Plastic deformation of poly(tetramethylene oxide). II. Molecular orientation as measured by x-ray diffraction and NMR measurements

The orientation of the crystalline and amorphous phases in uniaxially drawn samples of polytetramethylene oxide has been studied by x-ray and NMR methods. Pole figure measurements give the orientation of the crystalline phase. Its dependence on the draw ratio does not obey the pseudoaffine model. The crystalline fraction is derived from NMR measurements at temperatures between T_g and T_m, where the free induction decay (FID) of the unoriented sample can be analyzed in terms of a rigid (crystalline), a constrained, and an amorphous phase. Low temperature (T < T_g) measurements of the NMR second-moment anisotropy in protonated and deuterated samples give a mean orientation of the chains higher than that corresponding to the crystalline phase. The lack of anisotropy in the tail of the FID at temperatures between T_g and T_m indicates no appreciable anisotropy in the truly amorphous interlamellar phase. From this and from the ratio of the P₄/P₂ orientations, factors which obey the “most probable distribution,” it is concluded that the amorphous orientation is due to the layer of constrained chains at the surface of the lamellae.     

光散射方法表征聚对苯二甲酰对苯二胺薄膜的结构特征

采用光散射方法研究了聚对苯二甲酰对苯二胺(PPTA)浓硫酸溶液于不同凝固条件下成膜时得到的球晶和草席晶等结构。PPTA的球晶由一些各向异性棒状微晶呈辐射型有序排列聚集而成的。红外二向色性的研究证明,PPTA草席晶中分子链沿“草席方向”高度取向。基于光栅衍射效应的角度依赖性认为,草席结构中条带的亮暗主要是由于它们取向方向上稍有差异引起的。以光栅效应计算了PPTA草席晶结构的长周期数据值及条带的取向状况,得到了较好的结果。根据在切应力作用下液晶的光散射图象认为,草席状结构是在切应力作用下于各向异性液业已形成,快速凝聚的方法可以把该种结构的特征保留在所获得的薄膜之中。     

FTIR and X-ray study of polymorphs of nylon 11 and relation to ferroelectricity

Nylon-11 polymorphs have been studied by x-ray diffraction and by infrared spectroscopy. A γ or γ-like phase of Nylon-11 was produced by treating the metastable δ' phase with gaseous HCl or DCl and then exposing the resulting complex (amidonium salt) to 100% RH H₂O or D₂O vapor. An oriented form of the γ or γ-like phase results from treatment of the oriented δ' phase, but stretching of the unoriented γ or γ-like phase, obtained by treatment of the unoriented δ' phase, induces a transformation to the α phase stable at room temperature. The use of DCl and D₂O produced highly deuterated samples with Fermi resonances indicating the relative strengths of the hydrogen bonds are weakest in the α phase, intermediate in the δ' phase and strongest in the γ or γ-like phase. © 1994 John Wiley & Sons, Inc.     

Structure of iodide ion arrays in iodinated nylon 6 and the chain orientation induced by iodine in nylon 6 films

Two species of iodide ions (I₃^? and I₅^?) are found in iodine—nylon 6 complexes. Orientation of I₅^? arrays (most likely I₂/I₃^? complex) along the polymer chain and I₃^? ions perpendicular to the chain axis in uniaxially drawn films and in films with planar orientation suggests that there is and intrinsic relation between the direction of iodide ion arrays and nylon 6 chains. When an unoriented film of nylon 6 in the amorphous or the α crystalline form is treated with an aqueous solution of iodine—potassium iodide, the I₃^? species in the resulting iodine—nylon complex lie in planes parallel to the surface of the film, and I₂/I₃^? units are oriented normal to the surface of the film. The γ form obtained by desorbing the iodine from this complex shows considerable uniaxial rientation with the nylon chains oriented perpendicular to the plane of the film; this orientation is maintained during the γ to α transition. It is proposed that the iodine-induced orientation of the nylon 6 chains is due to the nucleating effects of the iodide ion species as the iodine diffuses unidirectionally into the film.     

