐b; 3,4‐b′; 5,6‐b′′]trithiophenes (OXD‐BTT) are synthesized via threefold Huisgen‐reaction. A broad variation of alkoxy substitution pattern and chain lengths is reported. The thermal behavior was investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM) and thermogravimetry (TGA). Optical properties were studied via UV‐Vis and fluorescence spectroscopy. Structural information of the LC phases was gained from X‐ray diffraction on oriented fibers. OXD‐BTT provide enormous phase widths (ΔT≥289 K) with clearing points close to thermal decomposition. Most of the derivatives exhibit two different mesophases, the lower phase with a rectangular 3D‐structure and a hexagonal 2D‐lattice at higher temperature. The variation of the chain length allows a tuning of melting and clearing points. OXD‐BTT emit blue light with fluorescence quantum yields up to 30 % in good solvents. The emission is very sensitive to aggregation, thus, in poor solvents the emission intensity decreases, and red shift of maxima occurs. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis of novel liquid crystals (LCs) based on 5-membered pyrazoline heterocycle. The synthesis of pyrazoline derivative was carried out by [3 + 2] 1,3-dipolar cycloaddition reaction of benzaldehyde phenyl hydrazone (1) with acrylonitrile, mediated by chloramine-T as the oxidising agent, followed by addition of hydroxylamine hydrochloride, and subsequently alkylated with various alkyl chains to afforded the title compounds. The LCs properties were investigated using differential scanning calorimetry and polarising optical microscopy. For title compounds with longer alkyl chains, monotropic columnar hexagonal mesophase was characterised by XRD analysis. The mesophase-formation was driven by intermolecular hydrogen bonds despite their non-discoid molecular structure. [ABSTRACT FROM AUTHOR]

A new family of supramolecular liquid crystalline compounds with a calix[4]arene core and two linking groups appended on four sides, exhibiting a wide range of hexagonal columnar phases, has been synthesised and well characterised. The liquid crystal behaviour of the novel materials was studied by using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and was further confirmed using high-temperature powder X-ray diffraction (XRD). An electrochemical study was carried out using cyclic voltammetry (CV) and the results were compared with theoretical values obtained from a DFT study. These compounds showed light sky-blue luminescence in solution and as a thin film under long-wavelength UV light. It was observed that all the prepared target compounds exhibited enantiotropic mesophases with good thermal stability. The structural and conformational characterisation of these new compounds was achieved using various spectroscopic techniques, including FT-IR, 1H NMR, 13C NMR and MALDI-TOF. The relationship between the structure and the mesomorphic behaviour of the compounds containing an ethyl bridge with linked ester groups (5a–5d) is discussed. This new class of supramolecular derivatives is promising, especially considering the emissive nature and stabilisation of their columnar hexagonal mesophases, and their high range of thermal stability. [ABSTRACT FROM AUTHOR]

A new homologous series of imine‐ester compounds ({(1E)‐[5‐(4‐nitrophenyl)‐2‐thienyl]methylene}amino)phenyl‐4‐alkoxybenzoate (series IIIa‐k) comprising thiophene ring as a rigid core has been synthesized. The molecular structures of these esters were proven by means of Fourier‐transform infrared spectroscopy (FT‐IR), nuclear magnetic resonance (1H‐NMR, 13C‐NMR) and mass spectrometry (MS). Different liquid‐crystalline textures (nematic and smectic A) have been observed by optical polarizing microscopy (OPM) and differential scanning calorimetry (DSC) techniques. The first four homologues in this series (IIIa‐IIId) displayed a nematic phase while the most of homologues that have longer alkyl group exhibited both nematic and smectic phases. The liquid crystalline phases of these compounds are dependent on the length of alkyl chain of the molecules. The mesomorphic phase stability of the prepared compounds in the presence of thiophene ring within chemical structures of the mesogens has been discussed comprehensively, and the liquid crystalline behaviors of these compounds have been compared with other reported mesogens that have similar chemical structures. [ABSTRACT FROM AUTHOR]

New series of the Schiff base/esters, 4-((2′-or 3′-fluorophenylimino)methyl)phenyl-4″-alkoxy benzoates were prepared and their mesophase behaviour investigated. The type of the mesophase and its transition temperature were determined by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The optimised structures of Schiff base/ester and their azo/ester groups have been deduced theoretically by density functional theory (DFT). Each group of homologues differs from the other by the position of the fluorine atom on the terminal benzene ring, in addition to laterally neat homologues. Comparative studies revealed that the position and orientation of the lateral fluorine atom as well as the type of the linking core not only affects the melting temperature but also the mesophase stability. DFT results showed that the type and stability of the mesophase could be illustrated in the terms of calculated dipole moment, polarisability, thermal energy and molecular electrostatic potential. [ABSTRACT FROM AUTHOR]

