Thermal behaviour of the system lead(II) dodecanoate/lead acetate

Data are presented for the heats and entropies of phase changes for the system lead(II) dodecanoate/lead acetate. A phase diagram has also been constructed for the system.Optical observation under a polarising microscope suggests that the phase sequence in this system is the same as in pure lead dodecanoate i.e. crystal → G (smectic) → V₂ (cubic isomorphous) → liquid.The entropy of the V₂ → liquid transition in the mixtures is the same as for pure lead dodecanoate which suggests that addition of lead acetate to lead dodecanoate does not affect the state of aggregation of the soap in the liquid phase.     

The molten phase conductance and the thermotropic phase transition in lead(II), zinc(II) and cadmium(II) 10-hydroxyoctadecanoates

The electrical conductances and heats of phase changes in lead(II), zinc(II) and cadmium(II) 10-hydroxyoctadecanoates are measured. The soaps are prepared by metathesis in alcohol solution from 10-hydroxyoctadecanoic acid which in turn is prepared from the oxidation of cis-9-octadecenoic (oleic) acid with concentrated sulphuric acid.The Arrhenius plot for lead(II) 10-hydroxyoctadecanoate shows a maximum, a behaviour that had earlier been interpreted to be due to complex formation. A similar plot for zinc(II) 10-hydroxyoctadecanoate is linear while that for cadmium(II) 10-hydroxyoctadecanoate presents a discontinuity which is interpreted, with the aid of the differential scanning calorimetric (DSC) spectra and optical examination, to be suggestive of the formation of an intermediate phase between the solid and the liquid phases. The low conductances of the soaps in comparison with the literature data on some metal caboxylates indicate the existence of extensive intermolecular hydrogen bonding in the molten phase. Both lead(II) and zinc(II) 10-hydroxyoctadecanoates melt directly from the solid to the liquid phase while their cadmium(II) counterpart passes through the gel-like phase before melting into the liquid. The mesophase of cadmium(II) 10-hydroxyoctadecanoate is transformed to the liquid phase with a relatively low enthalpy change and the behaviour is associated with the cylindrical micekkar structures of the liquid phase that have their formative stage from the gel-like mesophase.     

Phase transition of syndiotactic polypropylene in electrospun nanofibers during progressive heating

By means of high-temperature electrospinning process, syndiotactic polypropylene (sPP) nanofibers with an average diameter of 127 nm were obtained using a rotating disc as a collector. The aligned fibers were subjected to progressive heating for fiber melting. During heating, structural evolution of the sPP nanofibers was investigated in situ by means of two-dimensional wide-angle and small-angle X-ray scattering with synchrotron radiation sources. It was found that the as-spun fibers consist of the antichiral form I (9 %), mesophase (31 %), and amorphous phase (60 %), in the absence of isochiral form II. Upon heating, the mesophase started to melt and completely disappeared at 90 °C. The melting of the mesophase directly produced amorphous chains at 35–60 °C, and brought up the isochiral form II at low temperatures (60–70 °C), as well as the antichiral form I at high temperatures (70–110 °C). These events were in accordance with the DSC heating curve, which exhibited a small endotherm centered at 52 °C for the mesophase melting, followed by a shallow and broad exotherm associated with two phase-transition events, i.e., the crystal reorganization and the crystallization of supercooled liquid. The former is likely due to the solid–solid transition of meso→II phase as suggested by Lotz et al. (Macromolecules 31:9253, 1998), and the latter is relevant with crystallization of amorphous chains to develop the thermodynamic stable form I phase at high temperatures.     

Influence of chirality on the mesophase of side chain polymers with phenyl benzoate pendant groups

To reveal the structure of an amorphous mesophase with a hidden liquid crystalline structure (ISm*) in a chiral side chain polymer, P8*M, its racemic isomer has been synthesized along with two more RS-copolymers with controlled enantiomer excess. The phase behaviour of the copolymers was studied comparatively by DSC and X-ray scattering. Optical rotatory dichroism was measured for thin films of P8*M and two homologue polymers, differing in the polymeric main chain, by the size of the chiral terminal group and by its absolute configuration. A helical superstructure with pitch of about 250 nm is indicated within the ISm* mesophase. Its structure as a short pitch TGB phase hase been proven conclusively.     