Morphology of a phase-separated and a molecular composite PBT/ABPBI polymer blend

The structure and morphology of homopolymers and blends of rigid-rod poly(p-phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide-angle x-ray diffraction and scanning and transmission electron microscopy. When samples were processed from a solution where the total polymer concentration of 30% PBT/70% ABPBI blend was greater than a critical concentration, large-scale phase separation occurred and 0.1–4 μm ellipsoidal particles were present in a ductile matrix. The ellipsoids were chiefly composed of aggregates of well-oriented 10-nm PBT crystallites, while the matrix material was chiefly ABPBI. When the concentration was less than a critical concentration, the solution was optically homogeneous. In processing of fiber and film samples from the homogeneous solution, large-scale phase separation was inhibited by rapid coagulation in a water bath. After heat treatment, these samples were found to contain crystallites of both PBT and ABPBI with lateral dimensions of ordered regions no larger than 3 nm. The PBT homopolymer was dispersed in the matrix at the molecular level in ordered regions at a scale no larger than 3 nm, resulting in a rigid-rod molecular composite. In the rigid-rod molecular composite fiber both the molecular-level dispersion and high orientation contributed to higher values of strength and modulus compared to the properties of a phase-separated fiber. The strength and modulus of highly oriented fiber were only 25% higher than those of planar isotropically oriented film, suggesting that the level of dispersion of rod molecules is more important than orientation of the reinforcing phase in rigid-rod molecular composites.     

Chitosan/N-methylol nylon 6 blend membranes for the pervaporation separation of ethanol–water mixtures

Blend membranes of chitosan and N-methylol nylon 6 were prepared by solution blending. Their pervaporation performances for the separation of ethanol–water mixtures were investigated in terms of acid (H₂SO₄) post-treatment, feed concentration, blend ratio and temperature. The pervaporation performance of the blend membranes was significantly improved by ionizing with H₂SO₄. The blend ratio of chitosan and N-methylol nylon 6 plays a different role at feed solutions of low and high water content. At a feed solution having low water content, an increase in chitosan content caused a decrease in permeability and an increase in separation factor. At a feed solution having high water content, the permeability increases with an increase in chitosan content, while the separation factor shows a maximum value around 60 wt% chitosan. It is proposed that extra permeation channels generated from the phase separation boundary between ionized chitosan and N-methylol nylon 6 account for the abnormal temperature dependence of pervaporation performance of the blend membranes.     

Piezoelectricity in uniaxially stretched and plasticized nylon 11 films

The combined effect of uniaxial stretching and plasticization of nylon 11 films on the resulting piezoelectric response was studied. Three different kinds of samples were studied for nylon 11 α′-form films: (1) uniaxially stretched at 150°C, (2) samples uniaxially stretched at 150°C and then plasticized by immersion in 2-ethyl 1,3-hexanediol, and (3) samples plasticized and then uniaxially stretched. The largest piezoelectric response was obtained from the samples which were plasticized prior to uniaxial stretching under identical poling conditions. For the case of nylon 11 δ′-form films, two different kinds of experiments were performed: (1) samples uniaxially stretched at room temperature were subsequently plasticized by immersion in the plasticizer and a comparison of their piezoelectric response made with that of the unplasticized samples as a function of poling field; (2) the plasticizer content dependence of the piezoelectric response from these samples was studied. In both cases, d₃₁ was observed to be higher for the plasticized films compared with the unplasticized films. The piezoelectric stress constant e₃₁ showed a small decrease with plasticization. X-ray diffraction studies indicated a small conversion of δ′-phase to α′-phase with plasticization. No significant changes were observed in the x-ray diffraction scans taken before and after poling.     

