Study on a series of main-chain liquid-crystalline ionomers containing sulfonate groups

A series of main-chain Liquid-crystalline ionomers containing sulfonate groups pendant on the polymer backbone were synthesized by an interfacial condensation reaction of 4,4'-dihydroxy-alpha,alpha'-dimethyl benzalazine, a mesogenic monomer, with brilliant yellow (BY), a sulfonate-containing monomer, and a 1/9 mixture of terephthaloyl and sebacoyl dichloride. The structures of the polymers were characterized by LR and UV spectroscopies. DSC and thermogravimetric analysis were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by a polarized optical microscope, DSC, and wide-angle X-ray diffraction. The ionomers were thermally stable to about 310 degreesC. They were thermotropic liquid-crystalline polymers (LCPs) with high mesomorphic-phase transition temperatures and exhibited broad nematic mesogenic regions of 160-170 degreesC, and they were lyotropic LCPs with willowy leaf-shaped textures in sulfuric acid. However, the thermotropic liquid-crystalline properties were somewhat weakened because the concentration of BY was more than 8%. The inherent viscosity in N-methyl-2-pyrrolidone suggested that intramolecular associations of sulfonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration. (C) 2001 John Wiley & Sons, Inc.

The effects of different alkyl substitution on the structures and properties of poly(3-alkylthiophenes)

In order to investigate the influence of different alkyl side chain substitution on the structures and properties of P3ATs, X-ray diffraction, differential scanning calorimetry (DSC), thermal gravity analysis (TGA), Fourier transform infrared spectra (FTIR) and ultraviolet-visible spectra (W-VIS) were applied to characterizing the samples of ploy(3-octylthiophene) (P3OT), poly(3-dodecylthiophene) (P3DDT) and poly(3-octadecylthiophene) (P3ODT). It is found that the different length of alkyl group substitution leads to great difference in molecular chain packings, according to the room temperature X-ray diffraction results. The temperature dependence of X-ray diffraction experiments were also performed to study the melting processes of P3ATs. With the increase in the number of carbon atoms in alkyl side chains, the melting point decreases, and the thermal stability decreases too. The results of both FTIR and W-VIS spectra indicate that the conjugation length of P3DDT is the longest. among the three P3ATs. (C) 2001 Elsevier Science B.V. All rights reserved.

Size-affected crystallization of trans-1,4-polybutadiene

By using different catalyst systems, two trans-1,4-polybutadiene (TPBD) samples with different tr trans-content and molecular weight were synthesized. The phase transition of two samples from monoclinic form to hexagonal phase was revealed by differential calorimeter scanning and X-ray, respectively. The small-angle X-ray scattering measurements showed the remarkable discrepancy of phase transition and melting point between the two samples was attributed to the different lamellar thickness of crystals: The crystals with different crystalline morphology and lamellar thickness were developed by casting different concentration TPBD solutions. Transmission electron microscopy morphology observations proved that annealing the specimen at the temperature above the phase transition point for different times resulted in the different lamellae thickening of monoclinic form. It means that annealing the TPBD in its hexagonal phase will also slightly favor the increase of both the phase transition temperature and melting point of hexagonal phase. (C) 2001 Elsevier Science Ltd. All rights reserved.

Oxidation of NADH by dopamine incorporated in lipid film cast onto a glassy carbon electrode

Stable lipid film was made by casting lipid in chloroform onto a glassy carbon electrode. This model of a biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by dopamine. After this electrode had been immersed in dopamine solution for 10 h, it was found that some dopamine had been incorporated in the film. The cyclic voltammogram was obtained for the oxidation of 2.0 X 10(-3) mol 1(-1) NADH with dopamine incorporated in the films. All electrochemical experiments were performed in 0.005 mol 1(-1) phosphate buffer (pH 7.0) containing 0.1 mol 1(-1) NaCl without oxygen. The oxidation current increased gradually with successive sweeps and reached steady state. It was a different phenomenon from previous results. The anodic overpotential was reduced by about 130 mV compared with that obtained at a bare glassy carbon electrode. The diffusion coefficient for 2.0 X 10(-3) mol 1(-1) NADH was 6.7 X 10(-6) cm(2) s(-1). (C) 1999 Elsevier Science S.A. All rights reserved.

Potential-dependent adsorption/desorption of organic adsorbate at HOPG electrode and accompanying delamination of graphite surface

In situ electrochemical scanning tunneling microscopy, alternating current voltammetry, and electrochemical quartz crystal microbalance have been employed to follow the potential-dependent adsorption/desorption processes of nucleic acid bases on highly oriented pyrolytic graphite (HOPG) electrode. The results show that (i) potential-dependent adsorption/desorption of nucleic acid bases on HOPG electrode was accompanied by delamination of the HOPG surface, and the delamination initiates from steps or kinks on the electrode surface, which provide highly active sites for adsorption; (ii) the delamination usually occurred when the electrode potential was changed or when the electrode was at potentials where the phase transition of adsorbate occurred. These results suggest that the surface stress resulting from the interaction between the substrate and adsorbate, as well as the interaction due to potential-induced surface charge distribution and the hysteresis of charge equilibrium are the main factors resulting in HOPG delamination. (C) 1999 The Electrochemical Society. S0013-4651(97)12-013-4. All rights reserved.