Influence of chirality on the mesophase of side chain polymers with phenyl benzoate pendant groups

To reveal the structure of an amorphous mesophase with a hidden liquid crystalline structure (ISm*) in a chiral side chain polymer, P8*M, its racemic isomer has been synthesized along with two more RS‐copolymers with controlled enantiomer excess. The phase behaviour of the copolymers was studied comparatively by DSC and X‐ray scattering. Optical rotatory dichroism was measured for thin films of P8*M and two homologue polymers, differing in the polymeric main chain, by the size of the chiral terminal group and by its absolute configuration. A helical superstructure with pitch of about 250?nm is indicated within the ISm* mesophase. Its structure as a short pitch TGB phase hase been proven conclusively.     

The influence of charge-transfer interactions on solid and cholesteric liquid crystalline mixtures of cholesteryl anthraquinone-2-carboxylate and cholesteryl 9,10-dimethoxyanthracene-2-carboxylate

The phase behaviour of 3beta-cholesteryl 9,10-anthraquinone-2-carboxylate (CAQ, an excellent electron acceptor) and 3beta-cholesteryl 9,10-dimethoxyanthracene-2-carboxylate (CMAQ, an excellent electron donor) have been investigated neat and as mixtures by a variety of techniques. Both molecules form thermotropic cholesteric phases. UV-Vis absorption spectra of CAQ:CMAQ mixtures provide strong evidence for the formation of charge-transfer (CT) complexes in the solid state. DSC thermograms of the mixtures reveal several transitions, only some of which are observable by optical microscopy. The mesophase range of CAQ is increased by c. 40 upon addition of as little as 10 wt% of CMAQ as a consequence of increased attractive forces in the CT complexes. X-ray powder diffraction patterns confirm that CAQ forms different crystalline phases upon being cooled from the mesophase and by recrystallization from solvents. The 5:5 mixture can be supercooled to a glass from its cholesteric phase. Some of the phase behaviour of the CAQ:CMAQ mixtures is explained with a model that includes selective crystallization of the two components into eutectics from supercooled liquid crystalline matrices.     

Solution behaviour in alcohols and phase transitions of cadmium(II), mercury(II) and lead(II) carboxylates

Data were obtained for the solution behaviour of cadmium(II) and mercury(II) carboxylates in alcohols. A brief survey of the arguments about the existence of micelles and the current models of surfactant aggregation in non-aqueous media is presented. The plots of solubility against the carboxylate or alcohol chain length are linear for both cadmium and mercury soaps with the solubility having values higher in secondary than primary alcohols. The solution behaviour of metal 9, 10-dihydroxyoctadecanoates shows the effect on solubility, of substitution of dihydroxyl groups at the middle of the carbon chain. Recrystallisation temperatures of the dihydroxyoctadecanoates suggest the loss of stereochemical configuration in solution and indicate similarity in the mode of aggregation. The solution temperatures of cadmium soaps are very close to the temperatures of their phase transitions while those of mercury and lead soaps are lower than their fusion or phase transition temperatures. This behaviour is interpreted to be due to differences in the energy required for the disruption of the crystal structure which dominates the solubility mechanism.     

Mesomorphic Schiff base amine tethered giant gold nanoparticles

GNP-LC hybrid incorporating giant gold nanoclusters was accessed with tailor made liquid crystalline Schiff base bearing amine function as reactive end group without using any external reducing agent. The liquid crystal phase (smectic C) of the Schiff base remained unaltered in the hybrid material. The ligand and hybrid both exhibited interesting concentration-dependent fluorescence quenching of 9,10-diphenylanthracene when excited at 345 nm wavelength in dichloromethane solution. The GNP-LC hybrid exhibited reasonably good electrical conductivity showing an Arrhenius-type behaviour in the smectic mesophase and a tunnelling behaviour in the crystalline state.     