Porosity development in chars from thermal decomposition of poly(p-phenylene terephthalamide)

The main objective of this work was to investigate the development of porosity in solid residues from the thermal decomposition of the polymer, poly(p-phenylene terephthalamide) (PPTA). PPTA chars were prepared at different temperatures and characterized by X-ray diffraction and physical adsorption of CO₂ at 0 °C. The carbonization temperatures were selected on the basis of thermogravimetric analysis results. The effect of introducing an isothermal treatment at 500 °C on the characteristics of the resulting chars was also studied. It was found that this pre-treatment lowers the decomposition temperature of PPTA and yields a somewhat less ordered material than in the case of pyrolysis under a constant heating rate. The micropore volume increases with increasing heat treatment temperature for both series of samples. The mean micropore size decreases for the two series of chars until the 700-800 °C interval; above these temperatures, this evolution is reversed. The micropore volume of the samples submitted to the isothermal treatment is higher than when PPTA is treated under a constant heating rate. Likewise, the pore size distribution is more heterogeneous when the intermediate isothermal treatment at 500 °C is introduced during PPTA pyrolysis. Some differences between porosity development in chars from PPTA and other high thermal stability polymers were explained on the basis of different mechanistic features in polymer pyrolysis.     

Facilitated Transport of Penicillin G by Bulk Liquid Membrane with TBP as Carrier

The facilitated transport of penicillin G from aqueous solutions to the stripping phase through bulk liquid membrane (BLM) containing TBP in 3% iso-octanol and n-butyl acetate was studied. Na₂CO₃ solution was used as the stripping phase. Experiments were performed as a function of stirring rate, TBP concentration and type of diluent in the liquid membrane phase, pH, and initial penicillin G concentration in the feed phase, Na₂CO₃ concentration in the stripping phase, etc. The results showed that the BLM process could carry out the simultaneous separation and concentration of penicillin G from dilute aqueous solutions, and arise “up-hill” effect due to the characteristic of non-equilibrium mass transfer. The diffusion of penicillin G complex in the liquid membrane phase played an important role in BLM process. The mass transfer mechanism of BLM for this system was also discussed.     

聚对苯二甲酰对苯二胺/尼龙6复合物

随着材料科学的发展，纤维增强塑料已由纤维与树脂的复合，扩展到以刚性链高分子与柔性链高聚物在分子水平上的微观复合．棒状、刚性的液晶高分子是一种超高强度和超高模量的高分子材料，同时还具有在某种条件下易于自发取向形成微纤的特性．基于这些性能，液晶高分子自然成为代替无机纤维作增强剂，与柔性链高聚物进行微观复合最理想的材料．在与柔性链高聚物复合时，如何使之在基体中形成有很高的长径比（Ｌ／Ｄ）的液晶纤维，并在基体中又能起到强的增强效果，来获得高强度、高模量的复合材料．多年来一直是国际上研究的热点，有关这方面…     

THE POLYCONDENSATION OF TEREPHTHALOYL CHLORIDE AND p-PHENYLENEDIAMINE HYDROCHLORIDE IN NMP-CaCl_2 SOLVENT SYSTEM

The solution polycondensation of 1,4-phenylenediamine hydrochloride and terephthaloyl chlo-ride with introducing a tertiary amine in NMP-CaCl_2 solvent system were studied in detail.Effect of reactant concentration, the content of CaCl_2, in NMP solvent and the kinds of tertiary amineon inherent viscosity of PPTA polymer have been studied. High molecular weight PPTA withinherent viscosity over 5 was obtained at 0.35Mol/L of reactant concentration in a solvent of NMP-CaCl_2 with the presence of α-picoline.     

