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Mesophase
Kinds of Mesophase Terms modified by Mesophase Selected AbstractsImidazolium based ionic liquid crystals: structure, photophysical and thermal behaviour of [Cnmim]Br·xH2O (n = 12, 14; x=0, 1)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2008A. Getsis Abstract The long chain imidazolium halides [Cnmim]Br·xH2O (n = 10, 12; x = 0, 1) have been synthesized and their structural and thermal behaviour together with their photophysical properties characterized. X-ray structure analyses of the monohydrates ([C12mim]Br·H2O: triclinic, P1, no. 2, Z = 2, Pearson code aP112, a = 550.0(5) pm, b = 779.4(5) pm, c = 2296.1(5) pm, , = 81.89(5)°, , = 83.76(5)°, , = 78.102(5)°, 3523 unique reflections with Io > 2,(Io), R1 = 0.0263, wR2 = 0.0652, GooF = 1.037, T = 263(2) K; [C14mim]Br,H2O: triclinic, P1, no. 2, Z = 12, Pearson code aP11, a = 549.86(8) pm, 782.09(13) pm, c = 2511.3(4) pm, , = 94.86(2)°, , = 94.39(2)°, , = 101.83(2)°, 2063 unique reflections with Io > 2,(Io), R1 = 0.0429, wR2 = 0.0690, GooF = 0.770, T = 293(2) K) show for both compounds similar bilayered structures. Sheets composed of hydrophilic structure regions constituted by positively charged imidazolium head groups, bromide anions and hydrogen bonded water alternate with hydrophobic areas formed by interdigitated long alkyl chains belonging to imidazolium cations with different orientation. Combined differential scanning calorimetry and polarizing optical microscopy shows that the monohydrates as well as the anhydrous imidazolium salts are thermotropic liquid crystals which adopt smectic mesophases. The mesophase region is larger in case of the monohydrates when compared to the anhydrous compounds indicating that water obviously stabilizes the mesophase. All compounds show an intense whitish photoluminescence with short lived (1,,1,*) and long lived (1,,3,*) transitions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] New Methylene Blue (NMB) Encapsulated in Mesoporous AlMCM-41 Material and Its Application for Amperometric Determination of Ascorbic Acid in Real SamplesELECTROANALYSIS, Issue 15 2007Shabnam Sohrabnezhad Abstract New methylene blue (NMB) dye incorporated into AlMCM-41 surfactant-free and hybrid surfactant-AlMCM-41 mesophase. UV-vis evidence shows that new methylene blue dye protonated in both cases of zeolites. New methylene blue is electroactive in zeolites and their electrochemical activity has been studied by cyclic voltammetry and compared to that of NMB in aqueous solutions. New methylene blue molecules are not released to the solution during CV measurements and are accessible to H3O+ ions. The presence of surfactant affects the kinetics of the redox process through proton ions diffusion. The midpoint potentials (Em) values show that new methylene blue dye incorporated into AlMCM-41 can be reduced easily with respect to solution new methylene blue. New methylene blue interacting with surfactant polar heads and residual Br, ions as a results, it shows a couple of peaks in high potential with respect to new methylene blue solution. The electrode made with methylene blue-AlMCM-41 without surfactant was used for the mediated oxidation of ascorbic acid. The anodic peak current observed in cyclic voltammetry was linearly dependent on the ascorbic acid concentration. The calibration plot was linear over the ascorbic acid concentration range 1.0×10,5 to 5.0×10,4 M. The detection limit of the method is 1.0×10,5 M, low enough for trace ascorbic acid determination in various real samples. [source] Design of Neutral Metallomesogens from 5,5-Dimethyldipyrromethane: Metal Ion Mediated Control of Folding and Hairpin StructuresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 32 2008Kelly A. Ames Abstract New ligands derived from 5,5-dimethyldipyrromethane and their corresponding neutral complexes with ZnII and PdII are described. The ligands incorporate either a hexacatenar [H2(1n), n = 1, 10, 12, 14 and 16], tetracatenar [H2(2n), n = 1 and 16] or an extended dicatenar structure [H2(3n), n = 1and 16]. Single-crystal X-ray structure determinations of [Zn2(11)2] and [Zn2(31)2] confirm a distorted tetrahedral geometry at ZnII to afford double-stranded helical structures, while the PdII species [Pd(31)] shows a distorted square-planar geometry with the ligand adopting an alternative hairpin conformation. The metal-free hexacatenar ligands H2(1n) (n = 10, 12, 14, 16) and the corresponding complexes [Zn2(116)2] and [Pd(1n)] (n = 12, 14, 16) are not mesomorphic. However, the tetracatenar complex [Zn2(216)2] generates a smectic mesophase, as confirmed by X-ray diffraction, while [Pd(216)] and the metal-free ligand H2(216) show no mesomorphic behaviour. Two of the extended dicatenar compounds, H2(316) and [Zn2(316)2] are non-mesomorphic, while [Pd(316)] displays a smectic A phase.