Two homologous series of the three-ring 4ʹ-(4"-alkoxy-2"-(or 3")fluoro phenylazo) benzoates terminated with 2-(or 1-) naphthyl groups (Ind&e or IInd&e), respectively, were prepared and their mesophase behaviour investigated via differential scanning calorimetry, whereas the type of the mesophase identified by polarised light microscopy. Molecular structures of compounds prepared were first characterised via infrared, 1H-NMR and elemental analyses. Transition temperatures were correlated with the alkoxy chain length (n) that varies between 6, 8, 10, 12, 14 and 16 carbons. Comparative studies were made to investigate the effect of including the lateral fluorine atom, and its orientation, into the previously investigated fluorine-free analogues, namely, 2-(or 1-) naphthyl 4ʹ-(4"-alkoxyphenylazo) benzoates (Ina and IIna). The study was extended to investigate the effect of replacing the methyl group in the previously prepared 2"- and 3"-methyl analogues (Inb&c or IInb&c) with the fluorine atoms on their mesophase behaviour. [ABSTRACT FROM AUTHOR]

Two homologous series of the three-ring azo/ester compounds 2-(or1-) naphthyl 4ʹ-(4ʹ'-alkoxy phenylazo) benzoates (Inaand IIna) were synthesised. A lateral methyl group was introduced in different positions of the alkoxy phenyl moiety, in position-2 to give series Inb and IInb and in position-3 to give series Inc and IInc. Molecular structures were characterised via elemental analyses, infrared and 1H-NMR. Their mesophase characteristics were investigated by differential scanning calorimetry (DSC) and their phases identified via polarised light microscopy (PLM). Transition temperatures were correlated with the alkoxy-chain length (n) that varies between 6, 8, 10, 12, 14, and 16 carbons. Comparative studies were first made to investigate the effect of including the extra fused benzene ring, and its orientation, into the previously investigated three-ring compounds, 4-phenyl 4ʹ-(4′′-alkoxyphenylazo) benzoates (IIIna). Investigation of the mesophase behaviour was extended to cover the effect of introducing the lateral methyl group and its position. The comparison between the present six series and their corresponding phenyl analogues IIIna,b,c, indicated that the 2-naphthyl analogues, Ina,b,c, exhibit the highest mesophase stability. Whereas, the steric effect of the protruded naphthalene group destabilises all mesophases and appear only monotropically. The results were discussed in terms of polarisability effect. [ABSTRACT FROM AUTHOR]

A series ofnovel N1-(6-((4-(alkyloxy)benzylidene)amino)pyridin-2-yl)-N4-(6-((E)-(4- (alkyloxy)benzylidene)amino)pyridin-2-yl)terephthalamidewere prepared from N1,N4-bis(6-aminopyridin-2- yl)terephthalamideand 4-alkoxy benzaldehydesby thermal condensation reaction in absolute ethanol at reflux condition. The structure of the target compounds were elucidated by FT-IR spectral data and determining the elementscontent(C.H.N%). The liquid crystal properties of these products were studied by measuring the values of the phase transition temperatures by differential scanning calorimetry (DSC) and the texture of mesophases by using optical polarizing microscopy (POM).The target compounds showed significant liquid crystal properties. [ABSTRACT FROM AUTHOR]

The mesomorphic isotactic polypropylene was prepared by rapid compression instead of the common method of temperature quenching, and their phase transition under high pressure was investigated in depth by combining wide‐angle X‐ray diffraction, small‐angle X‐ray scattering, and differential scanning calorimetry techniques. It was found that annealing under pressure can promote the further arrangement of chain segments of the mesophase toward the crossed state in the orthorhombic γ‐phase, and the long period of the mesophase slightly decreased from 8.2 to 7.2 nm. The kinetics of this meso‐γ transition strongly depends on pressure. As annealing pressure increased, the mobility of molecular segments was reduced, and then the onset and finishing time of phase transition were both delayed significantly. A critical annealing pressure was found between 1.6 and 1.75 GPa, which determines whether the phase transition occurs or not. When pressure reaches 1.75 GPa, mesophase did not transform at all within 120 min. Based on the results, a reasonable mechanism was proposed to show the crystallization process of mesophase under high‐pressure annealing. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 651–661 [ABSTRACT FROM AUTHOR]