Solvent-free polycondensation of 1,3-bis(hydroxyphenylmethyl)benzene. II. The dramatic difference in the polymerization behavior between meso and racemic isomers

The meso and racemic forms of 1,3-bis(hydroxyphenylmethyl)benzene underwent solvent-free polycondensation with the aid of an acid catalyst giving polyether. Very interestingly, the diastereoisomerism caused a considerable difference in the polymerization behavior. The meso isomer (mp = 96–98 °C) was polymerized even at 65 °C, whereas the racemic one (mp = 158–160 °C) required heating at 100 °C to undergo polymerization. However, the latter produced a much higher molecular weight than the former (30,000 vs 4000). The contamination of the meso isomer with the racemic one very sensitively reduced the polymerization temperature: the 98.5% meso monomer underwent polymerization at 50 °C. In contrast to solvent-free polymerization, two diastereomeric monomers showed almost identical behavior in solution polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3564–3571, 2003     

Properties of molten carboxylates

Data are presented for the heats of phase changes and specific heats for the even chain length lead(II) carboxylates from hexanoate to octadecanoate. Structures are proposed by analogy to the properties of “fused” aqueous ampiphilic mesophases. Optical examination under a polarising microscope suggests the phase sequence

for the dodecanoate and lower chain length soaps. For tetradecanoate, and above, the V₂ phase is absent and the G phase melts directly to the liquid. The chain length dependence of the entropies of the crystal→G and G→V₂ or G→liquid transitions demonstrates that disordering of the hydrocarbon chain is a stepwise process. The entropy of the V₂→liquid transition is consistent with the melting of a globular solid and may indicate an average micelle size of 4 carboxylate molecules. This leads to a model of the isotropic liquid consistent with the viscosity data previously presented².     

Reductive dimerization of alkylidenemalonates using samarium(II) diiodide and 1H-NMR behavior of the dimers, 2,3-diaryl-1,1,4,4-butanetetracarboxylates

Alkylidenemalonates were readily dimerized in the presence of SmI2 to give 2,3-disubstituted 1,1,4,4-butanetetracarboxylates as mixtures of meso and racemic isomers in moderate to good yields. The structure of the less polar isomer of tetraethyl 2,3-diphenyl-1,1,4,4-butanetetracarboxylate was determined by X-ray crystallographic analysis to be the meso form. Characteristic 1H-NMR behavior of the meso and racemic isomers is also discussed.     

A monotropic liquid crystal polyester with a biphasic nematic-smectic phase

The polyesters made from the condensation of isophthalic acid (IA) or terephthalic acid (TA) with the mesogenic diol 4,4′-bis (6-hydroxy hexoxy)biphenyl (BHHBP) are both reported to show a smectic mesophase. However, in our previous work, we found evidence for a mesophase in the polyester containing BHHBP and IA, but not in the one with BHHBP and TA. For the BHHBP-IA polyester, we thought the phase sequence on cooling was I → S_A → K, while on heating the situation was unresolved; there was some indication that on heating, a K → I transition occurs without any intervening mesophase. In other words, it was suspected that the mesophase in the IA polyester was monotropic. In this work, we have now obtained firm evidence that the mesophase behavior of the BHHBP-IA polyester is indeed monotropic. Further, an additional complexity has been found: on cooling, there is in fact a nematic phase, besides a smectic A, and a crystal phase. However, the mesophase appears to be complex. As the nematic and smectic textures occurred simultaneously, it seems that the mesophase is a nematic-smectic biphase. © 1996 John Wiley & Sons, Inc.     

The role of calorimetry in the structural study of mesophases and their glass states

Four mesomorphic states of matter are known: liquid crystal, plastic crystal, condis phase, and rotator phase, all of them are solid phases, except liquid crystal, which is fluid. Plastic crystal (also called ODIC, orientational disordered crystal), rotator phase, and even condis phase have been considered the same phase by many authors. Differences between them will be established to define their own characteristics. Two organic salts series have been used for discussion in this presentation: (1) thallium(I) alkanoate series, that presents a condis mesophase, and (2) lead(II) alkanoate series, that present a rotator one, both forming a smectic A-like liquid crystal phase. Based in the literature data of the alkyl ammonium bromide series it can be established that the short chain length members would present a rotator phase, and, the large chain ones, a condis phase. Five different glass states are known (four with partial crystalline order), corresponding with the above mentioned mesophases, and the ordinary (amorphous) glass state.     

