Isothermal and nonisothermal crystallization kinetics of nylon-46

Isothermal and nonisothermal crystallization kinetics of nylon-46 were investigated with differential scanning calorimetry. The equilibrium melting enthalpy and the equilibrium melting temperature of nylon-46 were determined to be 155.58 J/g and 307.10 degreesC, respectively. The isothermal crystallization process was described by the Avrami equation. The lateral surface free energy and the end surface free energy of nylon-46 were calculated to be 8.28 and 138.54 erg/cm(2), respectively. The work of chain folding was determined to be 7.12 kcal/mol. The activation energies were determined to be 568.25 and 337.80 kJ/mol for isothermal and nonisothermal crystallization, respectively. A convenient method was applied to describe the nonisothermal crystallization kinetics of nylon-46 by a combination of the Avrami and Ozawa equations.

拟除虫菊酯类农药结构/急性毒性的三维定量构效关系

用比较分子力场分析(CoMFA)研究了拟除虫菊酯类农药的结构与急性毒性DL50(大鼠,口服)的关系,考察了网格结构和探针原子对结果的影响。得到模型的R2为0 99,标准偏差为0 88,说明立体效应和静电作用场是描述拟除虫菊酯类农药急性毒性和进行结构活性关系研究的重要结构参数。在模型中,立体能与静电能的贡献为0 82/0 18,说明起主要作用的是立体项,建立三维定量构效关系模型可以对该类新化合物的DL50进行预测。构建的三维结构/毒性模型用三维等高图来表示,如果结合分子杀虫活性的相关研究,可以用来指导新分子的结构设计。

Degradation of polyimide induced by nitrogen laser irradiation

The degradation behavior of polyimide (PMDA-ODA) induced by nitrogen laser irradiation was studied. The changes in the surface morphology and the composition of the irradiated polyimide films were examined by scanning electron microscopy, X-ray photoelectron spectroscopy and FT-IR spectroscopy. The initial reaction was achieved by photochemical degradation of polyimide in the highly electronic excited state by the absorption of a second 337 nm photon. Atmospheric oxygen sequentially reacted with the produced radicals to form a highly oxidized layer. The formation of carbonyl group was enhanced by the heat remaining on the irradiated polyimide film surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.

Processible nanomaterials with high conductivity and magnetizability. Preparation and properties of maghemite/polyaniline nanocomposite films

A versatile process employing anionic surfactants has been developed for the preparation of processible nanocomposite films with electrical conductivity and magnetic susceptibility. Maghemite (g-Fe2O3) nanoclusters (similar to 10 nm in size) are coated with 4-dodecyl- benzenesulfonic acid, and polyaniline (PAn) chains are doped with 10-camphorsulfonic acid. The coated nanoclusters and doped polymers are soluble in common solvents, and casting the solutions readily gives free-standing nanocomposite films with nanocluster contents as high as similar to 50 wt %. The g-Fe2O3/PAn nanocomposites show high conductivity (82-337 S cm(-1)) and magnetizability (up to similar to 35 emu/g g-Fe2O3).

Sol-gel-derived carbon ceramic electrode containing 9,10-phenanthrenequinone, and its electrocatalytic activity toward iodate

9,10-Phenanthrenequinone (PQ) supported on graphite powder by adsorption was dispersed in propyltrimethoxysilane-derived gels to yield a conductive composite which was used as electrode material to fabricate a PQ-modified carbon ceramic electrode. In this configuration, PQ acts as a catalyst, graphite powder guarantees conductivity by percolation, the silicate provides a rigid porous backbone, and the propyl groups endow hydrophobicity and thus limit the wetting region of the modified electrode. Square-wave voltammetry was exploited to investigate the pH-dependent electrochemical behavior of the composite electrode and an almost Nernstian response was obtained from pH 0.42 to 6.84. Because the chemically modified electrode can electrocatalyze the reduction of iodate in acidic aqueous solution (pH 2.45), it was used as an amperometric sensor for the determination of iodate in table salt. The advantages of the electrode are that it can be polished in the event of surface fouling, it is simple to prepare, has excellent chemical and mechanical stability, and the reproducibility of surface-renewal is good.

Excimer formation in uniaxially stretched polymer films

The steady-state fluorescence properties of naphthalene-labeled polymers dispersed in poly(methyl methacrylate) (PMMA) cast films were studied under tensile loadings at 80 degreesC. The labeled polymers were composed of methyl methacrylate (MMA) and 1-naphthylmethyl methacrylate (NMMA). Three of the copolymers were used in this work, and the contents of NMMA were 0.59 mol % (CP1), 22.0 mol % (CP2), and 56.7 mol % (CP3), respectively. The fluorescence spectra of the films containing CP1 and CP2were unchanged during elongation. For the film containing CP3, the excited monomer emission of naphthyl groups at around 337 nm decreased with increasing applied tensile strain. The strain enhanced the emission ascribed to the excimer of the naphthyl groups in the region of 390-420 nm. The ratio of fluorescence intensities at 400 nm and 337 mn, I-400/I-337, increased with the applied strain, which indicates that CP3 is a sensitive probe for detecting the structural changes of polymer matrices. The obtained results mean that the excimer-forming sites in the PMMA films during elongation depend both on the applied strain and the concentration of naphthyl groups in the dispersed polymer probes. (C) 2001 John Wiley & Sons, Inc.