A series of new calamitic liquid crystals, 2-[4-(4-alkoxybenzoyloxy)benzylidenamino]benzothiazoles comprising a heterocyclic (benzothiazole) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were prepared and characterized. This series comprises eight members wherein the members vary by the length of alkoxy chain (CnH2n+1O-, where n = 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in conformity with the expected structure. Their thermotropic behaviors were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first member of the series (n = 4). As the alkoxy chain increased to n = 6, 8, 10, 12, 14, the nematic phase appeared together with an additional SmA phase. When moving from n = 16 until the highest member (n = 18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA). [ABSTRACT FROM AUTHOR]

Abstract The synthesis of a series of symmetrical liquid crystals having naphthalene as the central rigid core and attached to long chain flexible 4′-alkoxybenzoate moiety at positions 2,6 - of the aromatic ring are reported. The mesophase behavior of the molecules was investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction studies. The studies reveal that the synthesized compounds exhibit stable enantiotropic mesophase of Smectic A (SmA) and Nematic (N) phase. The mesophase appearance is independent of the length of the alkyl chain. The molecular structure was determined by single crystal X-ray diffraction technique. The derivative with n- heptyloxy- flexible chain crystallizes under triclinic, P 1 ¯ space group with unit cell dimension a = 5.569(3) Å, b = 10.540(5) Å, c = 15.254(9) Å, α = 73.434(18)o, β = 80.807(19)o and γ = 82.02(2)o, V = 843.1(8) Å3. The dihedral angle between the naphthalene ring system and the benzoate moiety is 63.63(2)o. Graphical abstract Image Highlights • We have synthesized symmetric naphthalene centered molecules. • All the molecules were characterized by UV, IR, NMR analysis. • Liquid crystal property was evaluated by DSC and POM techniques. • Single crystal structure was confirmed by X-ray analysis. [ABSTRACT FROM AUTHOR]

The synthesis and material properties of a series of new liquid crystalline compounds containing thioether and cholesteryl, these homologues with different alkyl chain lengths of 2-8, are reported. Thermal analysis shows that all oligomers have wide mesophase temperature ranges with high thermal stability. The oligomers were determined by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). The molecule not only successfully exhibits strong optical properties and rainbow colours, but also the cholesteric helical pitch decreased with increasing temperature. The mesogenic incidence and tendency were found to be strongly dependent on the numbers of carbon in the flexible alkyl chain. Even members formed widely mesophase compared to odd members that showed narrower ones. The reflection wavelengths of 6S8Ch are almost across the entire visible region when they are heated, which offer tremendous potential for various optical applications. Also, it not only shows a lower transition temperature but also has a narrower cholesteric phase compared to analogues with alkoxy groups. These results not only provide practical design principles for the synthesis of new sulphur-containing LC materials with optical applications, also make a significant contribution to use as thermally sensitive liquid crystal devices requiring fast response. [ABSTRACT FROM AUTHOR]

Five groups of 4-substituted phenyl 4ʹ-(2ʺ- (or 3″-) substituted-4ʺ-alkoxyphenylazo) benzoates (Ina-c to Vna-c) were investigated in which, within each group, the length of the terminal alkoxy group varies between 8 and 16 carbons, while the other terminal substituent, X, is a polar group that alternatively changed between the electron-donating CH3O and the electron-withdrawing Br group, in addition to the un-substituted analogue (X = H). The lateral substituent (Y) in the five groups I-V varies, respectively, between H, 3-CH3, 2-CH3, 3-F and 2-F. Their mesophase stabilities were determined by differential scanning calorimetry and phases identified by polarised light microscopy. The two newly prepared groups of compounds (IVna-c and Vna-c) are structurally characterised by infrared, 1H-NMR, mass spectroscopy, thermogravimetric and elemental analyses. Binary phase diagrams were constructed for each pair of isomers from groups IV and V bearing the same wing substituents but the lateral F is attached to different positions (2ʺ or 3″). [ABSTRACT FROM AUTHOR]

In this research was studied the behavior of a polyurethane material synthesized by the partial replacement of PEG-400 for molasses at different compositions. It was observed in the IR spectra of the different samples the absence of the peak at 2268 cm -1 characteristic of the group -NCO which allowed to deduce that the reaction proceeded satisfactorily between the diisocyanate and the different polyols, the characterization was performed using differential scanning calorimetry, electrical impedance and optical microscopy. In the DSC heating scans the endotherms corresponding to the glass transition temperature, Tg, with values of: 74, 64, 55 y 74 °C, For substitution percentages of 10, 20, 30 y 40% w/w respectively. For the same polyurethanes, the melting temperature, Tm, with values of: 153, 164, 175 y 179 °C. The shift experienced by Tg and Tm has been associated with increased hard segments in the matrix as a result of the carbohydrates addition to the polymer chain. The impedance was measured in the range of 10 to 500,000 Hz at room temperature, finding significant variations in conductance depending on the composition of molasses, which is related with the energy gap between HOMO and LUMO, in addition to a significant shift in the point of dielectric relaxation. Optical microscopy revealed significant changes in morphology and size of the pores with average values approximate: 40, 53, 94 and 102.24 µm respectively, and a value of 134 µm for reference material. These variations in pore size have been attributed to the variation of reaction rate due to the decrease of the content of PEG-400 in the array. [ABSTRACT FROM AUTHOR]