Synthesis and characterization of thermotropic liquid crystalline poly(ester imide)s

Two closely series of poly(ester imide)s had been synthesized by solution polycondensation of p-phenylenebis(trimellitate) dianhydride with aliphatic diamines. The differential scanning calorimetry (DSC) traces of the most poly(ester imide)s exhibited two endotherms representing the solid state to anisotropic phase transition (T-m1) and the anisotropic to isotropic melt transition (T-m2), respectively. Observation under polarizing microscope and wide-angle X-ray diffraction (WAXD) measurements suggested that the anisotropic phase formed above the melting paints (T-m1) had a smectic character. The thermogravimetric analyses (TGA) revealed that the thermal stabilities of the poly(ester imide)s were up to 350 degrees C. (C) 1999 John Wiley & Sons, Inc.

Crystal growth and TG-DTA properties of K(2)Ln(NO3)(5).2H(2)O (Ln = La, Ce, Pr, Nd, Sm)

Single crystals of KLnN(Ln=La, Ce, Pr, Nd, Sm) can be grown in water solution with pH approximate to 1 similar to 2 at about 40 degrees C. Crystals of KLnN (Ln=La, Ce, Pr, Nd) are orthorhombic with space group Fdd2. KPrN crystal was grwon and its crystal structure was determined for the first time. The KPrN crystal parameters obtained by the direct method are as follows: a=21.411(3) Angstrom, b=11.2210(10)Angstrom, c=12.208(2) Angstrom, Z=6, R=0.0240. The TG-DTA curves of KLnN(Ln=La,Ce, Pr, Nd, Sm) demonstrate that the processes of dehydration, melt, irreversible phase transition and decomposition of NO3- take place in sequence with the temperature increasing(except KCN). There are three steps in the decomposition of NO3- in KLnN(Ln=La, Nd, Sm) while two steps in KLnN (Ln=Ce, Pr). K(2)Ln(NO3)(5). 2H(2)O are formed at about 225 degrees C by the reaction of the starting materials of KNO3 and Ln(NO3)(3). nH(2)O.

Synthesis and characterization of the side chain liquid crystalline poly(monoester {6-[4-(p-nitrophenyl)azo]phenoxy-1-hexyloxy} of maleic anhydride)

The poly(monoester (6-[4-(p-nitrophenyl) azo]phenoxy-1-hexyloxy) of maleic anhydride) shows a smectic phase with a focal conic fan texture. With the decrease of the monoestering degree the phase transition temperature decreases and the mesomorphic temperature range becomes narrow. The hydrogen bonding between two carboxylic acid groups was found to play a very important role in forming the smectic phase structure. The smectic bilayer structure has been built through self-assembly via. intermolecular hydrogen bonding.

SYNTHESIS OF A NEW CHIRAL LIQUID-CRYSTAL WITH SCHIFF-BASE GROUP AND INVESTIGATION OF TEMPERATURE-DEPENDING FTIR SPECTRA

A new chiral liquid crystal with Schiff base group has been prepared, The structure of liquid crystal was confirmed by elementary analyses and H-1 NMR. Its phase transition was investigated by polarized optical microscope, DSC and temperature-depending FTIR spectra. The results showed that the chiral Schiff base showed monotropic phases behavior in certain temperature range, the phase sequence is I-N-*-S-B-S-G-K on the cooling sequence.

AN INFRARED SPECTROSCOPIC CHARACTERIZATION OF THE SOLID SOLID BEHAVIOR OF DODECYLAMMONIUM CHLORIDE

The infrared spectra of the bilayer system dodecylammonium chloride has been studied as a function of temperature. Unusual splitting of some vibrational modes helps us to characterize the structure of different solid states. This study provided the evidence for the occurrence of an order-disorder phase transition whose onset occurs at 327 K and its completion ends at 339 K. In the low temperature phase below 327 K, the virgin crystals form a well-ordered phase with all-transhydrocarbon chains. In the intermediate state between 327 and 339 K, the data demonstrate the introduction of intramolecular as well as intermolecular disorder. The coexistence of solid and liquid-crystal-like states is shown by the persistence of factor group splittings together with the existence of defect bands in the wide intermediate temperature range. In the high temperature phase over 339 K the crystals convert to a liquid-crystal-like system with extensive motional and conformational disorder, but still show characteristics in their infrared spectra which indicate the presence of ordered segments in the hexagonal solid phase.