Polyethylene fiber formation in tubular flow. I. Observations of growth pattern and fiber properties

The process of seeded growth of fibrillar polyethylene crystals has been studied in a tubular flow geometry for 0.01-wt % solutions of a high-molecular-weight polyethylene in xylene. The transformation sequence has been followed visually by using polarized-light illumination in conjunction with a video camera. Data are presented to show that transformation is initiated by the formation of a concentrated, unoriented, amorphous precursor fiber within which oriented birefringent crystals subsequently grow in consequence of the stresses transmitted by the flowing solution. Time constants for the precursor formation, birefringence initiation, and completion of birefringence were measured as functions of temperature and flow rate over a range of growth conditions. Wide-angle x-ray diffraction, overall birefringence, and optical hot-stage melting data were also obtained on the grown fibers. The net result of these observations is to conclude that fibrillar crystal growth during flow is always preceded by the formation of a liquidlike phase transformation which produces the concentrated, unoriented precursor. Subsequent orientation is in consequence of stress-induced crystallization with overall fiber orientation showing an increase with solution flow rate at a fixed temperature and a decrease with temperature at a fixed flow rate. At higher temperatures and lower flow rates, birefringence develops in an oscillatory fashion, indicating a remelting process possibly due to slippage of trapped chain entanglements formed by flow. A discussion is given of the implications of these observations for the understanding of flow-induced structure development, phase transformation, and oriented crystallization; this is expanded upon in a companion paper, Part II.     

过剩热焓松弛CO_2和甲苯在PET薄膜中渗透的影响

本文研究了非晶态、未取向PET薄膜样品在低于T_g温度以下热处理,结构的变化和过剩热焓松弛对CO_2和甲苯溶剂在样品中渗透速率的影响。结果表明,随退火时间增加,从T_g转变吸热峰确定的过剩热焓松弛量、 T_g温度、密度增加,而反式构象含量减少。除分子链堆砌密度提高或自由体积下降外,没有发现非晶相有结构上的变化。因此,CO_2在样品中随退火时间的增加渗透速率下降。然而,由于样品脆性增加和甲苯的溶胀作用,样品表面出现裂纹,使甲苯在样品中的表观渗透速率增加。     

Behavior of thermosensitive graft copolymer with aromatic polyester backbone and poly-2-ethyl-2-oxazoline side chains in aqueous solutions

Thermoresponsive graft copolymers with alkylene-aromatic polyester main chain and poly-2-ethyl-2-oxazoline side chains were synthesized. Two copolymer samples which differed in grafting density (0.5 and 0.7) were studied using dynamic and static light scattering and turbidimetry in aqueous solutions at concentration 0.0053?g?cm^?3. Hydrodynamic radii of scattering objects and their contribution to light scattering were obtained as a function of temperature in a wide temperature interval. Temperatures of phase separation were found out. Effect of grafting density on the copolymer behavior in aqueous solutions upon heating was determined. In particular, the phase separation temperature reduces with the decreasing grafting density.     

自生长燃烧法合成纳米铁酸钇固溶体光催化剂

以硝酸铁和硝酸钇作为前驱体,甘氨酸为燃料用自生长燃烧法合成了可见光光催化剂YFeO₃及其固溶体。样品通过X射线粉末衍射(XRD)、N₂吸附、紫外-可见漫反射(UV-Vis DRS)、扫描电子显微镜(SEM)和透射电镜(TEM)等表征了其晶相结构、BET比表面积和形貌。结果表明掺杂一定量的金属能有效地提高自生长燃烧法合成的YFeO₃的纯度,所合成的样品晶粒大小约为55 nm。与YFeO₃相比其固溶体吸收边红移。光催化降解亚甲基蓝(MB)和罗丹明B(RhB)结果表明YFeO₃及其固溶体均具有活性,Bi修饰的YFeO₃表现出最高的光催化活性,而且对于不同染料的降解程度不同。     