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Liquid Crystal Imidazolium Salts: Towards Materials for Catalysis and Molecular ElectronicsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2007Jean-Moïse Suisse Abstract 1,3-Bis(4-alkyloxyphenyl)-3H -imidazol-1-ium trifluoromethanesulfonates, alkyl = CH3(CH2)n,1, n = 8, 10, 12, 14 and 16, can be derived from the analogous 4-alkyloxyphenylamines. These imidazolium salts exhibit a lamellar liquid-crystal mesophase between 99 °C and 191 °C. The smectic-A phase was fully characterised by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction. We report also the synthesis, lamellar crystal structure and catalytic activity of the PdII complex of the (deprotonated) carbene form of one of these salts. In addition, we measured the charged carrier mobilities in the mesophase.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Niobium Oxide Mesophases Obtained by Self-Assembly of an Aqueous Soluble Niobium Complex Precursor and Organic TemplatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2007Marcos A. Bizeto Abstract In this paper the use of triammonium trioxalato(oxido)niobate {(NH4)3[NbO(C2O4)3]} as an inorganic precursor to assemble organized hybrid niobium oxide mesophases using n -octylamine (OCT) and cetyltrimethylammonium (CTA) bromide as structure-directing agents is described for the first time. The niobium complex is water-soluble and its hydrolysis at controlled pH and in the presence of organic templates leads to the formation of hybrid mesophases. A lamellar mesophase is produced by a neutral route based on the interaction of hydrolyzed units with the octylamine micelles. On the other hand, a hexagonal (p6m) mesophase is obtained when hydrolyzed species interact with CTA micelles through a charge-matching route (ionic route). This is the first time that such an ionic route has been described for the production of organized niobium oxide hybrids.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Mixed f-d Metallomesogens with an Extended Rigid CoreEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Koen Binnemans Abstract The liquid-crystalline behaviour of copper(II) and nickel(II) complexes of a mesogenic Schiff-base ligand derived from N,N' -disalicylidene-1,2-phenylenediamine (salophenH2) and of the corresponding trinuclear mixed copper(II)/lanthanum(III) and nickel(II)/lanthanum(III) complexes was investigated. High-temperature X-ray diffraction studies revealed that both the parent transition metal complexes and the mixed f-d complexes exhibit a hexagonal columnar phase (Colh) over an extended temperature range. Complex formation with lanthanum(III) nitrate resulted in an increase of the transition temperatures. The geometrical parameters (lattice parameters and column cross-section) of all the metal complexes are very similar, which indicates that the local organisation in the mesophase is the same despite their structural differences. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Columnar Mesomorphism in Hexacatenar Tetrahedral (2,2,-Bipyridine)zinc Complexes and Homologous Palladium DerivativesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2005Giovanna Barberio Abstract The synthesis and characterisation of novel liquid crystals which display columnar mesomorphism induced upon complexation of a series of nonmesomorphic hexacatenar 4,4,-disubstituted 2,2,-bipyridines (Ln) are reported. The introduction of different metal centres (Zn, Pd) causes the appearance of mesomorphism in all complexes regardless of the geometry around the metal ion. We therefore report the first examples of mesomorphism in tetrahedral zinc derivatives. The nature of the columnar phases is related to the self-assembly of the half-disc shaped [LnMCl2] (M = Zn, Pd) complexes into full disc-shaped supramolecules. The molecular organisation in the mesophase is mainly driven by intermolecular attractive interactions, as shown by the crystal structure of the model compound [LPdCl2]. Preliminary measurements of photoconductivity have been performed on samples of [LnMCl2] complexes doped with C60 to increase absorption. Promising results were obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Adducts of Schiff Bases with Tris(,-diketonato)lanthanide(III) Complexes: Structure and Liquid-Crystalline BehaviourEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2003Koen Binnemans Abstract Adducts of the Schiff base 2-hydroxy- N -octadecyloxy-4-tetradecyloxybenzaldimine with tris(,-dibenzoylmethanato)lanthanide(III) complexes are described. The stoichiometry of the complexes is [Ln(dbm)3Lx], where Ln is a trivalent lanthanide ion (all lanthanides except