A small series of dendrimers consisting of a star-shaped triphenylbenzene core unit and bulky lateral groups was synthesised and their mesomorphic properties were investigated via differential scanning calorimetry, polarising optical microscopy and small- and wide-angle X-ray scattering (WAXS). The dendrimers showed two enantiotropic hexagonal columnar mesophases. The combination of temperature-dependent and fibre-extruded WAXS revealed a helical arrangement in the low-temperature and a zig-zag orientation in the high-temperature mesophase. Furthermore, at the mesophase-to-mesophase transition, the intracolumnar reorganisation and the intercolumnar lattice extension occurred at different time scales, with the latter process being the slower one. [ABSTRACT FROM AUTHOR]

• Twenty-eight nematogenic homologues were prepared, having longer molecular axis. • All derivatives were found to be enantiotropically nematic. • Geometry of all mesogenic compounds were optimized with DFT method. • Longer molecular axis and π-π interaction were used to investigate interaction between the molecules. In this article, we have synthesized twenty-eight nematogenic homologous derivatives of allylidene base with cinnamates and benzoates linkages. All nematogenic homologous derivatives were characterized by ultraviolet spectroscopy, Infrared and proton magnetic resonance with study of their mesophase properties by the polarized optical microscope (POM) where they were found to be enantiotropically nematogenic. The thermograms of mesophase transition enthalpies and entropies were recorded by differential scanning calorimetry (DSC). The geometries of all molecules were optimized by DFT/B3LYP method using a basis set def2-SVP, the result of these calculated molecule's geometries for all molecules showed to have an electron-rich longer molecular axis, which enables the molecule to form a stronger pi interaction with adjacent molecules and induces the nematogenic mesophase behavior. The effect of an additional diene system on mesophase behavior of a stepped type of molecules was also studied. The role of the number of rings on mesophase behavior as an odd-even effect on mesophase transition temperature as well as the role of the substitution on the terminal ring for the same was considered. [Display omitted] [ABSTRACT FROM AUTHOR]

Numerous reports have shown that the self-assembling properties of 12-s-12 bis(quaternary ammonium) gemini surfactants in aqueous solution are significantly influenced by s, the number of methylene groups in the covalent spacer. However, the role played by s on the phase behavior of the single compounds has not been investigated in a similarly systematic way. Here, we report on the thermotropic phase behavior of the anhydrous compounds with s = 2-6, 8, 10, and 12, resorting to differential scanning calorimetry (DSC), polarized light microscopy (PLM), and X-ray diffraction (XRD). All of the compounds show a stepwise melting behavior, decomposing at 200 °C. As the spacer length increases, nonmonotonic trends are observed for the thermodynamic parameters of the thermotropic phase transitions, mesophase formation, and solid-state d00l spacings. In particular, the number and type of mesophases (ordered smectic phases and/or fluid smectic liquid crystals) depend critically on s. Further, upon heating molecules with s < 8 decompose before the liquid phase, while those with long spacers, s = 8-12, reach the isotropization (clearing) temperature, hence forming both ionic liquid crystals and ionic liquid phases. We demonstrate that the melting behavior and type of ionic mesophases formed by gemini molecules can be usefully manipulated by a simple structural parameter like the length of the covalent linker. [ABSTRACT FROM AUTHOR]

A comparative study of our established synthetic approaches to hexasubsituted triphenylenes 2,3-dicarboxylic esters containing four identical β-alkoxy and two adjacent β-alkoxycarbonyl side chains shows that the phase behaviours of small-sized discotic liquid crystals can be tailored over a wide range by simply varying the length of the peripheral alkyl chains. All the prepared esters in two series were observed to form a single hexagonal columnar phase, except forTp4-1having four β-butyloxy and two adjacent β-methoxycarbonyl chains which displays two columnar mesophase behaviours with a transition from the columnar plastic phase to hexagonal columnar phase. A significant difference between the two mesophase was observed in the variable temperature X-ray diffraction studies, and the mesophase assignment was also confirmed by polarising optical microscopy and differential scanning calorimetry. Moreover, the prepared esters in each series display the general trend of decreasing clearing temperature upon increasing alkoxy or alkoxycarbonyl chains length. The intermediate triphenylene 2,3-dicarboxylic acids were also found not only to exhibit columnar hexagonal mesophase over a narrower temperature range by maintaining high melting and clearing points but also to form organogel on mixing with toluene or dichloromethane with the assistance of hydrogen bonding. [ABSTRACT FROM PUBLISHER]