Solid Solutions of WO3into Zirconia in WO3-ZrO2 Catalysts

Catalysts in the WO₃-ZrO₂ system were produced by coprecipitation of aqueous solutions of zirconium oxynitrate and ammonium metatungstate. Samples were characterized by X-ray powder diffraction, thermogravimetry, and refinement of their crystalline structures with the Rietveld method. This coprecipitation gave rise to solid solutions of tungsten oxide into zirconia; the initial phase was amorphous and crystallized into two tetragonal crystalline phases, T1 and T2, when samples were annealed at 560°C. The main difference between both phases was the oxygen position along the c axis. In the phase with higher symmetry, T2, an oxygen atom was at one-half of the unit cell, 0.50(2), producing flat crystallite surfaces perpendicular to the c axis, while in the phase with the lower symmetry, T1, it was at 0.447(2), and gave rise to rough crystallite surfaces parallel to (100) planes. The interpenetrating tetrahedra forming the representative polyhedron of the crystalline structure were almost nondeformed in the phase with higher symmetry, because all Zr-O atom bond lengths were very similar. As the annealing temperature of the sample was increased, the dissolved tungsten atoms in the phase with higher symmetry segregated to the crystallite's surface.     

Extraction of Lanthanide Nitrates in Multicomponent Aqueous-Organic Two-Phase Systems with D2EHPA

Lanthanum nitrate distribution in three-component aqueous-organic systems with D2EHPA from acetate or acetic acid–acetate solutions has been studied, it has been shown that variation in sodium acetate concentration or composition of CH₃COONa–CH₃COOH mixture can affect metal distribution ratios. It has been found that extraction in three-component mixture of 1: 1: 1 composition (aqueous solution Ln(NO₃)₃ + CH₃COONa + CH₃COOH–D2EHPA in hexane–isopropyl alcohol) can provide lanthanide separation, which is dependent on the ratio of sodium acetate and acetic acid in aqueous phase and on D2EHPA concentration in organic phase. Lanthanide–lanthanum separation factors have been calculated for the extraction of lanthanide nitrates from acetic acid–acetate solutions.     

Influence of silver doping on the electrical and magnetic behavior of La0.7Ca0.3MnO3 manganites

A systematic investigation of structural, magnetic and magnetotransport behavior of La_0.7Ca_0.3?xAg_xMnO₃ manganites has been undertaken. The X-ray diffraction shows a structural transformation from orthorhombic to rhombohedral with increasing Ag concentration. The undoped and 10% Ag substituted samples exhibit double transition in M–T curves. The electrical resistivity in the entire temperature range is fitted to effective medium approximation and phase separation models. The sign of S changes from negative to positive with increase in Ag doping. The low temperature thermopower data has been fitted to an equation containing diffusion, magnon drag and phonon drag terms. The paramagnetic insulting part of the TEP data has been analyzed using small polaron hopping mechanism.     

Phase equilibria and some properties of solid solutions in the Tl5Te3-Tl9BiTe6-Tl5Te2Cl system

Phase equilibria in the Tl₅Te₃-Tl₉BiTe6-Tl₅Te₂Cl system were studied by differential thermal analysis (DTA), X-ray powder diffraction, and measurements of microhardness and also emf of concentration circuits with reference to a thallium electrode. A number of polythermal sections, the isothermal sections of the phase diagram at 760 and 800 K, and projections of the liquidus and solidus surfaces were constructed. It was shown that the system is characterized by the formation of unlimited solid solutions with the Tl₅Te₃ structure. The concentration dependences of the crystal lattice parameters, microhardness, and emf in the solid solutions were described.     

Viscoelasticity of oriented poly(ethylene terephthalate)

Time–temperature superposition can be successfully applied to both the stress relaxation and dynamic mechanical properties of oriented PET fibers. Two curves result; one is the time dependence of the modulus at constant temperature, while the other is the shift, log aT, of this curve along the time scale as a function of temperature. This temperature dependence is less than that for both unoriented PET and typical amorphous polymers above T_g. It is about the same as that for oriented nylon 66 and unoriented glassy poly(methyl methacrylate). The isothermal modulus has the same time dependence as that of the unoriented PET; however, it is a factor of 3.3 larger. The modulus curve is almost identical in both shape and magnitude with that of oriented nylon 66. However, a temperature of 82°C. is required to place the viscoelastic dispersion region of PET at the same time scale as nylon 66 at 25°C. This temperature increase is the major difference in viscoelasticity between these two oriented polymers.