Ce and Pm), Hdbm is dibenzoylmethane and L is the Schiff base; x = 2 for Ln = La,Er and x = 1 for Ln = Tm,Lu. The Schiff-base ligands are in a zwitterionic form and coordinate through the phenolic oxygen only. The X-ray single-crystal structure of [La(dbm)3L,2] with L, = N -butyl-2-hydroxy-4-methoxybenzaldimine is described. The solution structure of lanthanum(III) complexes has been investigated by 1D and 2D 1H NMR techniques. Although the long-chain Schiff-base ligand and the tris(,-dibenzoylmethanato)lanthanide(III) complexes are non-mesomorphic, some of the adducts exhibit a monotropic smectic A phase. The mesomorphic behaviour depends on the lanthanide ion, in the sense that only a mesophase is observed for the series Ln = La,Eu, not for the heavier lanthanides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] One-Dimensional Microwires Formed by the Co-Assembly of Complementary Aromatic Donors and AcceptorsADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Jie-Yu Wang Abstract A truxene derivative (Tr3) with a C3 symmetric conjugated plane is synthesized; this derivative is a perfect match, in both size and structure, with its oxidized counterpart, the truxenone derivative (TrO3), a new electron acceptor that was recently reported. The complementary pair, Tr3 and TrO3, sets a good platform for the investigation of aromatic donor,acceptor interactions. Detailed 1H NMR experiments, photoluminescence spectroscopy, as well as differential scanning calorimetry are performed to investigate the interaction between Tr3 and TrO3, from solution to mesophase. One-dimensional microbelts readily formed from a 1:1 mixture of Tr3 and TrO3. Scanning electron microscopy, powder X-ray diffraction, as well as fluorescence microscopy are performed to elucidate their co-assembly structure in the solid state. Moreover, modulation of the co-assembly structure is easily realized by changing the concentration or mixing ratio. The present system opens the possibility of forming 1D heterostructures via electron donor,acceptor interaction, and its potential application as P,N junction and photowaveguide materials in optoelectronic devices. [source] High Carrier Mobility up to 0.1,cm2,V,1,s,1 at Ambient Temperatures in Thiophene-Based Smectic Liquid Crystals,ADVANCED MATERIALS, Issue 5 2005M. Funahashi The synthesis and carrier-transport properties of oligothiophene liquid-crystalline semiconductors are reported. An asymmetrically substituted terthiophene and quaterthiophene give rise to a highly ordered smectic mesophase (see Figure) with an excellent carrier mobility of up to 0.1, cm2,V,1,s,1 over a wide mesophase temperature range, including ambient temperatures. This mobility is comparable to that of organic polycrystals. [source] The effect of disorder on the chemical reactivity of an organic solid, tetraglycine methyl ester: Change of the reaction mechanismJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2002Evgenyi Shalaev Abstract Many drugs undergo chemical changes in the solid state, and understanding chemical reactivity of organic crystals is a critical factor in the drug development process. In this report, the impact of milling on the thermal chemical reactivity of an organic solid, tetraglycine methyl ester, was studied using DSC, isothermal calorimetry, chemical analysis (HPLC and insoluble residue determination), and powder X-ray diffraction. Significant changes in both X-ray diffraction patterns and DSC curves were detected after very brief milling (5 s). The changes were interpreted as the formation of a disordered phase. The disordered phase was tentatively identified as a crystal mesophase that combines properties of both crystalline (i.e., long-range order) and amorphous (i.e., glass transition) states. In the disordered material, the reaction mechanism changed from the methyl transfer reaction, which was observed in the intact crystal, to a polycondensation reaction when the reaction was performed at 165°C. Such changes in the reaction mechanism occurred in materials milled for >,30 s. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:584,593, 2002 [source] Phase behavior and photo-responsive studies of photoactive liquid crystalline hyperbranched polyethers containing benzylidene moietyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2009V. Srinivasa Rao Abstract Two sets of hyperbranched polyether epoxies were synthesized to study the effect of substituent, rigidity, and nature of photoactive unit on the thermal and photoresponsive properties. Each set was comprised of one molecule with an acyclic moiety in the repeating unit, and two molecules with a cyclic moiety of varying rigidity (cycle size) in the repeating unit. Two substituents on aromatic rings in the repeating unit were present