Series of laterally monofluorinated compounds, 2-(4ʹ-alkoxy-3-fluorobiphenyl-4-yl)-1H-benzimidazole derivatives (nPPF(3)Mx) bearing different substituents (H, CH3, NO2, coded as nPPF(3)MH, nPPF(3)MM and nPPF(3)MN, respectively) at 5-position, were prepared and their structures were characterised. According to the results from differential scanning calorimetry and polarising optical microscopy, the present compounds nPPF(3)Mx exhibit enantiotropic smectic mesophases, for which the mesophase ranges are 13–67 and 47–111°C on heating and cooling for nPPF(3)MH, 84–112 and 126–154°C for nPPF(3)MM, and 23–102 and 49–117°C for nPPF(3)MN, respectively. Compared to non-fluorinated analogues, monofluorinated nPPF(3)Mx have low melting/clearing points and display enhanced mesophase range both in heating and cooling, which are attributed to the disruption of the side-to-side intermolecular packing caused by theortholateral fluoro substituents and the increased dipole–dipole interaction between the polar fluoro-substituted molecules, respectively. It is noted that nPPF(3)MM and nPPF(3)MN show a much wider mesophase range than nPPF(3)MH, which suggest that the substituent at benzimidazole moiety can improve the mesophase stability. [ABSTRACT FROM PUBLISHER]

Properties of 4-n-pentylphenyl-4'-n-octyloxythiobenzoate (8OS5), belonging to the nOS5 homologous series, have been studied by complementary methods. The phase sequence, the phase transition temperatures, the thickness of molecular layers, the average distance between long axes of molecules and the correlation length were determined during cooling and heating. For the first time, simultaneous X-ray diffraction and differential scanning calorimetry measurements have been used to study mesomorphic properties. The results are compared with the ones obtained in standard measurements by means of differential scanning calorimetry, X-ray diffraction and polarizing optical microscopy. Meaning of experimental procedures applied in investigations of monotropic mesophases below a melting point is discussed. [ABSTRACT FROM AUTHOR]

In this study, the synthesis, structural characterization and mesomorphic properties of newly thirteen calamitic rod-shaped compounds derived from chalcone and 4-n-alkoxy benzoic acid. Here we present, chalcone as central group and terminal side substituted iodo (−I) group containing homologous series. Comp.C1displayed nonmesogenic nature, while comp.C3to comp.C18shows enantiotropic smectic plus nematic property except comp.C2which show only nematic phase. It is shown that chalcone as central linking unit favors a calamitic liquid crystalline behaviour in molecules. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC). Thermal stabilities for smectic and nematic mesophases are 150.18 and 163.58 respectively. [ABSTRACT FROM PUBLISHER]

Eighteen binary mixtures are prepared from three thermotropic double hydrogen bonded liquid crystal complexes formed by Mesaconic Acid (ME) and various alkyloxy benzoic acids, namely ME + 5BAO, ME + 11BAO and ME + 12BAO where 5BAO, 11BAO and 12BAO represents pentyloxy benzoic acid, undecyloxy benzoic acid and dodecyloxy benzoic acid respectively. Two sets of binary mixtures (ME + 12BAO with ME + 5BAO and ME + 11BAO with ME + 5BAO) are formed by varying their molar ratio in steps of 0.1 to 0.9 which leads to the formation of eighteen binary mixture complexes. Existence of different energy bands in the binary mixtures is identified from the analysis of Fourier Transform Infrared Spectroscopy (FTIR). Phases such as nematic and smectic C are observed in all the binary mixtures which are confirmed through Polarizing Optical Microscopy (POM). Transition temperatures corresponding to the individual mesophases are further verified using Differential Scanning Calorimetry (DSC). Phase diagram of two sets of binary mixtures are constructed with the aid of POM and DSC data. Optical tilt angle measurement; a primary order parameter; is calculated in smectic C phase of the binary mixtures and the resultant data obtained is fitted to critical exponent value is in concurrence with the Mean Field theory predicted value. Thermal studies such as stability factor, order of phase transitions and specific heat capacity value of the mesophases are extracted from the DSC thermograms. [ABSTRACT FROM AUTHOR]