THERMAL ANALYSIS AND INFRARED SPECTRA OF DIALKYLAMMONIUM TETRAC HLOROCUPRATE

The thermal stability and the solid solid phase transitions in Ills compounds with n = 7-12 have been studied by DSC and TG methods. Comparision with CnZn compounds want made. The nature of three phases of CnCu has been discussed in terms of infrared spectroscopy and the assignment of the phase transitions has been given. The thermal stability of CnCu is lower than that of CnZn and presents an obvious odd even effect. All of these compounds exhibit two solid solid phase transitions in the temperature range of 248-337 K. The peak tempe nature of phase transitions changes regularly. The peak temperature or the main phase transition increases with the chain length. The total transition enthalpies and entropies increase with increasing chain length. When n <= 9, the high temperature phase exists in a partial disorder state. When n >= 10, the high temperature phase exists in a conformational disorder state. The main phase transition and the phase transition at 307.7 K of CnCu may mainly are from the change of the packing structure and the change of the partial conformational order-disorder of alkyl chain, respectively.

STUDY ON LOW-FREQUENCY RAMAN SPECTRA OF n-DECYLAMMONIUM CHLORIDE

The low-frequency Raman spectrum of n-decylammonium chloride was measured as a function of temperature in the temperature range from 290 to 340K, and the longitudinal acoustical mode vibration band was assigned. The results showed that there are two phase transitions at 313K and 321K, respectively. The phase transition at 313K is mainly induced by change of hydrocarbon chain conformations, while that at 321K is mainly induced by change of order degree of molecular packing. The results suggest low-frequency Raman spectroscopy is a useful probe of structural phase transition for long-chain compounds.

Mixed-layer water oscillations in tropical Pacific for ENSO cycle

The main modes of interannal variabilities of thermocline and sea surface wind stress in the tropical Pacific and their interactions are investigated, which show the following results. (1) The thermocline anomalies in the tropical Pacific have a zonal dipole pattern with 160 W as its axis and a meridional seesaw pattern with 6-8 degrees N as its transverse axis. The meridional oscillation has a phase lag of about 90 to the zonal oscillation, both oscillations get together to form the El Nino/La Nina cycle, which behaves as a mixed layer water oscillates anticlockwise within the tropical Pacific basin between equator and 12 degrees N. (2) There are two main patterns of wind stress anomalies in the tropical Pacific, of which the first component caused by trade wind anomaly is characterized by the zonal wind stress anomalies and its corresponding divergences field in the equatorial Pacific, and the abnormal cross- equatorial flow wind stress and its corresponding divergence field, which has a sign opposite to that of the equatorial region, in the off-equator of the tropical North Pacific, and the second component represents the wind stress anomalies and corresponding divergences caused by the ITCZ anomaly. (3) The trade winds anomaly plays a decisive role in the strength and phase transition of the ENSO cycle, which results in the sea level tilting, provides an initial potential energy to the mixed layer water oscillation, and causes the opposite thermocline displacement between the west side and east side of the equator and also between the equator and 12 degrees N of the North Pacific basin, therefore determines the amplitude and route for ENSO cycle. The ITCZ anomaly has some effects on the phase transition. (4) The thermal anomaly of the tropical western Pacific causes the wind stress anomaly and extends eastward along the equator accompanied with the mixed layer water oscillation in the equatorial Pacific, which causes the trade winds anomaly and produces the anomalous wind stress and the corresponding divergence in favor to conduce the oscillation, which in turn intensifies the oscillation. The coupled system of ocean-atmosphere interactions and the inertia gravity of the mixed layer water oscillation provide together a phase-switching mechanism and interannual memory for the ENSO cycle. In conclusion, the ENSO cycle essentially is an inertial oscillation of the mixed layer water induced by both the trade winds anomaly and the coupled ocean-atmosphere interaction in the tropical Pacific basin between the equator and 12 degrees N. When the force produced by the coupled ocean-atmosphere interaction is larger than or equal to the resistance caused by the mixed layer water oscillation, the oscillation will be stronger or maintain as it is, while when the force is less than the resistance, the oscillation will be weaker, even break.

塑料压力管道热板焊接接头瞬时应力有限元分析

基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用有限元软件ANSYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯塑料压力管道热板焊接过程。并对焊接接头的应力分布进行有限元分析,得到了环向、轴向及径向瞬态应力分布规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本吻合。

高密度聚乙烯塑料压力管道热板焊接头应力分布有限元分析

基于热粘弹性积分型本构关系,考虑材料性能依赖于温度变化及相变潜热的影响,利用AN SYS热-力耦合及载荷步功能模拟结晶型高密度聚乙烯(HDPE)塑料压力管道热板焊接过程,并对焊接接头的应力分布进行有限元分析,得到了环向、轴向以及径向瞬态应力分布的基本规律。采用盲孔法和锯切法测量焊后残余应力,实测结果与数值分析基本符合