in one set, and other set was without a substituent. The mesogenic and photoresponsive properties were studied and correlated to the varied structural parameters. The effects of varied molecular structural parameters on phase behavior and photoresponsive properties were very prominent. Out of six monomeric diols, only four have exhibited liquid crystalline phase while the polymers corresponding to all monomeric diols revealed mesophase. The findings in photoresponsive properties were further supported by molecular modeling studies. The changes in refractive index, photoviscosity, and fluorescence intensity with irradiation time substantiated the spectral pattern observed in UV-Vis spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2774,2786, 2009 [source] Hydrogen bond-directed self-assembly of peripherally modified cyclotriphosphazenes with a homeotropic liquid crystalline phaseJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2008Jianwei Xu Abstract The synthesis and characterization of hydrogen-bonded star-shaped complexes consisting of stilbazolyloxy, azopyridyl, and Schiff base-substituted cyclotriphosphazenes (3a, 3b, and 3c, respectively) and monoalkyloxy, bis(dodecyloxy), and tris(dodecyloxy)benzoic acids are reported. The thermal behaviors of complexes are studied by the means of differential scanning calorimetry, polarizing optical microscopy, and X-ray diffractometry. Only 3a and 3b with monoalkyloxybenzoic acids show a homeotropic smectic A mesophase. The effect of azo and ethylene linkage of mesogenic groups in the cyclotriphosphazenes and the length of the flexible chain in monoalkyloxybenzoic acids on mesophase transition behaviors are investigated, revealing that the linkages in mesogenic groups governs the phase transition temperatures, and the length of flexible chain in proton donors plays an important role in controlling the magnitude of enthalpy and entropy of mesophase transitions in this supramolecular liquid crystal system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4691,4703, 2008 [source] Effect of molecular architecture and size of mesogen on phase behavior and photoactive properties of photoactive liquid crystalline hyperbranched polyester epoxies containing benzylidene moietyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2008V. Srinivasa Rao Abstract A series of photoactive liquid crystalline linear and hyperbranched polyester epoxies were synthesized by polyaddition of photoactive bis benzylidene alkanone diol monomers and terephthalic acid and trimesic acid respectively with good yield. The effect of molecular architecture (linear and hyperbranched), size of mesogenic unit (cyclic and acyclic units) on the physicochemical, thermal, mesogenic, and photoactive properties of hyperbranched polymers were studied and compared. Degree of branching of hyperbranched polymers was found to be in the range of 0.46,0.49. Monomers containing cyclic moieties only exhibited nematic mesophase, while all polymers exhibited typical nematic mesophase. Intermolecular photo cycloaddition reaction was studied by ultraviolet,visible spectra (UV,vis) and NMR spectroscopy and photo viscosity measurement of UV irradiated polymer solutions. Faster photo induced behavior of hyperbranched polymers containing acyclic alkanone moiety, as compared to polymers containing cycloalkanone moieties, was observed. The change in the refractive index was found to be in the range of 0.02,0.024. Substantial variation of refractive index indicates that this polymer could be used for optical recording. All the polymers were also found to be fluorescent in nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 552,563, 2008 [source] Lightly crosslinked, mesomorphic networks obtained through the reaction of dimeric, liquid-crystalline epoxy,imine monomers and heptanedioic acidJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2006David Ribera Abstract We reacted various dimeric, liquid-crystalline epoxy,imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid-crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed-frequency and frequency-sweep modes in the shear sandwich configuration. The arrangement in the liquid-crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid-crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid-crystalline phase with respect to side-chain liquid-crystalline elastomers and that the time,temperature superposition principle did not hold through the liquid-crystalline-to-isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270,6286, 2006 [source] Liquid-crystalline stereoregular polyketone prepared from a mesogenic vinylarene and carbon monoxideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2003Yasutoyo Kawashima Abstract Isotactic and syndiotactic