The synthesis and mesomorphic properties of a new series of 2,4-bis(4′-npentyloxybenzoyloxy)- benzylidine-4″ -n-alkoxyaniline (DC5An) are reported. The molecular structure of compounds was confirmed by FTIR,1H-NMR,13C-NMR, mass spectroscopy and elemental analysis. The mesomorphic properties were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) measurements. All compounds of the series exhibit nematic (N) and smectic C (SmC) phases. The first four homologues (DC5A1-DC5A4) display a N mesophase, whereas the highest homologues (DC5A5-DC5A10) exhibit an enantiotropic dimorphism N and SmC phases. The mesomorphic properties of the present series are compared and discussed with other structurally related series. [ABSTRACT FROM AUTHOR]

A new side cholesterol-functionalised liquid crystal (LC) copolymer based on aliphatic polycarbonate backbone was synthesised. The chemical structures of the block copolymers obtained in this study were characterised with Fourier Transform Infrared Spectroscopy (FT-IR) and Proton Nuclear Magnetic Resonance (1H NMR) spectra. Their thermal stability and phase behaviours were investigated with thermogravimetric analysis (TGA) measurements, differential scanning calorimetry, and polarising optical microscopy. The molecular organisation in the mesophase was studied by temperature-dependent X-ray diffraction (XRD). As a result, the block copolymer bearing side cholesteryl groups showed a glass transition at 15.8°C and a smectic A (SmA) to isotropic phase transition at 151.3°C on heating cycle. XRD indicated that the block LC copolymer showed an interdigitated molecular arrangement of the mesogenic units within the smectic layers. This partial bilayer structure was similar to the SmA phase formed by polar mesogens. [ABSTRACT FROM AUTHOR]

Gel phase formation is commonplace for surfactants, lipids and oils. The most frequently encountered states are the α-gel phase for non-polar lipids such as triglycerides and the L β phase for surfactants and polar lipids. It is well known that both the L β phase and the α-gel phase consist of surfactant layers where the alkyl chains are mostly in an all-trans conformation with no translational mobility. These are packed in a two dimensional hexagonal lattice with rotational disorder (high angle X-ray peak at 4.2 Å). However, in the case of the α-gel phase for unsaturated monglycerides, the alkyl chains cannot be in the all-trans state. The high angle X-ray pattern shows a broad peak at 4.1 Å plus at ca. 4.5 Å. Clearly, this cannot pack in the same hexagonal structure as the α-gel phase of the saturated lipids, but the cis double bond can be accommodated. Limited information is available regarding the effect of saturated and unsaturated triglyceride on stability of the gel phase in aqueous system We have examined the phase behaviour of mixed saturated and unsaturated monoglycerides [glycerol monostearate (GMS) and glycerol monooleate (GMO) (1:1)] in palm oila and olive oil with water. Optical microscopy was used to study the mesomorphic behaviour as function of temperature. We also employed differential scanning calorimetry (DSC) to determine the transition enthalpies between mesophases. In parallel we use small angle X-ray diffraction to characterize the different mesomorphic phases at different temperatures. The finding of this work cast light on the phase behaviour of saturated and unsaturated monoglycerides in oil with water system, Our results suggest that saturated triglycerides promotes the stability of gel phase while unsaturated triglycerides promotes the forming of the cubic phase at room temperature From an industrial point of view, both the cubic phase and gel phase could be attractive systems for making stable products with low fat content. [ABSTRACT FROM AUTHOR]

A thieno [3,2-b] thiophene-based planar liquid crystal molecule, C12-PTTT, which possesses the characteristics of an organic field-effect transistor (OFET), was synthesised and its mesomorphic properties were studied by polarising optical microscopy and differential scanning calorimetry. A wide temperature range for a highly oriented smectic phase was observed. OFET devices made under various conditions, such as self-assembled monolayer treatment and alignment treatment, and with micro-channel structures, were fabricated to measure the electrical properties. Among different OFET device conditions, the best electric carrier mobility for C12-PTTT was 0.038 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

In this article, we report synthesis and characterization of a novel homologous series of butyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino)benzoates, CnLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and powder X-ray diffraction (XRD) studies. The ligands and their copper(II) complexes exhibit wide range of enantiotropic smectic A mesophase as confirmed by their typical optical texture under polarizing microscope. Thermal stability of the compounds is determined by thermo gravimetric analyses. DFT calculations have been performed using GAUSSIAN-09 program at B3LYP level to obtain the stable electronic structure of the ligand and its copper(II) complex. [ABSTRACT FROM PUBLISHER]