Studies on the structure and properties of thermotropic liquid crystalline poly(aryl ether ketone)s

Series of thermotropic liquid crystalline poly (aryl ether ketone) s were synthesized by mucleophilic substitution reactions of 4,4'-biphenol and substituted hydroquinone with different difluoromonomers, The relationship between structure and properties of the novel copolymers was investigated. For the copolymers with liquid crystalline properties, their melting transition temperatures show no great change with increase the content of the crystal-disrupting unit. The reason is that the crystal phase is directly transformed from the ordered liquid crystal phase. Side-groups have important effect on mesophase stability, The temperature range of mesophase stability for the chloro-polymers is smaller than those of other series of copolymers (P-phenyl, t-butyl, methoxy, 3-trifluoromethylbenzene). This behavior indicates that the effect of geometric repulsive factor on the thermodynamic stability of the mesophase is much larger than that of the polarizability attractive factor. Different ordered liquid crystal phases are observed in the polymers with different molecular weights. At low molecular weight, highly ordered smectic liquid crystal phases form. With increasing the molecular weight, the ordered degree of the liquid crystals decreases, and only the nematic liquid crystal phase is observed in the polymer with higher molecular weight.

液晶聚芳醚酮的结构与性能研究

以联苯二酚、取代对苯二酚及含氟酮单体为原料 ,通过亲核取代反应 ,合成了系列具有液晶性的新型聚芳醚酮 .研究了聚合物分子结构与性能之间的关系 .由于结晶相是从有序的液晶相转化形成的 ,故侧基含量的增加对液晶聚合物的融熔转变温度无显著影响 .聚合物的液晶稳定性受侧基影响较大 ,含极性侧基的氯取代聚合物的液晶温区比含大空阻侧基的聚合物的液晶温区小得多 ,说明空间几何因素比极性因素对液晶稳定性的影响大 .不同分子量聚合物有不同的液晶有序结构 ,低分子量聚合物具有高有序液晶结构 ,而高分子量聚合物只有低有序的向列相结构 .

LB multilayers and superlattice films of erbium fatty acid salts

Multilayers of Y-type bilayers of pure and mixed erbium palmitate(EP), nonadecanate(Er) and behenate(EB) on CaF2 substrates were prepared by conventional Langmuir-Blodgett (LB) method. II is demonstrated that two systems composed of alternating bilayer of different fatty acid salts are unidimensional superlattices. These LB films were characterized by means of x-ray photoelectronic Spectrometry (XPS), FTIR and x-ray diffraction (XRD) measurements.

Superlattice structure of gold nanoparticles film deposited by Langmuir-Blodgett technique

Dodecanethiol-capped gold nanoparticles could spread on water subphase and be transferred by LB technique. The superlattice structure of gold nanoparticles multilayer was discussed.

Langmuir-Blodgett film formation from surfactant-capped zinc sulfide nanoparticles spread on water surface

The surfactant-capped ZnS nanoparticulate multilayer film has been fabricated by Langmuir-Blodgett(LB) technique. ZnS LB firm was investigated by the small-angle x-ray diffraction(XRD), atomic force microscopy(AFM) and transmission electron microscopy(TEM). The results indicate that ZnS nanoparticulate LB film is one-dimensional superlattice.

Preparation of SnO2 thin films with extremely preferred orientation along (101) plane by LB deposition technique

SnO2 thin films with extremely preferred orientation along (101) plane were made by LB technique and characterized by FTIR,, UV-visible, X-ray diffraction, X-ray photoelectron spectroscopy and SEM.

Preparation and characterization of DBSA doped polyaniline thin films

Stable monolayer of the polyaniline(PAn) doped with dodecyl benzenesulfonic acid(DBSA) can form on the pure water surface. The multilayer ultrathin film can be successfully deposited by Langmuir-Blodgett(LB) technique onto CaF2 substrate. The limiting mean molecular area and collapse pressure observed are 0.066 nm(2) and 35 mN m(-1), respectively. The multilayer LB film and casting film were all characterized by TR and UV-Vis-NIR spectroscopies.

Technique for determination of gold electrode area and its application of characterization in self-assembling process

Underpotential deposition(UPD) of copper at polycrystal gold surface under different concentrations has been studied, and its reversibility and stability in high concentration (0.2M CuSO4+0.IM H2SO4) have been demonstrated by cyclic voltermmetry and EQCM. A Valid approach to determine the gold electrode area in presence of adsorbed species has been provided by using Cu UPD method. Further, the growth kinetics of decane thiol on gold has also been investigated based on such a Cu UPD technique.

A rule to design high spin molecules with hetero-spin centers

The series of biradicals with m-phenylene coupling unit and hetero-spin centers were calculated compared with those possessing home-spin centers using AM1-CI method. A simple rule was proposed to design high spin molecules with ferromagnetic coupling unit and hetero-spin centers. Two neutral (or charged) hetero-spin centers resulted in high spin ground state, one neutral and another charged hetero-spin centers correspond to low spin ground state. The latter was ascribed to the huge splitting of two partially occupied molecular orbitals.