polyketones were synthesized by the alternating copolymerizations of a mesogenic vinylarene, 4-cyano-4,-[8-(4-vinylphenyl)octyl-1-oxy]biphenyl, with carbon monoxide, and this revealed the influence of backbone tacticity on their thermal properties. The isotactic polyketone was an amorphous polymer that did not show any mesophase, whereas the syndiotactic polyketone exhibited liquid crystallinity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3556,3563, 2003 [source] Living free-radical polymerization (reversible addition,fragmentation chain transfer) of 6-[4-(4,-methoxyphenyl)phenoxy]hexyl methacrylate: A route to architectural control of side-chain liquid-crystalline polymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2003Xiaojuan Hao Abstract Side-chain liquid-crystalline polymers of 6-[4-(4,-methoxyphenyl)phenoxy]hexyl methacrylate with controlled molecular weights and narrow polydispersities were prepared via reversible addition,fragmentation chain transfer (RAFT) polymerization with 2-(2-cyanopropyl) dithiobenzoate as the RAFT agent. Differential scanning calorimetry studies showed that the polymers produced via the RAFT process had a narrower thermal stability range of the liquid-crystalline mesophase than the polymers formed via conventional free-radical polymerization. In addition, a chain length dependence of this stability range was found. The generated RAFT polymers displayed optical textures similar to those of polymers produced via conventional free-radical polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2949,2963, 2003 [source] Synthesis, characterization, and in vitro degradation of thermotropic polyesters and copolyesters based on terephthalic acid, 3-(4-hydroxyphenyl)propionic acid, and glycolsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2001Minoru Nagata Abstract A new series of thermotropic liquid-crystalline (LC) polyesters were prepared from a diacyl chloride derivative of 4,4,-(terephthaloyldioxy)-di-4-phenylpropionic acid (PTP) and glycols with a different number of methylene groups (n) [HO(CH2)n OH, n = 6,10, 12] by high-temperature solution polycondensation in diphenyl oxide. PTP6/10 and PTP6/hydroquinone (H) LC copolyesters were also prepared according to a similar procedure. The chemical structure, LC, phase-transition behaviors, thermal stability, and solubility were characterized by elemental analysis, Fourier transform infrared spectroscopy, 1H and 13C NMR spectra, differential scanning calorimetry (DSC), thermogravimetric analysis, and a polarizing light microscope. The melting and isotropization temperatures decreased in a zigzag manner as the number of n increased. All of the polyesters formed a nematic phase with the exception of PTP8. The temperature ranges of the mesophase (,T) were much wider for the polyesters with an odd number of n's than those with an even number. ,T increased markedly for the PTP6/10 and PTP6/H copolyesters. The in vitro degradations of the polymers were ascertained by enzymatic hydrolysis and alkaline hydrolysis. The model compound, PTP dihexylester, was synthesized and found to be degraded into terephthalic acid, 3-(4-hydroxyphenyl)propionic acid, and 1-hexanol by Rhizopus delemar lipase, but PTPn homopolyesters and PTP6/10 and PTP6/H copolyesters were resistant to Rhizopus delemar hydrolysis. They were degradable in a sodium hydroxide buffer solution of pH 12 at 60 °C, depending on the number of n's and the copolymer composition. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3043,3051, 2001 [source] Time-Resolved Synchrotron SAXS Observations on Sheared Syndiotactic Poly(propylene) Crystallization ProcessMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2008Huiying Wen Abstract The in situ crystallization kinetics of syndiotactic poly(propylene) (sPP) has been investigated by synchrotron small-angle X-ray scattering (SAXS). The structure evolutions during the isothermal crystallization of sPP with different shear rates have been observed. The results show that shear accelerates the process of crystallization kinetics. Even under low shear rate, the lamellae can be distinctly oriented. In contrast, the lamellar parameters such as the long period, lamellar thickness, and the scattering invariant Q can change obviously only under high shear rate. A mesomorphic structure proposed by Strobl is adopted to elucidate the differences of shear effects with low and high shear rates. Based on all the analysis we are convinced that a relatively stable mesomorphic structure forms before shear is composed and the shear effects on the mesophase will be retained to a certain extent until crystallization is finished. [source] Novel Triaromatic Ester Mesogenic Liquid Crystalline Epoxy Resin Containing Both Methyl Substituent and Ethoxy