The influence of the terminal side chain and lateral nitro on mesomorphism due to the flexibility and polarity of lateral group is investigated. A new homologues series is synthesized to accomplish this aim. The C1to C3homologue are nonmesomorphic, while the rest of the homologues exhibit enantiotropic nematic and smectic properties. The texture of the nematic mesophase is of threaded, Schlieren and droplets type. All these compounds were characterized by elemental analyses and spectroscopic techniques of FTIR and1H Nuclear magnetic resonance (NMR). The phase behaviour was studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction techniques. [ABSTRACT FROM PUBLISHER]

Two homologous series of unsymmetrical alkylated chalcones and 3,5-diaryl isoxazoles, consisting of 20 members, with various n-alkyl bromides (n=2−7, 10, 12, 14, 16) have been synthesized and studied for their liquid crystalline property. Simple strategy was employed to achieve the target materials. Flexibility in the synthesized molecules is provided by attaching straight alkoxy chains, where one terminal group is fixed and other terminal group is varied. The synthesized compounds were characterized on the basis of Mass, IR and NMR spectroscopy. The stability and the range of the mesophases increased with the length of the chain on the isoxazoles. The melting point, transition temperatures and enantiotropic liquid crystal morphologies were determined by polarizing optical microscopy (POM) in conjunction with a hot stage and by differential scanning calorimetry (DSC). [ABSTRACT FROM AUTHOR]

In a series of papers published recently, we clearly demonstrated that the most important factor governing the thermal conductivity of epoxy-AlO composites is the backbone structure of the epoxy. In this study, three more epoxies based on diglycidyl ester-terminated liquid-crystalline epoxy (LCE) have been synthesized to draw conclusions regarding the effect of the epoxy backbone structure on the thermal conductivity of epoxy-alumina composites. The synthesized structures were characterized by proton nuclear magnetic resonance (H-NMR) and Fourier-transform infrared (FT-IR) spectroscopy. Differential scanning calorimetry, thermogravimetric analysis, and optical microscopy were also employed to examine the thermal and optical properties of the synthesized LCEs and the cured composites. All three LCE resins exhibited typical liquid-crystalline behaviors: clear solid crystalline state below the melting temperature ( T ), sharp crystalline melting at T , and transition to nematic phase above T with consequent isotropic phase above the isotropic temperature ( T ). The LCE resins displayed distinct nematic liquid-crystalline phase over a wide temperature range and retained liquid-crystalline phase after curing, with high thermal conductivity of the resulting composite. The thermal conductivity values ranged from 3.09 W/m-K to 3.89 W/m-K for LCE-AlO composites with 50 vol.% filler loading. The steric effect played a governing role in the difference. The neat epoxy resin thermal conductivity was obtained as 0.35 W/m-K to 0.49 W/m-K based on analysis using the Agari-Uno model. The results clearly support the objective of this study in that the thermal conductivity of the LCE-containing networks strongly depended on the epoxy backbone structure and the degree of ordering in the cured network. [ABSTRACT FROM AUTHOR]

Films of biodegradable blends of polycaprolactone (PCL) and Pluronics F68 and F127 were manufactured by an industrial thermo-mechanical process to be applied as potential delivery systems. The effects of Pluronics on the structure (mesophase organization), and thermal and mechanical properties of polycaprolactone were investigated using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), polarized optical microscopy (POM) and tensile mechanical tests. The addition of Pluronics affected the crystallization process by changing the relative amounts of crystalline, amorphous, and meso- (condis + plastic) phases. The melting transition and XRD profiles were deconvoluted to assess the individual contribution of the different crystal morphologies. Furthermore, it was found that the mechanical properties of the blends depended on the ratio and type of Pluronic. Thus, Pluronic F127 showed a larger mesophase content than its F68 counterpart with PCL and blends with enhanced ductility. [Display omitted] • Pluronic influences mesophase organization, thermal and mechanical properties of PCL. • The presence of condis and plastic mesophases in PCL/Pluronic blends was corroborated. • SAXS, DSC and XRD techniques allowed the evaluation of the crystallites organization. • Pluronic F127 demonstrates a superior compatibility with PCL against Pluronic F68. [ABSTRACT FROM AUTHOR]

Synthetic strategies were developed to prepare l-tyrosine-based ionic liquid crystals with structural variations at the carboxylic and phenolic OH groups as well as the amino functionality. Salt metathesis additionally led to counterion variation. The liquid-crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS, SAXS). The symmetrical ILC chlorides bearing the same alkyl chain at both the ester and ether but either an acyclic or cyclic guanidinium group displayed enantiotropic SmA2 mesophases with phase widths of 31-88 K irrespective of the head group. It was particularly the replacement of chloride in the acyclic guanidinium ILC by hexafluorophosphate that induced a phase change from SmA2 to Colr. This phase change was attributed to a higher curvature of the interface due to the larger anion, which increased the effective head group cross-sectional area of the amphiphilic ILC. The unsymmetrical acyclic guanidinium chlorides, bearing a constant C14 ester and variable alkyl chains on the phenolic position, formed enantiotropic SmA2 phases. The derivative with the largest difference in chain lengths, however, displayed a Colr phase, resulting from discoid aggregates of the cone-shaped guanidinium chloride. The results are discussed in terms of the packing parameters, which indicate that the phase behaviour of the thermotropic tyrosine-based ILCs shows analogies to those of lyotropic liquid crystals. [ABSTRACT FROM AUTHOR]