Molecular dynamics and conformational behaviour of mesogenic resorcinarenes

The dynamic and conformational behaviour of four mesogenic resorcinarenes exhibiting columnar mesophases have been studied by a combination of broadband dielectric spectroscopy and deuterium solid state NMR. Broadband dielectric spectroscopy provided evidence for two relaxation processes present both in the mesophase and in the isotropic liquid. The high frequency process II, common to all mesogens, has been assigned to the libration of the carbonyl groups of the ester junctions between the core and the side chains. The low frequency process I, present in conformationally mobile mesogens 1 and 2, has been attributed to the ring inversion process of the macrocyclic core associated with dipole inversion along the columnar axis. Deuterium solid state NMR performed on 4, the deuteriated analogue of 1, confirmed the molecular dynamics attribution for process I, assigning the ring inversion to the interconversion of the two equivalent crown conformations.     

Molecular dynamics and conformational behaviour of mesogenic resorcinarenes

The dynamic and conformational behaviour of four mesogenic resorcinarenes exhibiting columnar mesophases have been studied by a combination of broadband dielectric spectroscopy and deuterium solid state NMR. Broadband dielectric spectroscopy provided evidence for two relaxation processes present both in the mesophase and in the isotropic liquid. The high frequency process II, common to all mesogens, has been assigned to the libration of the carbonyl groups of the ester junctions between the core and the side chains. The low frequency process I, present in conformationally mobile mesogens 1 and 2 , has been attributed to the ring inversion process of the macrocyclic core associated with dipole inversion along the columnar axis. Deuterium solid state NMR performed on 4 , the deuteriated analogue of 1 , confirmed the molecular dynamics attribution for process I, assigning the ring inversion to the interconversion of the two equivalent crown conformations.     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

 用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

Unusual mesomorphic behaviour in bent-core compounds derived from 5-cyanoresorcinol

We describe the synthesis and mesomorphic properties of the first two homologous series of bent-core compounds derived from 5-cyanoresorcinol. The lower homologues in both series show a normal B₁ phase, and the mesophase of higher homologues exhibits very unusual textures and electro-optical switching behaviour. The observation of spiral growth patterns under a polarizing microscope, and only layer reflections from X-ray diffraction studies for these homologues, suggests that this mesophase is different from a B₂ phase. This mesophase shows chiral domains of opposite handedness which can be identified from electric field experiments. Under a triangular-wave electric field, at lower voltages although the mesophase shows a ferroelectric type switching behaviour it is actually antiferroelectric in nature. The observation of helical structures and spontaneously formed chiral domains suggests that the mesophase is a variant of the B₂ phase.     

Temperature dependent smectic mesophase ordering in fluorocarbon side chain polyesters

Smectic mesophase behaviour in perfluorooctyl side chain polyesters with hydrocarbon comonomers has been investigated by DETA and X-ray diffraction at different temperatures. The polymers show clear transitions from the solid to the fluid mesophase and from the mesophase to the isotropic liquid.     

Nematic and smectic mesophases in a new series of Cu(II) organometallic complexes

The synthesis and the phase behaviour of a homologous series of copper, bis[N-[[4-[4-(alkoxy)benzoyloxy],2-hydroxyphenyl]methylene]-methanamino] complexes is reported. They all exhibit thermotropic mesomorphism. The thermal stability range of the mesophase decreases slightly with increasing length of the alkoxy terminals. With the onset of smectic mesomorphism, for alkoxy groups containing ten carbon atoms, the stability interval of the nematic phase decreases progressively so that the compound containing 14 carbon atoms in the alkoxy terminal chains exhibits only smectic mesomorphism. Optical texture analysis suggests the smectic C nature of the phase in all cases. The enthalpies for the liquid crystal-isotropic transition have been measured and they are comparatively low. Remarkably low values have also been measured for the melting enthalpies of the smectogenic members of the series. These are associated with solid phase polymorphism which is discussed briefly.