Flexible Spacer: Synthesis and CuringMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2008Guo-dong Liu Abstract A novel triaromatic ester liquid crystalline epoxy resin (LCER) that contains both a methyl substituent and an ethoxy flexible spacer, p -methylphenylene di{4-[(2,3-epoxypropoxy)ethoxy]benzoate} (MPEPEB), has been synthesized. The mesotropic property has been investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (POM). MPEPEB shows a lower melting temperature at 78.7,°C and a broad nematic mesophase temperature range of about 55,°C. Meanwhile MPEPEB shows a mesophase to ,50,°C upon cooling. The curing behavior of MPEPEB with 2,6-diamino-3,5-diethyltoluene (DAE) has been investigated by means of DSC and POM during isothermal and dynamic processes. Although there is little difference between the activation energies obtained from the kinetic data, a marked difference is found between the isothermal and dynamic investigation. The curing reaction in the isothermal investigation roughly obeys n- th order kinetics, while two exothermal peaks appear in the dynamic DSC curves of MPEPEB/DAE. A comparison of the isothermal and dynamic data shows that the curing rate is not a unique function of temperature and curing degree. The cured networks have lower glass temperatures and show a mesophase at room temperature which disappears at about 86,88,°C. [source] Main-Chain Liquid Crystalline Polymers Based on Bis-Etherified 9,9-Dihexyl-2,7-bis(4,-hydroxy-1,1,-biphen-4-yl)fluorenesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2007Tanja Sovi Abstract A series of liquid crystalline compounds based on 2,7-bis(biphenyl)fluorenes was synthesised by a Suzuki cross-coupling reaction and subsequent etherification with different bromoalkenes. By simple variations of the chain lengths the temperature range in which the nematic mesophase is present could be tuned. The described approach offers the possibility of covalent incorporation of the mesogens into polymers via olefin metathesis techniques, resulting in enlarged stability of the mesophase. Monomers and polymers could be easily aligned on rubbed polyimide substrates as revealed by polarised absorption spectroscopy. [source] Synchrotron X-ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p,-bibenzoate)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2003Ernesto Pérez Abstract Time-resolved synchrotron X-ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p,-bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110,°C. Moreover, the annealing of PDEB at temperatures above Tg for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained. Scattering profiles corresponding to sample PDEB85 in a melting experiment. [source] Orientated crystallization in drawn thermoplastic polyimide modified by carbon nanofibersPOLYMER ENGINEERING & SCIENCE, Issue 2 2009Valentina E. Smirnova The solid state crystallization in drawn thermoplastic polyimide films is studied as a function of draw ratio (DR) under the effect of vapor grown carbon fiber nanoinclusions. The nucleating effect of the nanoinclusions coupled with the orientation effect of drawing generates a unique orientated layered lamellar structure, characteristic of smectic-like mesophase. The degree of draw induced orientated crystallization increases with the content of nanoinclusions and with the DR, and is reflected in the mechanical behavior of the film. Generally, the Young's modulus and the yield point of the drawn crystalline films in the drawing direction are significantly higher compared with the noncrystalline counterparts. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source] Crystal structure and orientation behavior of transversely compressed poly(ethylene- co -1-octene) filamentsPOLYMER ENGINEERING & SCIENCE, Issue 12 2008Haifeng Shan A basic study on crystal structure and orientation behavior of transversely compressed ethylene-1-octene copolymer with different 1-octene contents was described. All polymers were first melt spun under different spinline stress and subsequently transversely compressed. For the melt-spun filaments, an orthorhombic crystal structure was found for all polymers, but a pseudo-hexagonal mesophase was also found for polymers with the highest 1-octene level (13.3 mol%). For the transversely compressed filaments, several reflection peaks from a monoclinic unit cell were found for polyethylene without octene. For those with higher octene levels, the reflection peaks from monoclinic became fainter and disappeared for the one with the highest 1-octene level. After being transversely compressed, the (110) and (200) peaks of orthorhombic crystal structures became oriented along the meridian direction, which is the fiber axis direction. The reason for this appears to be that the compression deformation of the filament induces elongation along its width direction and shrinkage along its length and thickness direction, and in this change the polymer chain orients. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Measurement of critical concentration for mesophase formation of chitosan derivatives in both aqueous and organic solutionsPOLYMER INTERNATIONAL, Issue 12 2006Yan-ming Dong Abstract A novel chitosan derivative, acryloyl chitosan (AcCs), and two N -maleoyl chitosans, MaCs-1 and MaCs-2, with different degrees of substitution were synthesized using completely deacetylated chitosan as raw material under different reaction conditions. AcCs is an amphiphilic chitosan derivative, but MaCs-1 and MaCs-2 are soluble in water and organic solvents respectively. The concentrated solutions of AcCs, MaCs-1 and MaCs-2 all demonstrated mesophases and were investigated using polarizing optical microscopy (POM). Circular dichroism (CD) was also employed for determining the critical concentration for mesophase formation. A broad peak in the visible light region of CD spectra had its origin in the appearance of the mesophase, and arose from the selective reflection of cholesteric helix pitches. The results of CD measurements agreed with those of POM. The critical concentration values for aqueous solutions were much lower than those for organic solutions, which was explained by the strong interactions between the chitosan derivatives and water. Copyright © 2006 Society of Chemical Industry [source] Synthesis and characterization of liquid crystalline elastomers bearing fluorinated mesogenic units and crosslinking mesogensPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2009Fan-Bao Meng Abstract Several new side-chain liquid crystalline (LC) polysiloxanes and elastomers (IP - VIP) bearing fluorinated mesogenic units and crosslinking mesogens were synthesized by a one-step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a fluorine-containing LC monomer 4,-undec-10-enoyloxy-biphenyl-4-yl 4-fluoro-benzoate and a crosslinking LC monomer 4,-(4-allyloxy-benzoxy)-biphenyl-4-yl 4-allyloxy-benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, 1H-NMR, EA, TGA, DSC, POM and XRD. The effect of crosslinking mesogens on mesomorphic properties of the fluorinated LC polymers was studied as well. The obtained polymers and elastomers were soluble in many solvents such as toluene, tetrahydrofuran, chloroform, and so forth. The temperatures at which 5% weight loss occurred (Td) were greater than 250°C for all the polymers, and the weight of residue near 600°C increased slightly with increase of the crosslinking mesogens in the fluorinated polymer systems. The samples IP, IIP, IIIP and IVP showed both smectic A and nematic phases when they were heated and cooled, but VP and VIP exhibited only a nematic mesophase. The glass transition temperature (Tg) of polymers increased slightly with increase of crosslinking mesogens in the polymer systems, but the mesophase,isotropic phase transition temperature (Ti) and smectic A,nematic mesophase transition temperature (TS-N) decreased slightly. It suggests that the temperature range of the mesophase became narrow with the increase of crosslinking mesogens for all the fluorinated polymers and elastomers. In XRD curves, the intensity of sharp reflections at low angle decreased with increase of crosslinking mesogens in the fluorinated polymers systems, indicating that the smectic order derived from fluorinated mesogenic units should be destroyed by introduction of more crosslinking mesogens. Copyright © 2008 John Wiley & Sons, Ltd. [source] Synthesis and characterization of chiral liquid-crystalline polysiloxanes containing fluorinated units and sulfonic acid groupsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2008Fan-Bao Meng Abstract Chiral side-chain liquid-crystalline polysiloxanes (PS-1, PS-2, PS-3, PS-4, PS-5, PS-6) bearing fluorinated units and sulfonic acid groups were synthesized with poly(methylhydrogeno)siloxane, cholest-5-en-3-ol(3,)-4-(2-propenyloxy)benzoate, and 3-trifluoromethyl-phenyl 3-sulfo-4-undec-10- enoyloxy-benzoate. The effects of fluorinated units and sulfonic acid groups on characteristic of liquid-crystalline properties were studied. PS-1, PS-2, and PS-3 exhibited both smectic and cholesteric mesophases, while PS-4, PS-5, and PS-6 exhibited only cholesteric mesophase. As the polymers contained more fluorinated units and sulfonic acid groups, segregation of the fluorinated segment to the surface and aggregation of hydrogen bonding should occur. Therefore, the highly ordered lamellar mesogen,siloxane matrix systems should be disturbed severely, suggesting that PS-4, PS-5, and PS-6 show no smectic phase. The maximum reflection