Two homologous series of triblock molecules of the H(CH)(CF)(CH)H and F(CF)(CH)(CF)F general formulas with n = 6, 8, 10, and 12 have been synthesized and investigated using two complementary methods: differential scanning calorimetry and polarized optical microscopy in order to investigate their thermal behavior, establish phase diagram, and calculate thermodynamic parameters of the observed phase transitions. Although different from commonly known liquid crystal materials, all the compounds studied form thermotropic liquid crystalline phases (smectic or nematic) and undergo vitrification process. [ABSTRACT FROM AUTHOR]

We have prepared and studied new series of bent-core liquid crystals based on laterally substituted 3-hydroxybenzoic acid. The physical properties of the materials were tuned by the type of lateral substitution in the vicinity of the carboxylic unit. Further modification was achieved by reorientation of connecting ester linkages in the elongating side arms and by changing the length of terminal alkyl chains. The physical properties of the materials were determined by differential scanning calorimetry (DSC), polarising optical microscopy and for selected compounds by x-ray diffraction analysis. The introduction of fluorine as lateral substituent leads to the appearance of a lamellar or columnar mesophase. On contrary, methyl- or chlorine-substituted compounds are mostly crystalline. We have found a strong correlation between the size of the lateral substituent and the mesogenicity of the studied materials. [ABSTRACT FROM PUBLISHER]

The synthesis and characterisation of three sets of symmetric dimeric compounds composed of seven-membered oxazepinedione heterocyclic rings were carried out. All the dimers possess the tetradecyl- (n = 14) alkyl side chain attached to the nitrogen atom of the oxazepinedione core. The oxazepinedione core in turn was connected with varied connecting spacers (n = 4, 6, 8, 10 and 12). The dimers were spectroscopically characterised by FT-IR,1H-NMR,13C-NMR and elemental analysis techniques. The compounds were investigated for liquid crystalline properties using differential scanning calorimetry and polarising optical microscopy with heating assembly. The precursor imines2a–eitself started exhibiting liquid crystalline SmA/tilted hexatic mesophase. Further fusion of2a–ewith maleic anhydride, succinic anhydride and phthalic anhydride gave the novel oxazepinedione-derived symmetric dimers3a–e, 4a–eand5a–erespectively. The dimers3a–eand4a–edid not exhibit any liquid crystal (LC) properties. However, the phthalic anhydride-fused oxazepinediones5a–eshow monotropic nematic liquid crystalline phase. The results indicate that the formation of mesophase is dependent on the type of fused oxazepinedione ring. [ABSTRACT FROM PUBLISHER]

Thiophene-based rodlike molecules constructed from a three phenyl ring core and terminal dialkoxy chains recognized as forked mesogens are synthesized, and their mesophase properties as well as the molecular order are investigated. The synthesized forked mesogens would serve as model compounds for tetracatenar or biforked mesogens. On the basis of the position of the thiophene link with the rest of the core, 2-substituted and 3-substituted mesogens are realized in which the length of the terminal alkoxy chains is varied. The mesophase properties are evaluated using a hot-stage polarizing microscope and differential scanning calorimetry. For both homologues, the appearance of either nematic phase alone or in conjunction with smectic C phase is noticed depending on the length of the terminal alkoxy chains. The existence of layer ordering characteristic of the smectic C phase is confirmed for a representative mesogen using variable-temperature powder X-ray diffraction. High-resolution solid-state 13C NMR measurements of C12 homologues of the two series reveal orientational order parameters of all rings of the core as well as terminal chains in the liquid crystalline phase. For both homologues, because of the asymmetry of ring I, the order parameter value is higher in contrast to ring II, ring III, and the thiophene ring. The chemical shifts and 13C-1H dipolar couplings of OCH2 carbons of the terminal dodecyloxy chains provide contrasting conformations, reflecting the orientational constraints. Furthermore, the investigations also reveal that the mesophase range and the tendency for layer ordering are higher for 3-substituted mesogens compared to 2-substituted homologues. [ABSTRACT FROM AUTHOR]