bands become broad and shifted slightly to long wavelength from PS-1 to PS-6. Copyright © 2008 John Wiley & Sons, Ltd. [source] 4,-[2-(2-Ethoxyethoxy)ethoxy]biphenyl-4-carboxylic acid: correlation between its crystalline and smectic phasesACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Rosana S. Montani The crystal structure of the dimeric title compound, C19H22O5, is dominated by a head-to-head hydrogen-bonding interaction between centrosymmetrically related carboxyl groups in each monomer. The result is a dimeric axis of unusual length (ca 34,Å), but still shorter than what could be expected for a fully extended chain, owing to two turning points in the oligoethoxy ends. This allows for an explanation of the structure of the smectic mesophase exhibited by this compound and at the same time fully validates former geometric estimations based on PM3 calculations. [source] Overcoming merohedral twinning in crystals of bacteriorhodopsin grown in lipidic mesophaseACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Valentin Borshchevskiy Twinning is one of the most common crystal-growth defects in protein crystallography. There are neither efficient rational approaches for the growth of nontwinned protein crystals nor are there examples of systematic studies of the dependence of the twinning-ratio distribution on crystallization conditions. The description of the twinning phenomenon has been covered even less for membrane-protein crystals and is non-existent for crystals grown using lipidic phases (in meso). In the present work, possibilities for overcoming merohedral twinning are investigated for crystals of the membrane protein bacteriorhodopsin (bR) grown in meso. It is shown that traditional crystallization additives are not effective in the case of the in meso crystallization of bR. The twinning ratio was determined for 310 crystals grown under different crystallization conditions. A correlation of the twinning ratio with the growth rate of the crystals was observed. Slow growth indicated that crystals had a noticeable chance of avoiding twinning. Model calculations were performed in order to rationalize this observation. The calculations confirmed the experimental observation that most crystals consist of two twin domains and showed that under this condition small changes in the probability of twin-domain formation lead to dramatic changes in the number of nontwinned crystals, which explains why slow crystal growth results in a considerable number of nontwinned crystals. [source] Dynamic Supramolecular Polymers Based on Benzene-1,3,5-tricarboxamides: The Influence of Amide Connectivity on Aggregate Stability and Amplification of ChiralityCHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2010Patrick Abstract N-Centred benzene-1,3,5-tricarboxamides (N-BTAs) composed of chiral and achiral alkyl substituents were synthesised and their solid-state behaviour and self-assembly in dilute alkane solutions were investigated. A combination of differential scanning calorimetry (DSC), polarisation optical microscopy (POM) and X-ray diffraction revealed that the chiral N-BTA derivatives with branched 3,7-dimethyloctanoyl chains were liquid crystalline and the mesophase was assigned as Colho. In contrast, N-BTA derivatives with linear tetradecanoyl or octanoyl chains lacked a mesophase and were obtained as crystalline compounds. Variable-temperature infrared spectroscopy showed the presence of threefold, intermolecular hydrogen bonding between neighbouring molecules in the mesophase of the chiral N-BTAs. In the crystalline state at room temperature a more complicated packing between the molecules was observed. Ultraviolet and circular dichroism spectroscopy on dilute solutions of N-BTAs revealed a cooperative self-assembly behaviour of the N-BTA molecules into supramolecular polymers with preferred helicity when chiral alkyl chains were present. Both the sergeants-and-soldiers as well as the majority-rules principles were operative in stacks of N-BTAs. In fact, the self-assembly of N-BTAs resembles closely that of their carbonyl (CO)-centred counterparts, with the exception that aggregation is weaker and amplification of chirality is less pronounced. The differences in the self-assembly of N- and CO-BTAs were analysed by density functional theory (DFT) calculations. These reveal a substantially lower interaction energy between the monomeric units in the supramolecular polymers of N-BTAs. The lower interaction energy is due to the higher energy penalty for rotation around the PhNH bond compared to the PhCO bond and the diminished magnitude of dipole,dipole interactions. Finally, we observed that mixed stacks are formed in dilute solution when mixing N-BTAs and CO BTAs. [source] | |||||||||||||||||||||||||